| 1. |
- Boeddinghaus, Runa S., et al.
(författare)
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The mineralosphere—interactive zone of microbial colonization and carbon use in grassland soils
- 2021
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Ingår i: Biology and Fertility of Soils. - : Springer Science and Business Media LLC. - 0178-2762 .- 1432-0789. ; 57:5, s. 587-601
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Tidskriftsartikel (refereegranskat)abstract
- To improve our understanding of early microbial colonization of pristine minerals and their group-specific C utilization, we exposed minerals (illite/goethite/quartz) amended with artificial root exudates (ARE, glucose, and citric acid) in grassland soils for a period of 24 weeks. FTIR spectra indicated that mineral-associated ARE were used within the first 2 weeks of exposure and were replaced by other carbohydrates derived from living or dead cells as well as soil-borne C sources transported into the mineralosphere after heavy rain events. Fungi and Gram-positive bacteria incorporated ARE-derived C more rapidly than Gram-negative bacteria. Gram-negative bacteria presumably profited indirectly from the ARE by cross-feeding on mineral-associated necromass of fungi and Gram-positive bacteria. The Gram-negative bacterial phyla Verrucomicrobia, Planctomycetes, Gemmatimonadetes, Armatimonadetes, and Chloroflexi showed a positive correlation with Gram-negative PLFA abundances. After 24 weeks of exposure in the grassland soils, abundances of soil microorganisms in the mineralosphere reached only 3.1% of the population density in soil. In conclusion, both bacteria and fungi slowly colonize new surfaces such as pristine minerals, but quickly assimilate artificial root exudates, creating an active microbial community in the mineralosphere.
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| 2. |
- Hicks, Lettice C., et al.
(författare)
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Simulated rhizosphere deposits induce microbial N-mining that may accelerate shrubification in the subarctic
- 2020
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 101:9
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Tidskriftsartikel (refereegranskat)abstract
- Climate change is exposing high-latitude systems to warming and a shift towards more shrub-dominated plant communities, resulting in increased leaf-litter inputs at the soil surface, and more labile root-derived organic matter (OM) input in the soil profile. Labile OM can stimulate the mineralization of soil organic matter (SOM); a phenomenon termed “priming.” In N-poor subarctic soils, it is hypothesized that microorganisms may “prime” SOM in order to acquire N (microbial N-mining). Increased leaf-litter inputs with a high C/N ratio might further exacerbate microbial N demand, and increase the susceptibility of N-poor soils to N-mining. We investigated the N-control of SOM mineralization by amending soils from climate change–simulation treatments in the subarctic (+1.1°C warming, birch litter addition, willow litter addition, and fungal sporocarp addition) with labile OM either in the form of glucose (labile C; equivalent to 400 µg C/g fresh [fwt] soil) or alanine (labile C + N; equivalent to 400 µg C and 157 µg N/g fwt soil), to simulate rhizosphere inputs. Surprisingly, we found that despite 5 yr of simulated climate change treatments, there were no significant effects of the field-treatments on microbial process rates, community structure or responses to labile OM. Glucose primed the mineralization of both C and N from SOM, but gross mineralization of N was stimulated more than that of C, suggesting that microbial SOM use increased in magnitude and shifted to components richer in N (i.e., selective microbial N-mining). The addition of alanine also resulted in priming of both C and N mineralization, but the N mineralization stimulated by alanine was greater than that stimulated by glucose, indicating strong N-mining even when a source of labile OM including N was supplied. Microbial carbon use efficiency was reduced in response to both labile OM inputs. Overall, these findings suggest that shrub expansion could fundamentally alter biogeochemical cycling in the subarctic, yielding more N available for plant uptake in these N-limited soils, thus driving positive plant–soil feedbacks.
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| 3. |
- Hicks, Lettice C., et al.
(författare)
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Soil Microbial Responses to 28 Years of Nutrient Fertilization in a Subarctic Heath
- 2020
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 23:5, s. 1107-1119
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Tidskriftsartikel (refereegranskat)abstract
- Arctic and subarctic soils are typically characterized by low nitrogen (N) availability, suggesting N-limitation of plants and soil microorganisms. Climate warming will stimulate the decomposition of organic matter, resulting in an increase in soil nutrient availability. However, it remains unclear how soil microorganisms in N-limited soils will respond, as the direct effect of inorganic N addition is often shown to inhibit microbial activity, while elevated N availability may have a positive effect on microorganisms indirectly, due to a stimulation of plant productivity. Here we used soils from a long-term fertilization experiment in the Subarctic (28 years at the time of sampling) to investigate the net effects of chronic N-fertilization (100 kg N ha−1 y−1, added together with 26 kg P and 90 kg K ha−1 y−1, as expected secondary limiting nutrients for plants) on microbial growth, soil C and N mineralization, microbial biomass, and community structure. Despite high levels of long-term fertilization, which significantly increased primary production, we observed relatively minor effects on soil microbial activity. Bacterial growth exhibited the most pronounced response to long-term fertilization, with higher rates of growth in fertilized soils, whereas fungal growth remained unaffected. Rates of basal soil C and N mineralization were only marginally higher in fertilized soils, whereas fertilization had no significant effect on microbial biomass or microbial community structure. Overall, these findings suggest that microbial responses to long-term fertilization in these subarctic tundra soils were driven by an increased flow of labile plant-derived C due to stimulated plant productivity, rather than by direct fertilization effects on the microbial community or changes in soil physiochemistry.
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| 4. |
- Hicks, Lettice
(författare)
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Increased Above- and Belowground Plant Input Can Both Trigger Microbial Nitrogen Mining in Subarctic Tundra Soils
- 2022
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 25:1, s. 105-121
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Tidskriftsartikel (refereegranskat)abstract
- Low nitrogen (N) availability in the Arctic and Subarctic constrains plant productivity, resulting in low litter inputs to soil. Increased N availability and litter inputs as a result of climate change, therefore, have the potential to impact the functioning of these ecosystems. We examined plant and microbial responses to chronic inorganic N (5 g m−2 year−1) and/or litter (90 g m−2 year−1), supplied during three growing seasons. We also compared the response to more extreme additions, where the total cumulative additions of N (that is, 15 g m−2) and litter (that is, 270 g m−2) were concentrated into a single growth season. Plant productivity was stimulated by N additions and was higher in the extreme addition plots than those with chronic annual additions. Microbial community structure also differed between the chronic and extreme plots, and there was a significant relationship between plant and microbial community structures. Despite differences in microbial structure, the field treatments had no effect on microbial growth or soil C mineralization. However, gross N mineralization was higher in the N addition plots. This led to a lower ratio of soil C mineralization to gross N mineralization, indicating microbial targeting of N-rich organic matter (“microbial N-mining”), likely driven by the increased belowground C-inputs due to stimulated plant productivity. Surprisingly, aboveground litter addition also decreased ratio of soil C mineralization to gross N mineralization. Together, these results suggest that elevated N availability will induce strong responses in tundra ecosystems by promoting plant productivity, driving changes in above- and belowground community structures, and accelerating gross N mineralization. In contrast, increased litter inputs will have subtle effects, primarily altering the ratio between C and N derived from soil organic matter.
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| 5. |
- Rousk, Johannes, et al.
(författare)
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Responses of microbial tolerance to heavy metals along a century-old metal ore pollution gradient in a subarctic birch forest
- 2018
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Ingår i: Environmental Pollution. - : Elsevier BV. - 0269-7491. ; 240, s. 297-305
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Tidskriftsartikel (refereegranskat)abstract
- Heavy metals are some of the most persistent and potent anthropogenic environmental contaminants. Although heavy metals may compromise microbial communities and soil fertility, it is challenging to causally link microbial responses to heavy metals due to various confounding factors, including correlated soil physicochemistry or nutrient availability. A solution is to investigate whether tolerance to the pollutant has been induced, called Pollution Induced Community Tolerance (PICT). In this study, we investigated soil microbial responses to a century-old gradient of metal ore pollution in an otherwise pristine subarctic birch forest generated by a railway source of iron ore transportation. To do this, we determined microbial biomass, growth, and respiration rates, and bacterial tolerance to Zn and Cu in replicated distance transects (1 m–4 km) perpendicular to the railway. Microbial biomass, growth and respiration rates were stable across the pollution gradient. The microbial community structure could be distinguished between sampled distances, but most of the variation was explained by soil pH differences, and it did not align with distance from the railroad pollution source. Bacterial tolerance to Zn and Cu started from background levels at 4 km distance from the pollution source, and remained at background levels for Cu throughout the gradient. Yet, bacterial tolerance to Zn increased 10-fold 100 m from the railway source. Our results show that the microbial community structure, size and performance remained unaffected by the metal ore exposure, suggesting no impact on ecosystem functioning. An induced bacterial Zn-tolerance demonstrated that pristine soil microbial communities had been contaminated by metal pollution derived from iron ore transport.
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| 6. |
- Rousk, Kathrin, et al.
(författare)
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Feather moss nitrogen acquisition across natural fertility gradients in boreal forests
- 2013
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 61, s. 86-95
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Tidskriftsartikel (refereegranskat)abstract
- Feather mosses utilize various sources of nitrogen (N): they absorb N deposited on leaf tissue, they host N-2 fixing cyanobacteria, and they are able to take up N directly from soil. In addition to their importance as primary producers in boreal ecosystems, feather mosses play a significant role in N cycling. However, estimates of their ability to take up N from soil in situ are scarce. Further, connecting uptake of N from soil with N-2 fixation could significantly improve our understanding of their role in ecosystem N cycling, but to date this issue has not been addressed. We report results from an uptake experiment in which we tracked C-13-carbon (C), N-15-alanine and N-15-ammonium chloride (NH4Cl) into feather moss (Pleurozium schreberi (Brid.) Mitt.)-soil cores taken along natural fertility gradients in Northern Sweden. The varying fertility conditions coincided with a N-2 fixation gradient in the feather moss. We found that P. schreberi takes up C and N directly from soil. However, the moss did not show a preference for inorganic or organic N sources and only 1.4% of the added amino acid appeared to be taken up from soil in an intact form. No differences in uptake of C or N from soil along the fertility gradients were detected. Nitrogen fixation rates in the moss were thus not correlated with C or N-uptake from soil. Nitrogen fixation as well as uptake of C and N from soil seem to be unaffected by C or N availability in the soil, suggesting that the moss can cover its nutrient demand by absorption of throughfall N and via associated N-2-fixing cyanobacteria without soil-N supplementation. We suggest further, that the moss can represent a (temporary) N-sink in the boreal forest, and that the moss' mechanism of uptake and release thereby will characterize the ecosystem N cycle. (C) 2013 Elsevier Ltd. All rights reserved.
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| 7. |
- Rousk, Kathrin, et al.
(författare)
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Microbial control of soil organic matter mineralization responses to labile carbon in subarctic climate change treatments
- 2016
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 22:12, s. 4150-4161
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Tidskriftsartikel (refereegranskat)abstract
- Half the global soil carbon (C) is held in high-latitude systems. Climate change will expose these to warming and a shift towards plant communities with more labile C input. Labile C can also increase the rate of loss of native soil organic matter (SOM); a phenomenon termed ‘priming’. We investigated how warming (+1.1 °C over ambient using open top chambers) and litter addition (90 g m−2 yr−1) treatments in the subarctic influenced the susceptibility of SOM mineralization to priming, and its microbial underpinnings. Labile C appeared to inhibit the mineralization of C from SOM by up to 60% within hours. In contrast, the mineralization of N from SOM was stimulated by up to 300%. These responses occurred rapidly and were unrelated to microbial successional dynamics, suggesting catabolic responses. Considered separately, the labile C inhibited C mineralization is compatible with previously reported findings termed ‘preferential substrate utilization’ or ‘negative apparent priming’, while the stimulated N mineralization responses echo recent reports of ‘real priming’ of SOM mineralization. However, C and N mineralization responses derived from the same SOM source must be interpreted together: This suggested that the microbial SOM-use decreased in magnitude and shifted to components richer in N. This finding highlights that only considering SOM in terms of C may be simplistic, and will not capture all changes in SOM decomposition. The selective mining for N increased in climate change treatments with higher fungal dominance. In conclusion, labile C appeared to trigger catabolic responses of the resident microbial community that shifted the SOM mining to N-rich components; an effect that increased with higher fungal dominance. Extrapolating from these findings, the predicted shrub expansion in the subarctic could result in an altered microbial use of SOM, selectively mining it for N-rich components, and leading to a reduced total SOM-use.
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| 8. |
- Rousk, Kathrin, et al.
(författare)
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The Cyanobacterial Role in the Resistance of Feather Mosses to Decomposition-Toward a New Hypothesis
- 2013
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Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:4
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Tidskriftsartikel (refereegranskat)abstract
- Cyanobacteria-plant symbioses play an important role in many ecosystems due to the fixation of atmospheric nitrogen (N) by the cyanobacterial symbiont. The ubiquitous feather moss Pleurozium schreberi (Brid.) Mitt. is colonized by cyanobacteria in boreal systems with low N deposition. Here, cyanobacteria fix substantial amounts of N-2 and represent a potential N source. The feather moss appears to be resistant to decomposition, which could be partly a result of toxins produced by cyanobacteria. To assess how cyanobacteria modulated the toxicity of moss, we measured inhibition of bacterial growth. Moss with varying numbers of cyanobacteria was added to soil bacteria to test the inhibition of their growth using the thymidine incorporation technique. Moss could universally inhibit bacterial growth, but moss toxicity did not increase with N-2 fixation rates (numbers of cyanobacteria). Instead, we see evidence for a negative relationship between moss toxicity to bacteria and N-2 fixation, which could be related to the ecological mechanisms that govern the cyanobacteria - moss relationship. We conclude that cyanobacteria associated with moss do not contribute to the resistance to decomposition of moss, and from our results emerges the question as to what type of relationship the moss and cyanobacteria share.
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| 9. |
- Rousk, Kathrin, et al.
(författare)
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The responses of moss-associated nitrogen fixation and belowground microbial community to chronic Mo and P supplements in subarctic dry heaths
- 2020
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Ingår i: Plant and Soil. - : Springer Science and Business Media LLC. - 0032-079X .- 1573-5036. ; 451:1-2, s. 261-276
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Although nitrogen (N) fixation by moss-associated bacteria is the main source of new N in N-limited ecosystems like arctic tundra, we do not know which nutrient, molybdenum (Mo) or phosphorus (P), is rate-limiting for sustaining this process in the long-term. Further, how moss-associated N2 fixation impacts the belowground microbial regulation of decomposition remains unresolved. Methods: Moss-associated N2 fixation and soil microbial process rates, abundance and community structure were assessed in long-term P and Mo field additions in the Subarctic during three years. Results: We found tendencies for stimulation of moss-associated N2 fixation by Mo in the short term, by P in the long-term, and tendencies for a stimulation of soil microbial activity by P. However, large variation in microbial activity within and below the moss exceeded any systematic variation induced by the field treatments. Our findings suggest that soil microbial activity is not limited by N at our site, and that Mo and P only occasionally limit N2 fixation during a growing season. Conclusions: Since increasing CO2 concentrations can induce nutrient limitation, the here reported transient limitation can easily shift into a chronic one with significant implications for ecosystem productivity and biogeochemistry.
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| 10. |
- Ackermann, Kathrin, et al.
(författare)
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N-2 Fixation in Feather Mosses is a Sensitive Indicator of N Deposition in Boreal Forests
- 2012
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Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 15:6, s. 986-998
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Tidskriftsartikel (refereegranskat)abstract
- Nitrogen (N) fixation in the feather moss-cyanobacteria association represents a major N source in boreal forests which experience low levels of N deposition; however, little is known about the effects of anthropogenic N inputs on the rate of fixation of atmospheric N-2 in mosses and the succeeding effects on soil nutrient concentrations and microbial community composition. We collected soil samples and moss shoots of Pleurozium schreberi at six distances along busy and remote roads in northern Sweden to assess the influence of road-derived N inputs on N-2 fixation in moss, soil nutrient concentrations and microbial communities. Soil nutrients were similar between busy and remote roads; N-2 fixation was higher in mosses along the remote roads than along the busy roads and increased with increasing distance from busy roads up to rates of N-2 fixation similar to remote roads. Throughfall N was higher in sites adjacent to the busy roads but showed no distance effect. Soil microbial phospholipid fatty acid (PLFA) composition exhibited a weak pattern regarding road type. Concentrations of bacterial and total PLFAs decreased with increasing distance from busy roads, whereas fungal PLFAs showed no distance effect. Our results show that N-2 fixation in feather mosses is highly affected by N deposition, here derived from roads in northern Sweden. Moreover, as other measured factors showed only weak differences between the road types, atmospheric N-2 fixation in feather mosses represents a highly sensitive indicator for increased N loads to natural systems.
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| 11. |
- Alfredsson, Hanna, et al.
(författare)
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Bacterial and fungal colonization and decomposition of submerged plant litter: consequences for biogenic silica dissolution.
- 2016
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Ingår i: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941. ; 92:3
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Tidskriftsartikel (refereegranskat)abstract
- We studied bacterial and fungal colonization of submerged plant litter, using a known Si-accumulator (Equisetum arvense), in experimental microcosms during one month. We specifically addressed the microbial decomposer role concerning biogenic silica (bSiO2) dissolution from the degrading litter. To vary the rates and level of microbial colonization, the litter was combined with a range of mineral nitrogen (N) and phosphorous (P) supplements. Overall microbial growth on plant litter increased with higher levels of N and P. There was a tendency for higher bacterial than fungal stimulation with higher nutrient levels. Differences in microbial colonization of litter between treatments allowed us to test how Si remineralization from plants was influenced by microbial litter decomposition. Contrary to previous results and expectations, we observed a general reduction in Si release from plant litter colonized by a microbial community, compared with sterile control treatments. This suggested that microbial growth resulted in a reduction in dissolved Si concentrations, and we discuss candidate mechanisms to explain this outcome. Hence, our results imply that the microbial role in plant litter associated Si turnover is different from that commonly assumed based on bSiO2 dissolution studies in aquatic ecosystems.
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| 12. |
- Averill, Colin, et al.
(författare)
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Microbial-mediated redistribution of ecosystem nitrogen cycling can delay progressive nitrogen limitation
- 2015
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Ingår i: Biogeochemistry. - : Springer Science and Business Media LLC. - 1573-515X .- 0168-2563. ; 126:1-2, s. 11-23
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Tidskriftsartikel (refereegranskat)abstract
- Soil nitrogen (N) availability constrains future predictions of ecosystem primary productivity and carbon storage. The progressive N limitation (PNL) hypothesis predicts that forest net primary productivity (NPP) will decline with age, and that the response of NPP to elevated CO2 will attenuate through time due to negative feedbacks of NPP on the soil N cycle. A central assumption of the PNL hypothesis is that, without changes in exogenous exchange of N in an ecosystem, increases in plant N uptake require increased soil N cycling rates. However, at ecosystem scale, microbial N uptake exceeds plant uptake. Hence, a change in the partitioning of N between plants and soil microorganisms may represent an alternative mechanism to sustain plant N uptake in the face of PNL. To estimate N partitioning of total N cycling between plants and microbes, we measured and modeled growth and N uptake of trees, bacteria, saprotrophic fungi, and ectomycorrhizal fungi across a forest succession and N limitation gradient. The combined plant and ectomycorrhizal N uptake increased from early to late succession, and nearly matched saprotrophic N uptake in late successional sites, while total N cycling remained stable or even declined. Changes in microbial community structure can thus mediate a redistribution of ecosystem nitrogen cycling, allowing an increase in plant N uptake without concomitant increases in soil N cycling. We further suggest that microbe-mediated changes in N partitioning can delay PNL and may thereby act as a mechanism to extend the duration of the land carbon sink in response to rising atmospheric CO2.
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| 13. |
- Bapiri, Azadeh, et al.
(författare)
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Drying-Rewetting Cycles Affect Fungal and Bacterial Growth Differently in an Arable Soil
- 2010
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Ingår i: Microbial Ecology. - : Springer Science and Business Media LLC. - 1432-184X .- 0095-3628. ; 60:2, s. 419-428
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Tidskriftsartikel (refereegranskat)abstract
- Drying and rewetting is a frequent physiological stress for soil microbial communities; a stress that is predicted to grow more influential with future climate change. We investigated the effect of repeated drying-rewetting cycles on bacterial (leucine incorporation) and fungal (acetate in ergosterol incorporation) growth, on the biomass concentration and composition (PLFA), and on the soil respiration. Using different plant material amendments, we generated soils with different initial fungal:bacterial compositions that we exposed to 6-10 repetitions of a drying-rewetting cycle. Drying-rewetting decreased bacterial growth while fungal growth remained unaffected, resulting in an elevated fungal:bacterial growth ratio. This effect was found irrespective of the initial fungal:bacterial biomass ratio. Many drying-rewetting cycles did not, however, affect the fungal:bacterial growth ratio compared to few cycles. The biomass response of the microbial community differed from the growth response, with fungal and total biomass only being slightly negatively affected by the repeated drying-rewetting. The discrepancy between growth- and biomass-based assessments underscores that microbial responses to perturbations might previously have been misrepresented with biomass-based assessments. In light of this, many aspects of environmental microbial ecology may need to be revisited with attention to what measure of the microbial community is relevant to study.
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| 14. |
- Barcenas-Moreno, Gema, et al.
(författare)
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Adaptation of soil microbial communities to temperature: comparison of fungi and bacteria in a laboratory experiment
- 2009
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 15:12, s. 2950-2957
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Tidskriftsartikel (refereegranskat)abstract
- Temperature not only has direct effects on microbial activity, but can also affect activity indirectly by changing the temperature dependency of the community. This would result in communities performing better over time in response to increased temperatures. We have for the first time studied the effect of soil temperature (5-50 degrees C) on the community adaptation of both bacterial (leucine incorporation) and fungal growth (acetate-in-ergosterol incorporation). Growth at different temperatures was estimated after about a month using a short-term assay to avoid confounding the effects of temperature on substrate availability. Before the experiment started, fungal and bacterial growth was optimal around 30 degrees C. Increasing soil temperature above this resulted in an increase in the optimum for bacterial growth, correlated to soil temperature, with parallel shifts in the total response curve. Below the optimum, soil temperature had only minor effects, although lower temperatures selected for communities growing better at the lowest temperature. Fungi were affected in the same way as bacteria, with large shifts in temperature tolerance at soil temperatures above that of optimum for growth. A simplified technique, only comparing growth at two contrasting temperatures, gave similar results as using a complete temperature curve, allowing for large scale measurements also in field situations with small differences in temperature.
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| 15. |
- Bárcenas-Moreno, Gema, et al.
(författare)
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Functional implications of the pH-trait distribution of the microbial community in a re-inoculation experiment across a pH gradient
- 2016
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 93, s. 69-78
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Tidskriftsartikel (refereegranskat)abstract
- We compared the influence of the microbial community composition and the environmental conditions for the functioning - microbial growth and respiration - and trait distribution - bacterial pH tolerance - of soil microorganisms across a pH gradient. Sterilised soil microcosms, including pH 4.1, 5.2, 6.7 and 8.3, with added plant litter were inoculated with unsterilized soil in a factorial design and monitored during two months. The trait distribution - pH-tolerance - of bacterial communities converged with the pH of the soil environment. Still, the different inoculum communities could result in suboptimal pH-tolerance in all soil pH environments; inoculum communities derived from low pHs had lower than optimal pH-tolerance in high soil pH environments, and vice versa. The functioning of bacterial communities with trait distributions mismatched to the soil pH environment was impaired. The legacy of the initial bacterial trait distribution on bacterial pH tolerance and functioning was detected within one week and remained for two months in all soil pH environments. Fungal inoculum communities derived from low compared to high pHs resulted in higher fungal functioning. Thus, in contrast with bacteria there was no evidence that variation in pH-tolerance influenced fungal performance. Instead the fungal inoculum size appeared to explain these results. Bacteria dominated respiration in high pH while fungi dominated at low pH environments. Consequently, respiration was affected by how well-matched the bacterial trait distribution was to the pH of the soil environment at higher pHs. At low pH, the inoculum size of fungi appeared to determine the respiration.
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| 16. |
- Barcenas-Moreno, Gema, et al.
(författare)
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Fungal and bacterial recolonisation of acid and alkaline forest soils following artificial heat treatments
- 2011
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 43:5, s. 1023-1033
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Tidskriftsartikel (refereegranskat)abstract
- The direct response and the short-term recolonisation of soil by fungi and bacteria were studied after heat treatments of a humus soil with high carbon content and low pH. and a calcareous soil with lower carbon content and high pH. Heating was administered using a muffle furnace or an autoclave, with different temperatures and times of heat exposure, after which fresh soil (1%) was added as inoculum. Autoclaved soil showed more marked increases in bacterial growth during the recovery phase than oven-heated soil, and the bacterial growth response was more rapid in calcareous than in humus soil. Fungal growth recovered more rapid and reached values higher than the control in humus soil, while it remained low until the end of the study in calcareous soil. Respiration rate showed similar patterns in both soils. Fungal biomass (ergosterol and PLFA 18:2w6.9) indicated that fungi benefited by autoclaving in humus soil, while they were disfavoured by this treatment in calcareous soil. The sum of bacterial PLFAs did not change due to heating, but some bacterial PLFAs (e.g. cy17:0) increased in both soils. We propose that the community assembly of the microbial communities after heating were mainly driven by pH, in that the high pH soil selected primarily for bacteria and the low pH soil for fungi. (C) 2011 Elsevier Ltd. All rights reserved.
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| 17. |
- Bengtson, Per, et al.
(författare)
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Archaeal abundance across a pH gradient in an arable soil and its relationship with bacterial and fungal growth rates.
- 2012
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 78:16, s. 5906-5911
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Tidskriftsartikel (refereegranskat)abstract
- Soil pH is one of the most influential factors for the composition of bacterial and fungal communities, but the influence of soil pH on the distribution and composition of soil archaeal communities has yet to be systematically addressed. The primary aim of this study was to determine how total archaeal abundance (qPCR based estimates of 16S rRNA gene copy numbers) is related to soil pH across a pH gradient (pH 4.0-8.3). Secondarily, we wanted to assess how archaeal abundance related to bacterial and fungal growth rates across the same pH gradient. We identified two distinct and opposite effects of pH on the archaeal abundance. In the lowest pH range (pH 4.0-4.7) the abundance of archaea did not seem to respond to pH. Above this pH range there was a sharp, almost 4-fold, decrease in archaeal abundance, reaching a minimum at pH 5.1-5.2. The low archaeal abundance of archaeal 16S rRNA gene copies at this pH then sharply increased almost 150-fold with pH, resulting in an increase in the ratio between archaeal and bacterial copy numbers from a minimum of 0.002 to more than 0.07 at pH 8. The non-uniform archaeal response to pH could reflect variation in the archaeal community composition along the gradient, with some archaea adapted to acidic conditions, and others to neutral to slightly alkaline conditions. This suggestion is reinforced by observations of contrasting outcomes of the (competitive) interactions between archaea, bacteria and fungi towards the lower and higher ends of the examined pH gradient.
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| 18. |
- Benito-Carnero, Garazi, et al.
(författare)
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Low-quality carbon and lack of nutrients result in a stronger fungal than bacterial home-field advantage during the decomposition of leaf litter
- 2021
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Ingår i: Functional Ecology. - : Wiley. - 0269-8463 .- 1365-2435. ; 35:8, s. 1783-1796
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Tidskriftsartikel (refereegranskat)abstract
- Decomposition of litter is a key biochemical process that regulates the rate and magnitude of CO2 fluxes from biosphere to atmosphere and determines soil nutrient availability. Although several studies have shown that plant litter decomposition accelerated in their native compared to a foreign environment, that is, a home-field advantage (HFA) for litter degradation, to date HFA has only been considered in terms of respiration or litter mass loss. The competitive success of the decomposer micro-organism will be determined by its ability to transform used OM into population growth. Therefore, we hypothesized that HFA for microbial growth would be more pronounced than that for decomposition. We also expected that HFA effect for decomposition and microbial growth would increase with lower quality litter, which the fungal role in litter decomposition would be more dominant than that of bacteria, and that HFA effects would strengthen with more pronounced differences between ‘home’ and ‘away’ environments. We designed a 2-month microcosm reciprocal transplant experiment with litter from two sites with contrasting climates (Atlantic and Sub-Mediterranean climates) and including three tree species (Quercus robur, Pinus sylvestris and Fagus sylvatica). We found a stronger HFA for microbial growth than for decomposition, that the nutrient content and C-quality of litter influenced the microbial HFA and that interactions between bacterial and fungal communities during litter decomposition modulated the HFA for litter degradation. Low litter nutrient content, strong nutrient limitations and low C-qualities all favoured fungal over bacterial decomposers, and our results suggest a dominant functional role of the fungal community and gave rise to HFA effect for fungal growth but that this translated to only marginal implications for overall decomposition of litter. A free Plain Language Summary can be found within the Supporting Information of this article.
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| 19. |
- Birgander, Johanna, et al.
(författare)
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Activity of temperate grassland plants and symbiotic fungi during the winter - implications for community structure and carbon cycling in a changing climate
- 2012
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Ingår i: Nordic Journal of Botany. - : Wiley. - 0107-055X. ; 30:5, s. 513-521
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Tidskriftsartikel (refereegranskat)abstract
- Several investigations have revealed surprisingly high activities during the winter in vegetation and soil in temperate and subarctic areas. Plants have been found to photosynthesize even under snow cover and at temperatures below freezing, and decomposer microorganisms can function, at low rates, all year around. In temperate grasslands, the vegetation includes winter annual herbs as well as bryophytes, which have the potential to be active and are thus susceptible to changing temperatures during winter. If temperatures stay below freezing and there is a snow cover, an increase in temperatures could in fact decrease the soil temperature due to reduced insulation by snow cover. On the other hand, if winter temperatures initially fluctuate around the freezing point, an increase by a few degrees might produce frost-free conditions. Based on available data, the composition of plant communities are strongly influenced by temperature conditions in the preceding winter. We conclude that the winter season in grasslands needs more research attention, to start to resolve which species are active and how they respond to a changing climate.
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| 20. |
- Birgander, Johanna, et al.
(författare)
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Comparison of fertility and seasonal effects on grassland microbial communities
- 2014
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 76, s. 80-89
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Tidskriftsartikel (refereegranskat)abstract
- The activity of saprotrophic fungi and bacteria, and the balance between them, can affect decomposition. Arbuscular mycorrhizal (AM) fungi are also important for the nutrient and energy transfer in soil. Microbial community composition and activity are believed to have seasonal patterns, and are known to be highly influenced by environmental factors such as pH and nutrient conditions. To evaluate the importance of season for the variation in microbial decomposer community in a context of well-known environmental factor variation, we studied microbial growth, biomass and community structure along a fertility gradient (pH 5.9-8.1; NH4-N 3-19 mu g g(-1) soil, f.w.) in a sandy grassland during one year. The microbial community structure (phospholipid fatty acid (PLFA) composition) and biomass (PLFA and neutral lipid fatty acid (NLFA) signatures) as well as fungal (acetate incorporation in ergosterol) and bacterial (leucine incorporation) growth rates were investigated at eight seasonal time points during one year. The environmental factors pH and NH4 concentrations explained a larger share of the variation in the microbial community structure. Together they explained 37% of the variation, while season (proxied by temperature) only explained 6% of the variation in PLFA composition. Bacterial and fungal biomass were both highest in early spring, while AM fungal biomass peaked in early summer. Bacterial growth rate, on the other hand, was highest during the autumn, while fungal growth rate showed no clear seasonal pattern. In conclusion, the influence of seasonal variation on microbial communities proved to be relatively small compared to that which could be assigned to pH and NH4 in the studied ranges. (C) 2014 Elsevier Ltd. All rights reserved.
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| 21. |
- Birgander, Johanna, et al.
(författare)
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Temperature adaptation of bacterial growth and C-14-glucose mineralisation in a laboratory study
- 2013
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 65, s. 294-303
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Tidskriftsartikel (refereegranskat)abstract
- Microbial decomposition of soil organic matter (SOM) is the source of most of the terrestrial carbon dioxide emission. Consequently, our ability to predict how climate warming will affect the global carbon (C) budget relies on our understanding of the temperature relationship and adaptability of microbial processes. We exposed soil microcosms to temperatures between 0 and 54 degrees C for 2 months. After this, bacterial growth (leucine incorporation) and functioning (C-14-glucose mineralisation) were estimated at 8 temperatures in the interval 0-54 degrees C to determine temperature relationships and apparent minimum (T-min) and optimum (T-opt) temperatures for growth and mineralisation. We predicted that incubation at temperatures above the initial T-opt for bacteria would select for a warm-adapted community, i.e. a positive shift in T-min and T-opt for bacterial growth, and that this adaptation of the bacterial community would coincide with a similar shift also for their functioning. As anticipated, we found that exposure to temperatures below T-opt did not change the temperature relationship of bacterial growth or mineralisation. Interestingly, T-opt for glucose mineralisation was >20 degrees C higher than that for growth. For bacterial growth, the temperature relationship for the bacterial community was modulated when soils were incubated at temperature above their initial T-opt (approximate to 30 degrees C). This was shown by an increase in T-min of 0.8 degrees C for every 1 degrees C increase in soil temperature, evidencing a shift towards warm-adapted bacteria. Similarly, the Q-10 (15-25 degrees C) for bacterial growth increased at temperature higher than T-opt. We could not detect a corresponding temperature adaptation of the decomposer functioning. We discuss possible underlying reasons for the temperature-responses of bacterial processes. We note that a temperature adaptation will be rapid when exceeding the T-opt, which initially were >20 degrees C higher for glucose mineralisation than growth. This difference could suggest that different responses to warming exposure should be expected for these microbial processes. (C) 2013 Elsevier Ltd. All rights reserved.
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| 22. |
- Birgander, Johanna, et al.
(författare)
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The responses of microbial temperature relationships to seasonal change and winter warming in a temperate grassland
- 2018
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 24:8, s. 3357-3367
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Tidskriftsartikel (refereegranskat)abstract
- Microorganisms dominate the decomposition of organic matter and their activities are strongly influenced by temperature. As the carbon (C) flux from soil to the atmosphere due to microbial activity is substantial, understanding temperature relationships of microbial processes is critical. It has been shown that microbial temperature relationships in soil correlate with the climate, and microorganisms in field experiments become more warm-tolerant in response to chronic warming. It is also known that microbial temperature relationships reflect the seasons in aquatic ecosystems, but to date this has not been investigated in soil. Although climate change predictions suggest that temperatures will be mostly affected during winter in temperate ecosystems, no assessments exist of the responses of microbial temperature relationships to winter warming. We investigated the responses of the temperature relationships of bacterial growth, fungal growth, and respiration in a temperate grassland to seasonal change, and to 2 years’ winter warming. The warming treatments increased winter soil temperatures by 5–6°C, corresponding to 3°C warming of the mean annual temperature. Microbial temperature relationships and temperature sensitivities (Q10) could be accurately established, but did not respond to winter warming or to seasonal temperature change, despite significant shifts in the microbial community structure. The lack of response to winter warming that we demonstrate, and the strong response to chronic warming treatments previously shown, together suggest that it is the peak annual soil temperature that influences the microbial temperature relationships, and that temperatures during colder seasons will have little impact. Thus, mean annual temperatures are poor predictors for microbial temperature relationships. Instead, the intensity of summer heat-spells in temperate systems is likely to shape the microbial temperature relationships that govern the soil-atmosphere C exchange.
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| 23. |
- Birgander, Johanna, et al.
(författare)
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Warmer winters increase the rhizosphere carbon flow to mycorrhizal fungi more than to other microorganisms in a temperate grassland
- 2017
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 23:12, s. 5372-5382
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Tidskriftsartikel (refereegranskat)abstract
- A decisive set of steps in the terrestrial carbon (C) cycle is the fixation of atmospheric C by plants and the subsequent C-transfer to rhizosphere microorganisms. With climate change winters are expected to become milder in temperate ecosystems. Although the rate and pathways of rhizosphere C input to soil could be impacted by milder winters, the responses remain unknown. To address this knowledge-gap, a winter-warming experiment was established in a seminatural temperate grassland to follow the C flow from atmosphere, via the plants, to different groups of soil microorganisms. In situ 13CO2 pulse labelling was used to track C into signature fatty acids of microorganisms. The winter warming did not result in any changes in biomass of any of the groups of microorganisms. However, the C flow from plants to arbuscular mycorrhizal (AM) fungi, increased substantially by winter warming. Saprotrophic fungi also received large amounts of plant-derived C—indicating a higher importance for the turnover of rhizosphere C than biomass estimates would suggest—still, this C flow was unaffected by winter warming. AM fungi was the only microbial group positively affected by winter warming—the group with the closest connection to plants. Winter warming resulted in higher plant productivity earlier in the season, and this aboveground change likely induced plant nutrient limitation in warmed plots, thus stimulating the plant dependence on, and C allocation to, belowground nutrient acquisition. The preferential C allocation to AM fungi was at the expense of C flow to other microbial groups, which were unaffected by warming. Our findings imply that warmer winters may shift rhizosphere C-fluxes to become more AM fungal-dominated. Surprisingly, the stimulated rhizosphere C flow was matched by increased microbial turnover, leading to no accumulation of soil microbial biomass.
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| 24. |
- Brangarí, Albert C., et al.
(författare)
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A soil microbial model to analyze decoupled microbial growth and respiration during soil drying and rewetting
- 2020
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 148
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Tidskriftsartikel (refereegranskat)abstract
- Soils are continuously exposed to cycles of drying and rewetting (D/RW), which drive pronounced fluctuations in soil carbon (C) fluxes. These C dynamics are characterized by a decoupled behavior between microbial biomass synthesis (growth) and CO2 production (respiration). In general, respiration rates peak shortly after RW and subsequently decrease, while the growth peaks lag several hours behind. Despite the significance of these dynamics for the soil C budget and the global C cycle, this feature has so far been overlooked in biogeochemical models and the underlying mechanisms are still unclear. We present a new process-based soil microbial model that incorporates a wide range of physical, chemical and biological mechanisms thought to affect D/RW responses. Results show that the model is able to capture the respiration dynamics in soils exposed to repeated cycles of D/RW, and also to single events in which moisture was kept constant after RW. In addition, the model reproduces, for the first time, the responses of microbial growth to D/RW. We have identified the C accumulation during dry periods, the drought-legacy effect on the synthesis of new biomass, and osmoregulation as the strongest candidate mechanisms to explain these C dynamics. The model outputs are further compared to earlier process-based models, highlighting the advances generated by the new model. This work thus represents a step towards unravelling the microbial responses to drought and rainfall events, with implications for our understanding of C cycle and C sequestration in soils.
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| 25. |
- Brangarí, Albert C., et al.
(författare)
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Soil depth and tillage can characterize the soil microbial responses to drying-rewetting
- 2022
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 173
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of climate on soil microorganisms governs the input and output fluxes of carbon (C) from soils. The study of the drastic responses to drying-rewetting offers an opportunity to assess an aspect of ‘soil health’ via evaluating the role of microbes in soil biochemistry and C cycling. Recent evidence has consistently shown that communities exposed to extreme moisture fluctuations recurrently can better cope with the stress generated by them and exhibit a ‘resilient’ microbial response after rewetting (fast recovery of microbial communities to the pre-disturbance growth levels), whereas otherwise they show a more ‘sensitive’ response (slow recovery). However, it is still not known if land-use management can alter these responses. In this study, we investigated this issue by performing a drying-rewetting experiment on soil samples from two land-uses (permanent pastures and tilled croplands) and two depths (0–5 cm and 20–30 cm), and measured bacterial growth, fungal growth, and respiration at high temporal resolution. We then derived a series of indicators of soil health based on the characteristics of these microbial responses to drying-rewetting. Results showed categorically different patterns in soils from pastures and croplands, confirming the capacity of land use to change soil functioning. Tillage practices cancelled the stratification in the top 30 cm of soil and increased the exposure and adaptation of soil microorganisms to conditions of water stress, which caused shifts in the microbial responses to drying-rewetting. The sensitive patterns in bacterial growth found in undisturbed pastures were replaced by resilient responses in both shallow and deep croplands. Fungi showed a tendency for faster recoveries in croplands but patterns were consistently resilient in all sites and depths, indicating that fungi were little affected by land-use-induced dis- turbances. Respiration exhibited resilient-like responses in shallow samples, but in depth, they were sensitive in pastures and resilient in croplands. We also observed an alternated sequence of bacterial and fungal growth over time that suggested competition and different strategies of reactivation after rewetting by the two types of microorganisms.
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| 26. |
- Brangarí, Albert C., et al.
(författare)
-
The mechanisms underpinning microbial resilience to drying and rewetting - A model analysis
- 2021
-
Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 162
-
Tidskriftsartikel (refereegranskat)abstract
- Soil moisture is one of the most important factors controlling the activity and diversity of soil microorganisms. Soils exposed to pronounced cycles of drying and rewetting (D/RW) exhibit disconnected patterns in microbial growth and respiration at RW. These patterns differ depending on the preceding soil moisture history, leading to contrasting amounts of carbon retained in the soil as biomass versus that respired as CO2. The mechanisms underlying these microbially-induced dynamics are still unclear. In this work, we used the process-based soil microbial model EcoSMMARTS to offer candidate explanations for: i) how soil moisture can shape the structure of microbial communities, ii) how soil moisture history affects the responses during D/RW, iii) what microbial mechanisms control the shape, intensity and duration of these responses, and iv) what carbon sources sustain the increased biogeochemical rates after RW. We first evaluated the response to D/RW in bacterial communities previously exposed to two different stress histories (‘moderate’ vs ‘severe’ soil moisture regimes). We found that both the history of soil moisture and the harshness of the dry period preceding the rewetting shaped the structure and physiology of microbial communities. The characteristics of these communities determined the harshness experienced and the nature of the responses to RW obtained. Modelled communities exposed to extended severe conditions showed a resilient response to D/RW, whereas those exposed to moderate environments exhibited a more sensitive response. We then interchanged the soil moisture regimes and found that the progressive adaptation of microbial physiology and structure to new environmental conditions resulted in a switch in the response patterns. These microbial changes also determined the contribution of biomass synthesis, osmoregulation, mineralization by cell residues, and disruption of soil aggregates to CO2 emissions.
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| 27. |
- Cordero, Irene, et al.
(författare)
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High intensity perturbations induce an abrupt shift in soil microbial state
- 2023
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Ingår i: ISME Journal. - 1751-7362. ; 17:12, s. 2190-2199
-
Tidskriftsartikel (refereegranskat)abstract
- Soil microbial communities play a pivotal role in regulating ecosystem functioning. But they are increasingly being shaped by human-induced environmental change, including intense “pulse” perturbations, such as droughts, which are predicted to increase in frequency and intensity with climate change. While it is known that soil microbial communities are sensitive to such perturbations and that effects can be long-lasting, it remains untested whether there is a threshold in the intensity and frequency of perturbations that can trigger abrupt and persistent transitions in the taxonomic and functional characteristics of soil microbial communities. Here we demonstrate experimentally that intense pulses of drought equivalent to a 30-year drought event (<15% WHC) induce a major shift in the soil microbial community characterised by significantly altered bacterial and fungal community structures of reduced complexity and functionality. Moreover, the characteristics of this transformed microbial community persisted after returning soil to its previous moisture status. As a result, we found that drought had a strong legacy effect on bacterial community function, inducing an enhanced growth rate following subsequent drought. Abrupt transitions are widely documented in aquatic and terrestrial plant communities in response to human-induced perturbations. Our findings demonstrate that such transitions also occur in soil microbial communities in response to high intensity pulse perturbations, with potentially deleterious consequences for soil health.
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| 28. |
- Cruz-Paredes, Carla, et al.
(författare)
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Can moisture affect temperature dependences of microbial growth and respiration?
- 2021
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 156
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Tidskriftsartikel (refereegranskat)abstract
- It is of great importance to understand how terrestrial ecosystems will respond to global changes. However, most experimental approaches have focused on single factors. In natural systems, moisture and temperature often change simultaneously, and they can interact and shape microbial responses. Even though soil moisture and temperature are very important factors controlling microbial activity, there is disagreement on the dependence of microbial rates on temperature and moisture as well as their sensitivity when both variables change simultaneously. Here we created a moisture gradient and determined high resolution intrinsic temperature dependences for bacterial and fungal growth rates as well as respiration rates. We found that microbial rates decreased with lower moisture and increased with higher temperatures until optimum values. Additionally, we found independence between temperature and moisture as rate modifiers. We also found that temperature sensitivities (Q10) for microbial growth and respiration were not affected by changes in moisture. This provided an experimental framework to validate assumptions of temperature and moisture rate modifiers used in ecosystem and global cycling models (GCMs).
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| 29. |
- Cruz-Paredes, Carla, et al.
(författare)
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Controls of microbial carbon use efficiency along a latitudinal gradient across Europe
- 2024
-
Ingår i: Soil Biology and Biochemistry. - 0038-0717. ; 193
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Tidskriftsartikel (refereegranskat)abstract
- Microbial carbon use efficiency (CUE) describes the partitioning of carbon (C) between respiration and growth, and this defines the soil-atmosphere C balance. Despite its importance, CUE is not properly represented in soil biogeochemical models. Here, we estimated how CUE varied in soil along a continental gradient. Through a structural equation model, we found that bacterial growth, fungal community composition, and SOM quality were the main drivers of CUE variation. Biotic factors controlled CUE directly, while soil properties and climate indirectly controlled CUE via biotic factors. Surprisingly, we found that microbial assimilability of SOM had a negative relationship with CUE. High rates of microbial SOM-use coincided with a greater growth-fraction used for respiration suggesting decoupled catabolism and anabolism, probably due to nutrient limitation. Our study highlights the importance of the microbial community composition to predict CUE and that interactions between bacterial and fungal communities can have implications for CUE.
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| 30. |
- Cruz-Paredes, Carla, et al.
(författare)
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Using community trait-distributions to assign microbial responses to pH changes and Cd in forest soils treated with wood ash
- 2017
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 112, s. 153-164
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Tidskriftsartikel (refereegranskat)abstract
- The identification of causal links between microbial community structure and ecosystem functions are required for a mechanistic understanding of ecosystem responses to environmental change. One of the most influential factors affecting plants and microbial communities in soil in managed ecosystems is the current land-use. In forestry, wood ash has been proposed as a liming agent and a fertilizer, but has been questioned due to the risk associated with its Cd content. The aim of this study was to determine the effects of wood ash on the structure and function of decomposer microbial communities in forest soils and to assign them to causal mechanisms. To do this, we assessed the responses to wood ash application of (i) the microbial community size and structure, (ii) microbial community trait-distributions, including bacterial pH relationships and Cd-tolerance, to assign the microbial responses to pH and Cd, and (iii) consequences for proxies of the function soil organic matter (SOM) turnover including respiration and microbial growth rates. Two sets of field-experiments in temperate conifer forest plantations were combined with laboratory microcosm experiments where wood ash additions were compared to additions of lime and Cd. Wood ash induced structural changes in the microbial community in both field experiments, and striking similarities were observed between the application of ash and that of lime in the microcosm experiments. Wood ash increased pH, and led to a shift toward faster SOM decomposition and a reduced importance of fungi. This coincided with shifts in bacterial community trait distributions for pH, with pH optima closely tracking the new soil pH. A Cd solution could induce Cd-tolerance in the microcosm experiments, but the ash did not affect the microbial tolerance to Cd in field or microcosm experiments. We demonstrate that the microbial community responded strongly to the application of wood ash to forest soils with consequences for its functional capabilities in terms of respiration and growth rates. The bacterial community's trait distributions revealed that the increased pH directly caused the microbial responses, while the wood ash associated Cd has no detectable effects on the microbial community. The study demonstrates the power of community trait distributions to (i) causally link microbial structural responses to environmental change and (ii) potential to predict the ecosystem functional consequences.
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| 31. |
- Cruz-Paredes, Carla, et al.
(författare)
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Variation in Temperature Dependences across Europe Reveals the Climate Sensitivity of Soil Microbial Decomposers
- 2023
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Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 89:5, s. 0209022-0209022
-
Tidskriftsartikel (refereegranskat)abstract
- Temperature is a major determinant of biological process rates, and microorganisms are key regulators of ecosystem carbon (C) dynamics. Temperature controls microbial rates of decomposition, and thus warming can stimulate C loss, creating positive feedback to climate change. If trait distributions that define temperature relationships of microbial communities can adapt to altered temperatures, they could modulate the strength of this feedback, but if this occurs remains unclear. In this study, we sampled soils from a latitudinal climate gradient across Europe. We established the temperature relationships of microbial growth and respiration rates and used these to investigate if and with what strength the community trait distributions for temperature were adapted to their local environment. Additionally, we sequenced bacterial and fungal amplicons to link the variance in community composition to changes in temperature traits. We found that microbial temperature trait distributions varied systematically with climate, suggesting that an increase in mean annual temperature (MAT) of 1°C will result in warm-shifted microbial temperature trait distributions equivalent to an increase in temperature minimum (Tmin) of 0.20°C for bacterial growth, 0.07°C for fungal growth, and 0.10°C for respiration. The temperature traits for bacterial growth were thus more responsive to warming than those for respiration and fungal growth. The microbial community composition also varied with temperature, enabling the interlinkage of taxonomic information with microbial temperature traits. Our work shows that the adaptation of microbial temperature trait distributions to a warming climate will affect the C-climate feedback, emphasizing the need to represent this to capture the microbial feedback to climate change. IMPORTANCE One of the largest uncertainties of global warming is if the microbial decomposer feedback will strengthen or weaken soil C-climate feedback. Despite decades of research effort, the strength of this feedback to warming remains unknown. We here present evidence that microbial temperature relationships vary systematically with environmental temperatures along a climate gradient and use this information to forecast how microbial temperature traits will create feedback between the soil C cycle and climate warming. We show that the current use of a universal temperature sensitivity is insufficient to represent the microbial feedback to climate change and provide new estimates to replace this flawed assumption in Earth system models. We also demonstrate that temperature relationships for rates of microbial growth and respiration are differentially affected by warming, with stronger responses to warming for microbial growth (soil C formation) than for respiration (C loss from soil to atmosphere), which will affect the atmosphere-land C balance.
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| 32. |
- de Nijs, Evy A., et al.
(författare)
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Soil microbial moisture dependences and responses to drying–rewetting : The legacy of 18 years drought
- 2019
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 25:3, s. 1005-1015
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Tidskriftsartikel (refereegranskat)abstract
- Climate change will alter precipitation patterns with consequences for soil C cycling. An understanding of how fluctuating soil moisture affects microbial processes is therefore critical to predict responses to future global change. We investigated how long-term experimental field drought influences microbial tolerance to lower moisture levels (“resistance”) and ability to recover when rewetted after drought (“resilience”), using soils from a heathland which had been subjected to experimental precipitation reduction during the summer for 18 years. We tested whether drought could induce increased resistance, resilience, and changes in the balance between respiration and bacterial growth during perturbation events, by following a two-tiered approach. We first evaluated the effects of the long-term summer drought on microbial community functioning to drought and drying–rewetting (D/RW), and second tested the ability to alter resistance and resilience through additional perturbation cycles. A history of summer drought in the field selected for increased resilience but not resistance, suggesting that rewetting after drought, rather than low moisture levels during drought, was the selective pressure shaping the microbial community functions. Laboratory D/RW cycles also selected for communities with a higher resilience rather than increased resistance. The ratio of respiration to bacterial growth during D/RW perturbation was lower for the field drought-exposed communities and decreased for both field treatments during the D/RW cycles. This suggests that cycles of D/RW also structure microbial communities to respond quickly and efficiently to rewetting after drought. Our findings imply that microbial communities can adapt to changing climatic conditions and that this might slow the rate of soil C loss predicted to be induced by future cyclic drought.
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| 33. |
- Donhauser, Johanna, et al.
(författare)
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Temperatures beyond the community optimum promote the dominance of heat-adapted, fast growing and stress resistant bacteria in alpine soils
- 2020
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 148
-
Tidskriftsartikel (refereegranskat)abstract
- Alpine soils are warming strongly, leading to profound alterations in carbon cycling and greenhouse gas budgets, mediated via the soil microbiome. To explore microbial responses to global warming, we incubated eight alpine soils between 4 and 35 °C and linked the temperature dependency of bacterial growth with alterations in community structures and the identification of temperature sensitive taxa. The temperature optimum for bacterial growth was between 27 and 30 °C and was higher in soils from warmer environments. This temperature framing the upper limit of naturally occurring temperatures was a tipping point above which the temperature range for growth shifted towards higher temperatures together with pronounced changes in community structures and diversity based on both 16S rRNA gene and transcript sequencing. For instance, at the highest temperature, we observed a strong increase in OTUs affiliated with Burkholderia-Paraburkholderia, Phenylobacterium, Pseudolabrys, Edaphobacter and Sphingomonas. Dominance at high temperature was explained by a priori adaptation to high temperature, high growth potential as well as stress resistance. At the highest temperature, we moreover observed an overall increase in copiotrophic properties in the community along with high growth rates. Further, temperature effects on community structures depended on the long-term climatic legacy of the soils. These findings contribute to extrapolating from single to multiple sites across a large range of conditions.
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| 34. |
- Fernández-Calviño, David, et al.
(författare)
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Ecotoxicological assessment of propiconazole using soil bacterial and fungal growth assays
- 2017
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Ingår i: Applied Soil Ecology. - : Elsevier BV. - 0929-1393. ; 115, s. 27-30
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Tidskriftsartikel (refereegranskat)abstract
- Effects of the fungicide propiconazole on soil microorganisms were tested using [3H] leucine incorporation and [14C] acetate in ergosterol incorporation to measure bacterial and fungal growth inhibition, respectively. Growth was compared to basal respiration (BR) and substrate-induced respiration (SIR) in soil microcosms established according to the OECD 217 guideline. Fungal growth was most sensitive with IC50 values remaining around 300 mg kg−1 during 40 days of incubation. SIR was initially less sensitive (IC50 1300 mg kg−1), but IC50 values progressively decreased over time to reach 380 mg kg−1 after 40 days. Bacterial growth was affected at concentrations ≥200 mg kg−1, but exhibited more complex dose-response relationships possibly due to a combination of direct toxicity, bacterial community adaptation, and competitive release from the more severely affected fungi. BR was either stimulated or not affected by propiconazole. Our results indicate that group-specific endpoints targeting microbial growth will improve ecotoxicological assessment of toxicants for environmental risk assessment.
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| 35. |
- Fernández-Calviño, David, et al.
(författare)
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Isothiazolinone inhibition of soil microbial activity persists despite biocide dissipation
- 2023
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 178
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Tidskriftsartikel (refereegranskat)abstract
- Soil microbial growth and activity are generally assumed to recover rapidly after dissipation of organic toxicants. We studied the effects of four readily degradable isothiazolinone biocides (benzisothiazolinone, BIT; methylisothiazolinone, MIT; octylisothiazolinone, OIT; 4,5-dichloro-2-octyl-isothiazolinone, DCOIT) on bacterial growth, fungal growth, basal respiration, and substrate-induced respiration in controlled soil microcosm experiments. Bacterial growth followed by fungal growth were the two most sensitive endpoints during the first two days. Significant dissipation of biocides occurred within just 8 h and 94–100% had dissipated after 40 days except for DCOIT tested at a high concentration (50 mg kg−1, 54% remaining after 40 d). Despite biocide dissipation, all isothiazolinones inhibited bacterial growth for >7 days, whereas fungal growth and substrate-induced respiration were inhibited for up to 40 days. Bacterial growth recovery after 40 days was linked to development of bacterial community tolerance for DCOIT, but not for the other less persistent isothiazolinones. Our study is the first to report on toxic effects of isothiazolinones on soil microbial growth and demonstrates that inhibitory effects of isothiazolinones on soil microbial growth and activity (especially fungal growth and substrate-induced respiration) persisted even long after biocide dissipation, indicating “legacy effects” and retarded recovery of soil microbial functions. We propose that retarded recovery of fungal, relative to bacterial, growth may be a general phenomenon during the dissipation of toxicants in contaminated soils and that it may be explained by intrinsic differences between bacterial and fungal biology in soil and by competitive interactions between these two dominant groups of soil microbial decomposers.
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| 36. |
- Fernández-Calviño, David, et al.
(författare)
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Short-term toxicity assessment of a triazine herbicide (terbutryn) underestimates the sensitivity of soil microorganisms
- 2021
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 154
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Tidskriftsartikel (refereegranskat)abstract
- Little is known about the impacts of persistent triazine herbicides and biocides on soil microorganisms. Terbutryn toxicity in soil microorganisms was studied using bacterial and fungal growth, substrate induced respiration (SIR) and basal respiration as ecotoxicological end-points. In the short-term (0–7 days), increasing concentrations of terbutryn (0–800 mg kg−1) progressively inhibited bacterial and fungal growth by up to 33–36% (4 h) and 49–55% (7 days), whereas SIR and basal soil respiration remained unaffected. Following long-term (40 days) exposure to terbutryn, both bacterial and fungal growth were inhibited by up to 76–78%, and SIR was inhibited by up to 53%. Hence, our results unexpectedly demonstrate time-cumulative microbial growth inhibition over extended time periods in soil and indicate that current ecotoxicological guidelines may underestimate risks posed by chemicals to soil microorganisms.
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| 37. |
- Fernández-Calviño, David, et al.
(författare)
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Using pine bark and mussel shell amendments to reclaim microbial functions in a Cu polluted acid mine soil
- 2018
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Ingår i: Applied Soil Ecology. - : Elsevier BV. - 0929-1393. ; 127, s. 102-111
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Tidskriftsartikel (refereegranskat)abstract
- An extremely acid mine soil polluted with Cu was amended with pine bark, crushed mussel shell or a 1:1 mixture of these two by-products. The performance of the soil microbial community was measured as the bacterial and fungal community growth, which were monitored during 2 years following the amendments. Pine bark caused significant increases of microbial growth rates, but with distinct differences between fungal and bacterial groups. Bacterial growth increased transiently at intermediate rates of pine bark applications, but returned to control rates within 2 years of application. In contrast, pine bark applications consistently increased fungal growth with effects that were maintained throughout the study period. The addition of only crushed mussel shell to the mine soil caused very delayed positive effects on the bacterial growth and almost no significant effects on the fungal growth. However, the combination of pine bark with crushed mussel shells 1:1 mixtures caused positive growth responses of both bacteria and fungi that remained persistent throughout the 2 years of study. Fungal and bacterial growth were both suppressed in the mine soil by the lack of organic matter. In addition, bacterial growth was also secondarily suppressed by acidity, and hence, when organic matter (pine bark) additions were combined with pH increases (crushed mussel shell additions), bacterial growth was additionally stimulated. In conclusion, the proposed mixture of by-products (pine bark and crushed mussel shell) is suggested as a promising reclamation strategy for acid mine soils. These results also suggest that in soils like that studied here the organic matter limitation is a more important factor than the soil pH and Cu availability for fungal and bacterial performance.
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| 38. |
- Fernandez-Lopez, David, et al.
(författare)
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Bacterial pH-optima for growth track soil pH, but are higher than expected at low pH
- 2011
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 43:7, s. 1569-1575
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Tidskriftsartikel (refereegranskat)abstract
- One of the most influential factors determining the growth and composition of soil bacterial communities is pH. However, soil pH is often correlated with many other factors, including nutrient availability and plant community, and causality among factors is not easily determined. If soil pH is directly influencing the bacterial community, this must lead to a bacterial community growth optimised for the in situ pH. Using one set of Iberian soils (46 soils covering pH 4.2-7.3) and one set of UK grassland soils (16 soils covering pH 3.3-7.5) we measured the pH-optima for the growth of bacterial communities. Bacterial growth was estimated by the leucine incorporation method. The pH-optima for bacterial growth were positively correlated with soil pH, demonstrating its direct influence on the soil bacterial community. We found that the pH from a water extraction better matched the bacterial growth optimum compared with salt extractions of soil. Furthermore, we also showed a more subtle pattern between bacterial pH growth optima and soil pH. While closely matched at neutral pHs, pH-optima became higher than the in situ pH in more acid soils, resulting in a difference of about one pH-unit at the low-pH end. We propose that an explanation for the pattern is an interaction between increasing overall bacterial growth with higher pHs and the unimodal pH-response for growth of bacterial communities. (C) 2011 Elsevier Ltd. All rights reserved.
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| 39. |
- Ford, H., et al.
(författare)
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Grazing effects on microbial community composition, growth and nutrient cycling in salt marsh and sand dune grasslands
- 2013
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Ingår i: Biology and Fertility of Soils. - : Springer Science and Business Media LLC. - 0178-2762 .- 1432-0789. ; 49:1, s. 89-98
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Tidskriftsartikel (refereegranskat)abstract
- The effect of grazing by large herbivores on the microbial community and the ecosystem functions they provide are relatively unknown in grassland systems. In this study, the impact of grazing upon the size, composition and activity of the soil microbial community was measured in field experiments in two coastal ecosystems: one salt marsh and one sand dune grassland. Bacterial, fungal and total microbial biomass were not systematically affected by grazing across ecosystems, although, within an ecosystem, differences could be detected. Fungal-to-bacterial ratio did not differ with grazing for either habitat. Redundancy analysis showed that soil moisture, bulk density and root biomass significantly explained the composition of phospholipid fatty acid (PLFA) markers, dominated by the distinction between the two grassland habitats, but where the grazing effect could also be resolved. PLFA markers for Gram-positive bacteria were more proportionally abundant in un-grazed, and markers for Gram-negative bacteria in grazed grasslands. Bacterial growth rate (leucine incorporation) was highest in un-grazed salt marsh but did not vary with grazing intensity in the sand dune grassland. We conclude that grazing consistently affects the composition of the soil microbial community in semi-natural grasslands but that its influence is small (7 % of the total variation in PLFA composition), compared with differences between grassland types (89 %). The relatively small effect of grazing translated to small effects on measurements of soil microbial functions, including N and C mineralisation. This study is an early step toward assessing consequences of land-use change for global nutrient cycles driven by the microbial community.
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| 40. |
- García-Palacios, Pablo, et al.
(författare)
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Evidence for large microbial-mediated losses of soil carbon under anthropogenic warming
- 2021
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Ingår i: Nature Reviews Earth and Environment. - : Springer Science and Business Media LLC. - 2662-138X. ; 2:7, s. 507-517
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Forskningsöversikt (refereegranskat)abstract
- Anthropogenic warming is expected to accelerate global soil organic carbon (SOC) losses via microbial decomposition, yet, there is still no consensus on the loss magnitude. In this Perspective, we argue that, despite the mechanistic uncertainty underlying these losses, there is confidence that a strong, positive land carbon–climate feedback can be expected. Two major lines of evidence support net global SOC losses with warming via increases in soil microbial metabolic activity: the increase in soil respiration with temperature and the accumulation of SOC in low mean annual temperature regions. Warming-induced SOC losses are likely to be of a magnitude relevant for emission negotiations and necessitate more aggressive emission reduction targets to limit climate change to 1.5 °C by 2100. We suggest that microbial community–temperature interactions, and how they are influenced by substrate availability, are promising research areas to improve the accuracy and precision of the magnitude estimates of projected SOC losses.
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| 41. |
- Glanville, H., et al.
(författare)
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Mineralization of low molecular weight carbon substrates in soil solution under laboratory and field conditions
- 2012
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 48, s. 88-95
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Tidskriftsartikel (refereegranskat)abstract
- A more detailed mechanistic understanding of how low molecular weight (MW) carbon (C) substrates are mineralized within the rhizosphere by soil microbial communities is crucial to accurately model terrestrial C fluxes. Currently, most experiments regarding soil C dynamics are conducted ex-situ (laboratory) and can fail to account for key variables (e.g. temperature and soil water content) which vary in-situ. In addition, ex-situ experiments are often highly invasive, e.g. severing root and mycorrhizal networks, changing the input and concentrations of low MW exudates within soil. The aim of this study was to directly compare the mineralization rates of 31 common low MW C substrates under ex- and in-situ conditions. In addition, we also assessed the inter-annual field variability of substrate mineralization rates. We added trace concentrations of 31 individual C-14-labelled common low MW C substrates into the top soil of an agricultural grassland and monitored the mineralization rates by capturing (CO2)-C-14 evolved from the soil over 7 d. Our results showed that the contribution of low MW C components to soil respiration was highly reproducible between parallel studies performed either in-situ or ex-situ. We also found that differences in the mineralization of individual compounds were more variable inter-annually in the field than between the laboratory and the field. Our results suggest that laboratory-based C mineralization data can be used to reliably parameterize C models but that multiple experimental measurements should be made over time to reduce uncertainty in model parameter estimation. (C) 2012 Elsevier Ltd. All rights reserved.
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| 42. |
- Göransson, Hans, et al.
(författare)
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Bacterial growth and respiration responses upon rewetting dry forest soils: Impact of drought-legacy
- 2013
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 57, s. 477-486
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Tidskriftsartikel (refereegranskat)abstract
- Longer periods of drought and droughts of higher intensity are expected to become increasingly frequent with future climate change. This has implications for the microbially mediated turnover of soil organic matter (SOM), which will feedback to the global C cycle. In this study, we addressed the microbial dynamics underlying the pulse of respiration following rewetting of dry soil, and how the drought-legacy of the soil modulated this response. We studied the microbial dynamics upon rewetting of dry soils from a field-experiment in a temperate forest soil exposed to two seasons of experimental summer-drought, or ambient conditions, by rewetting air-dried soil samples, and monitoring the respiration and bacterial growth responses. The respiratory responses in drought-exposed soils were slower and reached lower rates than control soils, translating to less C mineralised one week after rewetting. While the bacterial growth in drought-exposed soil also was slower, this was only a delayed response, and no differences in cumulative bacterial growth one week after rewetting could be established between drought-exposed and control soils. The pulse in respiration and microbial growth following the rewetting appeared to be due to facilitated microbial C availability caused by physical perturbation of the soil induced by the rewetting event. Reduced C input by trees during drought probably contributed to differences between drought-treated and control soils. Our results indicate that a history of drought increases the microbial C-use efficiency during a rewetting, suggesting a negative feedback to climate warming.
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| 43. |
- Haei, Mahsa, et al.
(författare)
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Effects of soil frost on growth, composition and respiration of the soil microbial decomposer community
- 2011
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 43:10, s. 2069-2077
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Tidskriftsartikel (refereegranskat)abstract
- Most climate change scenarios predict that the variability of weather conditions will increase in coming decades. Hence, the frequency and intensity of freeze-thaw cycles in high-latitude regions are likely to increase, with concomitant effect on soil carbon biogeochemistry and associated microbial processes. To address this issue we sampled riparian soil from a Swedish boreal forest and applied treatments with variations in four factors related to soil freezing (temperature, treatment duration, soil water content and frequency of freeze-thaw cycles), at three levels in a laboratory experiment, using a Central Composite Face-centred (CCF) experimental design. We then measured bacterial (leucine incorporation) and fungal (acetate in ergosterol incorporation) growth, basal respiration, soil microbial phospholipid fatty acid (PLFA) composition, and concentration of dissolved organic carbon (DOC). Fungal growth was higher in soil exposed to freeze-thawing perturbations and freezing temperatures of -6 degrees C and -12 degrees C, than under more constant conditions (steady 0 degrees C). The opposite pattern was found for bacteria, resulting in an increasing fungal-to-bacterial growth ratio following more intensive winter conditions. Soil respiration increased with water content, decreased with treatment duration and appeared to mainly be driven by treatment-induced changes in the DOC concentration. There was a clear shift in the PLFA composition at 0 degrees C, compared with the two lower temperatures, with PLFA markers associated with fungi as well as a number of unsaturated PLFAs being relatively more common at 0 degrees C. Shifts in the PLFA pattern were consistent with those expected for phenotypic plasticity of the cell membrane to low temperatures. There were small declines in PLFA concentrations after freeze-thawing and with longer durations. However, the number of freeze-thaw events had no effect on the microbiological variables. The findings suggest that the higher frequency of freeze-thaw events predicted to follow the global warming will likely have a limited impact on soil microorganisms. (C) 2011 Elsevier Ltd. All rights reserved.
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| 44. |
- Heděnec, Petr, et al.
(författare)
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Mycorrhizal association of common European tree species shapes biomass and metabolic activity of bacterial and fungal communities in soil
- 2020
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 149
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Tidskriftsartikel (refereegranskat)abstract
- Recent studies have revealed effects of various tree species on soil physical and chemical properties. However, effects of various tree species on composition and activity of soil microbiota and the relevant controls remain poorly understood. We evaluated the influence of tree species associated with two different mycorrhizal types, ectomycorrhiza (EcM) and arbuscular mycorrhiza (AM), on growth, biomass and metabolic activity of soil fungal and bacterial communities using common garden tree species experiments throughout Denmark. The soil microbial communities differed between six European tree species as well as between EcM (beech, lime, oak and spruce) and AM (ash and maple) tree species. The EcM tree species had higher fungal biomass, fungal growth and bacterial biomass, while AM species showed higher bacterial growth. The results indicated that microbial community composition and functioning differed between groups of tree species with distinct litter qualities that generate soil C/N ratio and soil pH differences. The mycorrhizal association only partly explained litter quality and soil microbial species differences since lime was more similar to AM tree species. In addition, our results indicated that tree species-mediated soil pH and C/N ratio were the most important variables shaping microbial communities with a positive effect on bacterial and a negative effect on fungal growth rates. The results suggest that tree species-mediated microbial community composition and activity may be important drivers of the different vertical soil C distribution previously observed in AM and EcM tree species.
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| 45. |
- Heděnec, Petr, et al.
(författare)
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Tree species, mycorrhizal associations, and land-use history as drivers of cohesion in soil biota communities and microbe-fauna interactions
- 2024
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Ingår i: Forest Ecology and Management. - 0378-1127. ; 560
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Tidskriftsartikel (refereegranskat)abstract
- Community cohesion is a recent concept in ecology referring to the varying levels of connectivity and integration between populations of different taxonomic or functional groups within ecosystems. Positive cohesion denotes positive interactions such as mutualism or facilitation, while negative cohesion implies negative interactions such as competitive exclusion or a preference for different habitats. However, the effects of ecosystem characteristics such as tree species identity, mycorrhizal association and land-use history on soil biota community cohesion and microbe-fauna interactions remains poorly understood. We analyzed data on soil microbial biomass and biomass of taxonomic and functional groups of soil fauna obtained from monoculture stands of broadleaved tree species (maple and ash) associated with arbuscular mycorrhiza (AM), broadleaved tree species (beech, lime, and oak) associated with ectomycorrhizal fungi (ECM) and coniferous Norway spruce associated with ECM planted in common garden designs on former cropland and former forest land across Denmark. Our results revealed both positive and negative cohesion within soil communities, with only negative cohesion varying significantly among tree species. Soil biota communities under spruce indicated the most negative cohesion, whereas maple and ash soils showed least negative cohesion. Community cohesion varied across different sampling locations and between sites with different land-use histories. Positive cohesion was more pronounced in former cropland than in former old forest land, while negative cohesion was more pronounced in soils under tree species associated with ECM fungi than in soils beneath tree species associated with AM fungi. Both positive and negative cohesion were strongly influenced by litter chemistry and soil properties, indicating complex ecological dynamics. Soil pH, litter decomposition indices, and soil C:N ratio emerged as key drivers of microbial and faunal community structures. Additionally, the total microbial and faunal biomass, as well as the community structure of soil microbial and faunal communities, indicated strong positive interactions. Our results have the potential to support forest management by aiding in the selection of suitable tree species to support different groups of soil microbes and fauna, which play crucial role in ecosystem services such as nutrient release and transformation of soil organic matter.
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| 46. |
- Heděnec, Petr, et al.
(författare)
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Tree species traits and mycorrhizal association shape soil microbial communities via litter quality and species mediated soil properties
- 2023
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Ingår i: Forest Ecology and Management. - : Elsevier BV. - 0378-1127. ; 527
-
Tidskriftsartikel (refereegranskat)abstract
- Soils harbor a vast diversity of soil microbiota, which play a crucial role in key ecosystem processes such as litter transformation and mineralization, but how complex plant-soil interactions shape the diversity and composition of soil microbiota remains elusive. We performed amplicon sequencing of DNA isolated from mineral topsoil of six common European trees planted in multi-site common garden monoculture stands of broadleaved maple and ash associated with arbuscular mycorrhiza (AM), broadleaved beech, lime and oak associated with ectomycorrhizal fungi (ECM) and coniferous spruce associated with ECM. The main aim of this study was to evaluate the effects of tree species identity, traits and mycorrhizal associations on diversity, community structure, cohesion, and shift in the relative abundance of taxonomic and functional groups of soil bacteria, fungi and nematodes. Our results revealed that soils beneath broadleaved trees hosted higher OTU richness of bacteria, fungi, and nematodes than under Norway spruce. Broadleaved tree species associated with AM fungi showed higher cohesion of bacterial and fungal communities than broadleaved trees associated with ECM fungi, but the cohesion of nematode communities was higher under trees associated with ECM fungi than under trees associated with AM fungi. Copiotrophic bacteria, fungal saprotrophs and bacterivorous nematodes were associated with ash, maple and lime having high soil pH, and high litter decomposition indices, while oligotrophic bacteria, ectomycorrhizal fungi and fungivorous nematodes were associated with beech, oak and Norway spruce that had low soil pH and low litter decomposition indices. Tree species associated with AM fungi had a high proportion of copiotrophic bacteria and saprotrophic fungi while trees associated with ECM fungi showed a high relative abundance of oligotrophic bacteria, ECM fungi and fungivorous nematodes. The different abundances of these functional groups support the more inorganic nutrient economy of AM tree species vs the more organic dominated nutrient economy of ECM tree species. The bacterial community was indirectly affected by litter quality via soil properties, while the fungal community was directly affected by litter quality and tree species. The functional groups of nematodes mirrored the communities of bacteria and fungi, thereby indicating the main and active groups of the tree species-specific microbial communities. Our study suggested that tree species identity, traits, and mycorrhizal association substantially shape microbial communities via a direct effect of litter chemistry as well as via litter-mediated soil properties.
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| 47. |
- Hicks, Lettice C., et al.
(författare)
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Bacteria constrain the fungal growth response to drying-rewetting
- 2019
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 134, s. 108-112
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Tidskriftsartikel (refereegranskat)abstract
- Bacteria and fungi are the two principal decomposer groups in soils, determining rates of biogeochemical cycling. Rewetting of dry soils induces enormous dynamics in biogeochemistry. Bacteria have been shown to exhibit large variation in growth over time upon drying-rewetting (D/RW), however, in studies to date, fungal growth has shown limited responsiveness. Here we investigated whether fungal growth responses to D/RW are constrained by competition with bacteria by using the bactericide bronopol to suppress bacterial growth during D/RW. We examined responses for two different soils, previously shown to exhibit different bacterial growth responses to D/RW. Experimental elimination of bacterial growth lead to increased fungal growth in both soils upon D/RW, indicating a competitive release of fungal growth when bacteria were suppressed. We also observed a pronounced fungal growth response to D/RW for one of the soils, which has not been previously reported. In this case, even when rewetting with water (i.e. without bacterial suppression), fungal growth increased to reach rates 10-times greater than in the moist control soil. The peak in fungal growth coincided with a secondary peak of respiration, revealing a functional importance of fungi for C-cycling during D/RW. The decline in fungal growth following this peak also coincided with the onset of exponential bacterial growth, further strengthening evidence for a negative correlation between bacteria and fungi, suggesting that competition with bacteria can constrain the fungal growth response to D/RW.
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| 48. |
- Hicks, Lettice C., et al.
(författare)
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Nutrient limitation may induce microbial mining for resources from persistent soil organic matter
- 2021
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 102:6
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Tidskriftsartikel (refereegranskat)abstract
- Fungi and bacteria are the two principal microbial groups in soil, responsible for the breakdown of organic matter (OM). The relative contribution of fungi and bacteria to decomposition is thought to impact biogeochemical cycling at the ecosystem scale, whereby bacterially dominated decomposition supports the fast turnover of easily available substrates, whereas fungal-dominated decomposition leads to the slower turnover of more complex OM. However, empirical support for this is lacking. We used soils from a detritus input and removal treatment experiment in an old-growth coniferous forest, where above- and belowground litter inputs have been manipulated for 20 yr. These manipulations have generated variation in OM quality, as defined by energetic content and proxied as respiration per g soil organic matter (SOM) and the δ13C signature in respired CO2 and microbial PLFAs. Respiration per g SOM reflects the availability and lability of C substrate to microorganisms, and the δ13C signature indicates whether the C used by microorganisms is plant derived and higher quality (more δ13C depleted) or more microbially processed and lower quality (more δ13C enriched). Surprisingly, higher quality C did not disproportionately benefit bacterial decomposers. Both fungal and bacterial growth increased with C quality, with no systematic change in the fungal-to-bacterial growth ratio, reflecting the relative contribution of fungi and bacteria to decomposition. There was also no difference in the quality of C targeted by bacterial and fungal decomposers either for catabolism or anabolism. Interestingly, respired CO2 was more δ13C enriched than soil C, suggesting preferential use of more microbially processed C, despite its lower quality. Gross N mineralization and consumption were also unaffected by differences in the ratio of fungal-to-bacterial growth. However, the ratio of C to gross N mineralization was lower than the average C/N of SOM, meaning that microorganisms specifically targeted N-rich components of OM, indicative of selective microbial N-mining. Consistent with the δ13C data, this reinforces evidence for the use of more microbially processed OM with a lower C/N ratio, rather than plant-derived OM. These results challenge the widely held assumption that microorganisms favor high-quality C sources and suggest that there is a trade-off in OM use that may be related to the growth-limiting factor for microorganisms in the ecosystem.
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| 49. |
- Hicks, Lettice C., et al.
(författare)
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The legacy of mixed planting and precipitation reduction treatments on soil microbial activity, biomass and community composition in a young tree plantation
- 2018
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Ingår i: Soil Biology and Biochemistry. - : Elsevier BV. - 0038-0717. ; 124, s. 227-235
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Tidskriftsartikel (refereegranskat)abstract
- Drought events are expected to increase as a consequence of climate change, with the potential to influence both plant and soil microbial communities. Mixed planting may be an option to mitigate drought stress to plants, however, the extent to which mixed planting mitigates the indirect effect of drought (reduced plant-derived carbon input) on soil microorganisms remains unknown. Using soils from a young experimental plantation in Central Europe, we investigated whether mixed planting (oak monoculture, and oak admixed with 1–3 other tree species) under simulated drought (50% precipitation reduction for 2 years) influenced soil microbial activity, biomass and community composition. To focus on legacy effects - i.e. indirect effects mediated by plant composition and a history of drought, rather than direct effects of reduced water availability - soils were measured at a standardised moisture content (28 ± 1% water holding capacity). Rates of bacterial growth and respiration were lower in soils with a legacy of drought. In contrast, fungal growth was not affected by a history of drought, suggesting that fungi were less adversely affected by reduced plant-input during drought, compared to bacteria. The effect of drought on the fungal-to-bacterial growth ratio was influenced by mixed planting, leading to a disproportionate decrease in bacterial growth in drought-exposed soils under oak monoculture than when oak was admixed with two or three different tree species. The presence of a particular tree species (with specific functional traits) in the admixture, rather than increased tree richness per se, may explain this response. Microbial biomass parameters, reflecting both the direct and indirect effects of past drought conditions, were consistently lower in drought-exposed soils than controls. While bacteria were more sensitive to the indirect effect of drought than fungi, the biomass concentrations suggested that the direct effect of reduced moisture affected both groups similarly. Overall, our findings demonstrate that drought can have lasting effects on microbial communities, with consequences for microbial function. Results also suggest that admixing oak with other tree species may alleviate the drought-legacy effect on bacteria and increase tolerance to future drought.
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| 50. |
- Hicks, Lettice C., et al.
(författare)
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Toward a function-first framework to make soil microbial ecology predictive
- 2022
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 103:e03594
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Tidskriftsartikel (refereegranskat)abstract
- Soil microbial communities perform vital ecosystem functions, such as the decomposition of organic matter to provide plant nutrition. However, despite the functional importance of soil microorganisms, attribution of ecosystem function to particular constituents of the microbial community has been impeded by a lack of information linking microbial function to community composition and structure. Here, we propose a function-first framework to predict how microbial communities influence ecosystem functions. We first view the microbial community associated with a specific function as a whole and describe the dependence of microbial functions on environmental factors (e.g., the intrinsic temperature dependence of bacterial growth rates). This step defines the aggregate functional response curve of the community. Second, the contribution of the whole community to ecosystem function can be predicted, by combining the functional response curve with current environmental conditions. Functional response curves can then be linked with taxonomic data in order to identify sets of “biomarker” taxa that signal how microbial communities regulate ecosystem functions. Ultimately, such indicator taxa may be used as a diagnostic tool, enabling predictions of ecosystem function from community composition. In this paper, we provide three examples to illustrate the proposed framework, whereby the dependence of bacterial growth on environmental factors, including temperature, pH, and salinity, is defined as the functional response curve used to interlink soil bacterial community structure and function. Applying this framework will make it possible to predict ecosystem functions directly from microbial community composition.
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