| 1. |
- 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
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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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| 2. |
- 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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| 3. |
- 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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| 4. |
- 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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| 5. |
- 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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| 6. |
- 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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| 7. |
- 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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| 8. |
- 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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| 10. |
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