| 1. |
- Rousk, Kathrin, et al.
(författare)
-
Feather moss nitrogen acquisition across natural fertility gradients in boreal forests
- 2013
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 61, s. 86-95
-
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.
|
|
| 2. |
- Rousk, Kathrin, et al.
(författare)
-
The Cyanobacterial Role in the Resistance of Feather Mosses to Decomposition-Toward a New Hypothesis
- 2013
-
Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 8:4
-
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.
|
|
| 3. |
- Ackermann, Kathrin, et al.
(författare)
-
N-2 Fixation in Feather Mosses is a Sensitive Indicator of N Deposition in Boreal Forests
- 2012
-
Ingår i: Ecosystems. - : Springer Science and Business Media LLC. - 1432-9840 .- 1435-0629. ; 15:6, s. 986-998
-
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.
|
|
| 4. |
- Bapiri, Azadeh, et al.
(författare)
-
Drying-Rewetting Cycles Affect Fungal and Bacterial Growth Differently in an Arable Soil
- 2010
-
Ingår i: Microbial Ecology. - : Springer Science and Business Media LLC. - 1432-184X .- 0095-3628. ; 60:2, s. 419-428
-
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.
|
|
| 5. |
- Barcenas-Moreno, Gema, et al.
(författare)
-
Fungal and bacterial recolonisation of acid and alkaline forest soils following artificial heat treatments
- 2011
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 43:5, s. 1023-1033
-
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.
|
|
| 6. |
- Bengtson, Per, et al.
(författare)
-
Archaeal abundance across a pH gradient in an arable soil and its relationship with bacterial and fungal growth rates.
- 2012
-
Ingår i: Applied and Environmental Microbiology. - 0099-2240. ; 78:16, s. 5906-5911
-
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.
|
|
| 7. |
- Birgander, Johanna, et al.
(författare)
-
Activity of temperate grassland plants and symbiotic fungi during the winter - implications for community structure and carbon cycling in a changing climate
- 2012
-
Ingår i: Nordic Journal of Botany. - : Wiley. - 0107-055X. ; 30:5, s. 513-521
-
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.
|
|
| 8. |
- Birgander, Johanna, et al.
(författare)
-
Comparison of fertility and seasonal effects on grassland microbial communities
- 2014
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 76, s. 80-89
-
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.
|
|
| 9. |
- Birgander, Johanna, et al.
(författare)
-
Temperature adaptation of bacterial growth and C-14-glucose mineralisation in a laboratory study
- 2013
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 65, s. 294-303
-
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.
|
|
| 10. |
- Fernandez-Lopez, David, et al.
(författare)
-
Bacterial pH-optima for growth track soil pH, but are higher than expected at low pH
- 2011
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 43:7, s. 1569-1575
-
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.
|
|
| 11. |
- Ford, H., et al.
(författare)
-
Grazing effects on microbial community composition, growth and nutrient cycling in salt marsh and sand dune grasslands
- 2013
-
Ingår i: Biology and Fertility of Soils. - : Springer Science and Business Media LLC. - 0178-2762 .- 1432-0789. ; 49:1, s. 89-98
-
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.
|
|
| 12. |
- Glanville, H., et al.
(författare)
-
Mineralization of low molecular weight carbon substrates in soil solution under laboratory and field conditions
- 2012
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 48, s. 88-95
-
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.
|
|
| 13. |
- Göransson, Hans, et al.
(författare)
-
Bacterial growth and respiration responses upon rewetting dry forest soils: Impact of drought-legacy
- 2013
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 57, s. 477-486
-
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.
|
|
| 14. |
- Haei, Mahsa, et al.
(författare)
-
Effects of soil frost on growth, composition and respiration of the soil microbial decomposer community
- 2011
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717 .- 1879-3428. ; 43:10, s. 2069-2077
-
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.
|
|
| 15. |
- Jones, D. L., et al.
(författare)
-
Biochar-mediated changes in soil quality and plant growth in a three year field trial
- 2012
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 45, s. 113-124
-
Tidskriftsartikel (refereegranskat)abstract
- While many laboratory studies have focused on the short term effects of biochar addition to soil), there have been comparatively few tracing its longer term effects in the field. This study investigated the multiyear impact of biochar on crop performance and soil quality with specific emphasis on carbon (C) and nitrogen (N) cycling over a 3 y period. Biochar was added to an agricultural field at 0, 25 and 50 t ha(-1) and planted with maize (year 1) and grass (years 2 and 3). Biochar addition affected plant performance in the grass crop with significant increases in foliar N (year 2) and above-ground biomass (year 3). Below-ground, biochar increased soil respiration, fungal and bacterial growth rate and turnover in year 2. This change coincided with a shift toward a bacterial dominated decomposer community, suggesting a decrease in the potential for microbially mediated C sequestration. Biochar did not affect dissolved organic C (DOC) and N (DON), NO3- or NH4+ pool sizes. Similarly, biochar addition had limited effects on the turnover of C-14-labelled SOC (plant litter), DOC (sugars and organic acids) and DON (amino acids) and no long term effect on N mineralization, NH3 volatilization, denitrification and NH4+ sorption. After 3 years in the field, the alkalinity associated with the biochar had been fully neutralized and biochar lost most of its cations (K, Na, Ca) but had built up an associated microbial community. We conclude that biochar addition to soil causes small and potentially transient changes in a temperate agroecosystem functioning. Importantly, many of the short-term effects of biochar on plant growth and soil behavior reported from laboratory studies were not observed in the field emphasizing the need for long term field trials to help inform agronomic management decisions involving biochar. (C) 2011 Elsevier Ltd. All rights reserved.
|
|
| 16. |
- Kamble, Pramod, et al.
(författare)
-
Bacterial growth and growth-limiting nutrients following chronic nitrogen additions to a hardwood forest soil
- 2013
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 59, s. 32-37
-
Tidskriftsartikel (refereegranskat)abstract
- Increasing nitrogen(N) deposition due to anthropogenic activities has become a significant global change threat to N-poor terrestrial ecosystems. We compared bacterial growth and nutrients limiting bacterial growth in one of the longest running experiments on increasing N-deposition to a temperate forest, the Chronic Nitrogen Amendment Study at Harvard Forest, USA. Soil samples were collected in fall 2009 from the organic and mineral horizons of plots treated annually since 1988 with 0 (unfertilized), 50(low N) or 150 (high N) kg N ha(-1) as NH4NO3. In the organic horizon, bacterial growth (leucine incorporation) decreased by 5 times in the high N plots compared to the unfertilized treatment, while no decrease was observed in the mineral horizon. Bacterial growth in all soils was primarily limited by lack of carbon (C), although adding only C (as glucose) resulted in only a minor increase in bacterial growth in the unfertilized soil compared to adding C in combination with N. The bacterial growth induced by adding only C increased with higher level of N fertilization, up to 7-8 times the level without any C addition in the high N treatment, suggesting increased availability of N for the bacteria with increasing N addition. (C) 2013 Elsevier Ltd. All rights reserved.
|
|
| 17. |
- Lopez-Sangil, Luis, et al.
(författare)
-
Microbial growth rate measurements reveal that land-use abandonment promotes a fungal dominance of SOM decomposition in grazed Mediterranean ecosystems
- 2011
-
Ingår i: Biology and Fertility of Soils. - : Springer Science and Business Media LLC. - 0178-2762 .- 1432-0789. ; 47:2, s. 129-138
-
Tidskriftsartikel (refereegranskat)abstract
- The present study investigated the effects of land-use abandonment on the soil decomposer community of two grazed Mediterranean ecosystems (an annual grassland with scattered holm oaks and a low-density shrubland). To test the influence of grazing abandonment, a set of plots within each site were fenced and kept undisturbed during 4-5 years, during which above-ground plant community structure was monitored. After that, soil samples were collected from grazed and abandoned plots corresponding to the three different soil conditions: away from ("grass") and below tree canopies ("oak") within the annual grassland, and from the shrubland ("shrub"). Soil samples were split into two different layers (0-5 and 5-15 cm) and then analyzed for saprotrophic fungal (acetate into ergosterol incorporation) and bacterial (leucine incorporation) growth rates. Ergosterol content (as a fungal biomass estimator) and a standard set of soil chemistry variables were also measured. After 5 years of grazing exclusion, saprotrophic fungal growth rate clearly increased in both grass and oak surface layers whereas bacterial growth rate was not altered. This translated into significantly higher fungal-to-bacterial (F/B) growth rate ratios within the ungrazed plots. Similar trends were observed for the shrub soils after 4 years of exclusion. On the contrary, abandonment of grazing had negligible effects on the ergosterol content, as well as on the soil chemical variables (soil organic carbon, total N, C/N ratio, and pH), in all the three soil conditions assessed. These results indicated a shift toward a more fungal-dominated decomposer activity in soils following cessation of grazing and highlighted the sensitivity of the microbial growth rate parameters to changes associated with land use. Moreover, there were evidences of a faster fungal biomass turnover in the ungrazed plots, which would reflect an accelerated, though not bigger, fungal channel in soil organic matter mineralization.
|
|
| 18. |
- Meisner, Annelein, et al.
(författare)
-
Microbial growth responses upon rewetting soil dried for four days or one year
- 2013
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 66, s. 188-192
-
Tidskriftsartikel (refereegranskat)abstract
- A pulse of respiration is induced by rewetting dry soil. Here we study the microbial responses underlying this pulse of respiration when rewetting soil dried for 4-days or 1-year. In the 4-days dried soil, respiration increased to a maximum rate immediately upon rewetting after which it decreased exponentially. In the 1-year dried soil, respiration also increased immediately, but then remained high for 16 h, after which it increased further, exponentially, with a peak rate after 20 h. The level of bacterial growth was initially lower in rewetted than in constantly moist soil, but started to increase linearly immediately upon rewetting 4-days dried soil. In 1-year dried soil, bacterial growth started only after a 16 h lag period of zero growth, and then increased exponentially to a peak after 30 h, at rates superseding those in continually moist soil. Fungal growth started to increase immediately upon rewetting, and reached the rate of the control soil after 2 days for the 4-days dried soil, and after a week for the 1-year dried soil. Thus, prolonged drying altered the pattern of bacterial and fungal growth after rewetting. Our results suggest that both fungal and bacterial growth are uncoupled from the initial respiration pulse and that growth responses and microbial C-use efficiency can be affected by prolonged drying. (C) 2013 Elsevier Ltd. All rights reserved.
|
|
| 19. |
- Quilliam, Richard S., et al.
(författare)
-
Nutrient dynamics, microbial growth and weed emergence in biochar amended soil are influenced by time since application and reapplication rate
- 2012
-
Ingår i: Agriculture, Ecosystems & Environment. - : Elsevier BV. - 1873-2305 .- 0167-8809. ; 158, s. 192-199
-
Tidskriftsartikel (refereegranskat)abstract
- Evidence suggests that in addition to sequestering carbon (C), biochar amendment can increase crop yields, improve soil quality and nutrient cycling, reduce the leaching of nutrients from soil and stimulate soil microbial activity. However, biochar application primarily benefits soils of intrinsic poor quality, thus the advantages of adding biochar to temperate agricultural soils remains controversial. In addition, there is limited information about the longer term effects of biochar application, or of increasing the rate of biochar loading to soil. Therefore, the aim of this study was to determine the effect of biochar residency time and application rate on soil quality, crop performance, weed emergence, microbial growth and community composition in a temperate agricultural soil. We used replicated field plots with three wood biochar application rates (0, 25 and 50 t ha(-1)). Three years after biochar amendment, the plots were further split and fresh biochar added at two different rates (25 and 50 t ha(-1)) resulting in double-loaded reapplications of 25 + 25 and 50 + 50 t ha(-1). After a soil residency time of three years, there were no significant differences in soil nutrients, microbial growth, mycorrhizal colonisation or weed emergence between biochar amended and unamended soil. In contrast, the reapplication of biochar had a significant effect on soil quality, (e.g. increased PO43-, K+ and Ca2+, DOC, soil moisture, organic matter and EC), microbial growth, (e.g. decreased saprophytic fungal growth), increased mycorrhizal root colonisation and inhibition of weed emergence. Whilst biochar application is unquestionably a strategy for the sequestration of C, in this case, other benefits, e.g. improved soil nutrient levels or crop performance, seemed to be short lived. Reapplication of biochar exemplifies the transient nature of biochar-mediated benefits rather than any lasting differences in soil nutrient dynamics or microbial communities. These results emphasise the need for more long-term field studies to provide data that can meaningfully inform agronomic management decisions and climate change mitigation strategies. (C) 2012 Elsevier B.V. All rights reserved.
|
|
| 20. |
- Reischke, Stephanie, et al.
(författare)
-
The effects of glucose loading rates on bacterial and fungal growth in soil
- 2014
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 70, s. 88-95
-
Tidskriftsartikel (refereegranskat)abstract
- Microbial activity in soil is usually limited by the availability of carbon (C). Adding an easily available C source, like glucose, has therefore been a common approach to study alleviation of resource limitations. Most such studies have relied on respiration to study microbial dynamics, with few following the explicit growth response. We determined the response in bacterial and fungal growth, as well as respiration, to additions of glucose (0.5-32 mg C g(-1) soil) during up to 6 days, using leucine incorporation for bacterial growth and acetate-in-ergosterol incorporation for fungal growth. A concentration of 2 mg glucose-C g(-1) soil, where the fungal contribution appeared to be small, was also studied with a high time resolution. Adding glucose resulted in an initial lag phase of stable respiration and bacterial growth. Bacterial growth was similar to the unamended control, while respiration was 8 fold higher during this period. The 14-h lag phase was followed by an exponential increase for both respiration and bacterial growth, with a similar intrinsic growth rate (mu) of around 0.25 h(-1). After the exponential phase, bacterial growth decreased exponentially. The respiration initially decreased even more rapidly than bacterial growth. At concentrations exceeding 4 mg glucose-C g(-1) the relative stimulation of fungal growth surpassed that of bacteria, with the highest amendment rates, 32 mg C g(-1), resulting in mainly fungal growth. Lower loading rates than 4 mg glucose-C g(-1) appeared to stimulate mainly bacterial growth. (C) 2013 Elsevier Ltd. All rights reserved.
|
|
| 21. |
- Rousk, Johannes, et al.
(författare)
-
Bacterial salt tolerance is unrelated to soil salinity across an arid agroecosystem salinity gradient
- 2011
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 43:9, s. 1881-1887
-
Tidskriftsartikel (refereegranskat)abstract
- In arid and semi-arid ecosystems, salinization is a major threat to the productivity of agricultural land. While the influence of other physical and chemical environmental factors on decomposer microorganisms have been intensively studied in soil, the influence of salinity has been less exhaustively assessed. We investigated the influence of soil salinity on soil bacterial communities in soils covering a range of salt levels. We assessed tolerance of the bacterial communities from Libyan agricultural soils forming a salinity gradient to salt (NaCl), by extracting bacterial communities and instantaneously monitoring the concentration–response to added NaCl with the Leucine incorporation technique for bacterial growth. To maximise our ability to detect differences in bacterial salt tolerance between the soils, we also repeated the assessment of bacterial growth tolerance after one month incubation with 1 or 2% added organic matter additions to stimulate microbial growth levels. We could establish clear concentration–response relationships between bacterial growth and soil salinity, demonstrating an accurate assessment of bacterial tolerance. The in situ soil salinity in the studied soils ranged between 0.64 and 2.73 mM Na (electrical conductivities of 0.74–4.12 mS cm−1; cation exchange capacities of 20–37 mmolc kg−1) and the bacterial tolerance indicated by the concentration inhibiting 50% of the bacterial growth (EC50) varied between 30 and 100 mM Na or between electrical conductivities of 3.0 and 10.7 mS cm−1. There was no relationship between in situ soil salinity and the salt tolerance of the soil bacterial communities. Our results suggest that soil salinity was not a decisive factor for bacterial growth, and thus for structuring the decomposer community, in the studied soils.
|
|
| 22. |
- Rousk, Johannes, et al.
(författare)
-
Comparative Toxicity of Nanoparticulate CuO and ZnO to Soil Bacterial Communities
- 2012
-
Ingår i: PLoS ONE. - : Public Library of Science (PLoS). - 1932-6203. ; 7:3
-
Tidskriftsartikel (refereegranskat)abstract
- The increasing industrial application of metal oxide Engineered Nano-Particles (ENPs) is likely to increase their environmental release to soils. While the potential of metal oxide ENPs as environmental toxicants has been shown, lack of suitable control treatments have compromised the power of many previous assessments. We evaluated the ecotoxicity of ENP (nano) forms of Zn and Cu oxides in two different soils by measuring their ability to inhibit bacterial growth. We could show a direct acute toxicity of nano-CuO acting on soil bacteria while the macroparticulate (bulk) form of CuO was not toxic. In comparison, CuSO4 was more toxic than either oxide form. Unlike Cu, all forms of Zn were toxic to soil bacteria, and the bulk-ZnO was more toxic than the nano-ZnO. The ZnSO4 addition was not consistently more toxic than the oxide forms. Consistently, we found a tight link between the dissolved concentration of metal in solution and the inhibition of bacterial growth. The inconsistent toxicological response between soils could be explained by different resulting concentrations of metals in soil solution. Our findings suggested that the principal mechanism of toxicity was dissolution of metal oxides and sulphates into a metal ion form known to be highly toxic to bacteria, and not a direct effect of nano-sized particles acting on bacteria. We propose that integrated efforts toward directly assessing bioavailable metal concentrations are more valuable than spending resources to reassess ecotoxicology of ENPs separately from general metal toxicity.
|
|
| 23. |
- Rousk, Johannes, et al.
(författare)
-
Fungal and bacterial growth responses to N fertilization and pH in the 150-year 'Park Grass' UK grassland experiment.
- 2011
-
Ingår i: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 76, s. 89-99
-
Tidskriftsartikel (refereegranskat)abstract
- The effects of nitrogen (N) fertilization (0-150 kg N ha(-1) year(-1) since 1865) and pH (3.3-7.4) on fungal and bacterial growth, biomass and phospholipid fatty acid (PLFA) composition were investigated in grassland soils from the 'Park Grass Experiment', Rothamsted Research, UK. Bacterial growth decreased and fungal growth increased with lower pH, resulting in a 50-fold increase in the relative importance of fungi between pH 7.4 and 3.3. The PLFA-based fungal : bacterial biomass ratio was unchanged between pH 4.5 and 7.4, and decreased only below pH 4.5. Respiration and substrate-induced respiration biomass both decreased three- to fourfold with lower pH, but biomass concentrations estimated using PLFAs were unaffected by pH. N fertilization did not affect bacterial growth and marginally affected fungal growth while PLFA biomass marker concentrations were all reduced by higher N additions. Respiration decreased with higher N application, suggesting a reduced quality of the soil organic carbon. The PLFA composition was strongly affected by both pH and N. A comparison with a pH gradient in arable soil allowed us to generalize the pH effect between systems. There are 30-50-fold increases in the relative importance of fungi between high (7.4-8.3) and low (3.3-4.5) pH with concomitant reductions of respiration by 30-70%.
|
|
| 24. |
- Rousk, Johannes, et al.
(författare)
-
Growth of saprotrophic fungi and bacteria in soil.
- 2011
-
Ingår i: FEMS Microbiology Ecology. - : Oxford University Press (OUP). - 1574-6941 .- 0168-6496. ; 78, s. 17-30
-
Tidskriftsartikel (refereegranskat)abstract
- Bacterial and fungal growth rate measurements are sensitive variables to detect changes in environmental conditions. However, while methods to assess the species composition and biomass of fungi and bacteria has made much progress, information about growth rates remains surprisingly rudimentary. We review the recent history of approaches to assess bacterial and fungal growth rates, leading up to current methods, especially focusing on leucine/thymidine incorporation to estimate bacterial growth and acetate incorporation into ergosterol to estimate fungal growth. We present underlying assumptions for these methods, compare estimates of turnover times for fungi and bacteria based on them, and discuss issues, including e.g. elusive conversion factors. We review what the application of fungal and bacterial growth rate methods has revealed regarding the influence of the environmental factors of temperature, moisture (including drying/rewetting), pH, as well as the influence of substrate additions, presence of plants and toxins. We highlight experiments exploring competitive and facilitative interaction between bacteria and fungi enabled using growth rate methods. Finally, we predict that growth methods will be an important complement to molecular approaches to elucidate fungal and bacterial ecology, and we identify methodological concerns and how they should be addressed.
|
|
| 25. |
- Rousk, Johannes, et al.
(författare)
-
Investigating the long-term legacy of drought and warming on the soil microbial community across five European shrubland ecosystems.
- 2013
-
Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 19:12, s. 3872-3884
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated how the legacy of warming and summer-drought affected microbial communities in five different replicated long-term (>10 years) field-experiments across Europe (EU-FP7 INCREASE infrastructure). To focus explicitly on legacy effects (i.e. indirect rather than direct effects of the environmental factors), we measured microbial variables under the same moisture and temperature in a brief screening, and following a pre-incubation at stable conditions. Specifically, we investigated the size and composition of the soil microbial community (PLFA) alongside measurements of bacterial (leucine incorporation) and fungal (acetate in ergosterol incorporation) growth rates, previously shown to be highly responsive to changes in environmental factors, and microbial respiration. We found no legacy effects on the microbial community size, composition, growth rates or basal respiration rates at the effect sizes used in our experimental setup (0.6°C, about 30% precipitation reduction). Our findings support previous reports from single short-term ecosystem studies thereby providing a clear evidence base to allow long term, broad scale generalizations to be made. The implication of our study is that warming and summer drought will not result in legacy effects on the microbial community and their processes within the effect sizes here studied. While legacy effects on microbial processes during perturbation cycles, such as drying-rewetting, and on tolerance to drought and warming remains to be studied, our results suggest that any effects on overall ecosystem processes will be rather limited. Thus, the legacies of warming and drought should not be prioritised factors to consider when modelling contemporary rates of biogeochemical processes in soil. This article is protected by copyright. All rights reserved.
|
|
| 26. |
- Rousk, Johannes, et al.
(författare)
-
Investigating the mechanisms for the opposing pH relationships of fungal and bacterial growth in soil
- 2010
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 42:6, s. 926-934
-
Tidskriftsartikel (refereegranskat)abstract
- Soil pH is one of the most influential variables in soil, and is a powerful factor in influencing the size, activity and community structure of the soil microbial community. It was previously shown in a century old artificial pH gradient in an arable soil (pH 4.0-8.3) that bacterial growth is positively related to pH, while fungal growth increases with decreasing pH. In an attempt to elucidate some of the mechanisms for this, plant material that especially promotes fungal growth (straw) or bacterial growth (alfalfa) was added to soil samples of the pH gradient in 5-day laboratory incubation experiments. Also, bacterial growth was specifically inhibited by applying a selective bacterial growth inhibitor (bronopol) along the entire pH gradient to investigate if competitive interaction caused the shift in the decomposer community along the gradient. Straw benefited fungal growth relatively more than bacterial, and vice versa for alfalfa. The general pattern of a shift in fungal:bacterial growth with pH was, however, unaffected by substrate additions, indicating that lack of a suitable substrate was not the cause of the pH effect on the microbial community. In response to the bacterial growth inhibition by bronopol, there was stimulation of fungal growth up to pH 7, but not beyond, both for alfalfa and straw addition. However, the accumulation of ergosterol (an indicator of fungal biomass) during the incubation period after adding alfalfa increased at all pHs, indicating that fungal growth had been high at some time during the 5-day incubation following joint addition of alfalfa and bronopol. This was corroborated in a time-series experiment. In conclusion, the low fungal growth at high pH in an arable soil was caused to a large extent by bacterial competition, and not substrate limitation. (C) 2010 Elsevier Ltd. All rights reserved.
|
|
| 27. |
|
|
| 28. |
- Rousk, Johannes, et al.
(författare)
-
Loss of low molecular weight dissolved organic carbon (DOC) and nitrogen (DON) in H2O and 0.5 M K2SO4 soil extracts
- 2010
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 42:12, s. 2331-2335
-
Tidskriftsartikel (refereegranskat)abstract
- Soil extracts are routinely used to quantify dissolved organic nutrient concentrations in soil. Here we studied the loss and transformation of low molecular weight (LMW) components of DOC (C-14-glucose, 1 and 100 mu M) and DON (C-14-amino acid mixture, 1 and 100 mu M) during extraction of soil (0-6 h) with either distilled water or 0.5 M K2SO4. The extractions were performed at 20 degrees C, at 4 degrees C, or in the presence of an inhibitor of microbial activity (HgCl2 and Na-azide). We showed that both glucose and amino acids became progressively lost from solution with increasing shaking time. The greatest loss was observed in H2O extracts at 1 mu M for both substances (>90% loss after 15 min). Lower temperature (4 degrees C) and presence of K2SO4 both resulted in reduced loss rates. The presence of microbial inhibitors effectively eliminated the loss of glucose and amino acids. We conclude that microbial transformation of LMW-DOC and DON during H2O or K2SO4 extraction of soil may affect the estimation of their concentrations in soil. This finding has significant implications for methods that rely on chemical extractions to estimate LMW-C components of DOC and DON. (c) 2010 Elsevier Ltd. All rights reserved.
|
|
| 29. |
|
|
| 30. |
- Rousk, Johannes, et al.
(författare)
-
Soil bacterial and fungal communities across a pH gradient in an arable soil.
- 2010
-
Ingår i: The Isme Journal. - : Springer Science and Business Media LLC. - 1751-7362 .- 1751-7370. ; 4, s. 1340-1351
-
Tidskriftsartikel (refereegranskat)abstract
- Soils collected across a long-term liming experiment (pH 4.0-8.3), in which variation in factors other than pH have been minimized, were used to investigate the direct influence of pH on the abundance and composition of the two major soil microbial taxa, fungi and bacteria. We hypothesized that bacterial communities would be more strongly influenced by pH than fungal communities. To determine the relative abundance of bacteria and fungi, we used quantitative PCR (qPCR), and to analyze the composition and diversity of the bacterial and fungal communities, we used a bar-coded pyrosequencing technique. Both the relative abundance and diversity of bacteria were positively related to pH, the latter nearly doubling between pH 4 and 8. In contrast, the relative abundance of fungi was unaffected by pH and fungal diversity was only weakly related with pH. The composition of the bacterial communities was closely defined by soil pH; there was as much variability in bacterial community composition across the 180-m distance of this liming experiment as across soils collected from a wide range of biomes in North and South America, emphasizing the dominance of pH in structuring bacterial communities. The apparent direct influence of pH on bacterial community composition is probably due to the narrow pH ranges for optimal growth of bacteria. Fungal community composition was less strongly affected by pH, which is consistent with pure culture studies, demonstrating that fungi generally exhibit wider pH ranges for optimal growth.
|
|
| 31. |
- Rousk, Johannes, et al.
(författare)
-
Temperature adaptation of bacterial communities in experimentally warmed forest soils
- 2012
-
Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 18:10, s. 3252-3258
-
Tidskriftsartikel (refereegranskat)abstract
- A detailed understanding of the influence of temperature on soil microbial activity is critical to predict future atmospheric CO2 concentrations and feedbacks to anthropogenic warming. We investigated soils exposed to 3-4 years of continuous 5 degrees C-warming in a field experiment in a temperate forest. We found that an index for the temperature adaptation of the microbial community, T-min for bacterial growth, increased by 0.19 degrees C per 1 degrees C rise in temperature, showing a community shift towards one adapted to higher temperature with a higher temperature sensitivity (Q(10(5-15 degrees C)) increased by 0.08 units per 1 degrees C). Using continuously measured temperature data from the field experiment we modelled in situ bacterial growth. Assuming that warming did not affect resource availability, bacterial growth was modelled to become 60% higher in warmed compared to the control plots, with the effect of temperature adaptation of the community only having a small effect on overall bacterial growth (<5%). However, 3 years of warming decreased bacterial growth, most likely due to substrate depletion because of the initially higher growth in warmed plots. When this was factored in, the result was similar rates of modelled in situ bacterial growth in warmed and control plots after 3 years, despite the temperature difference. We conclude that although temperature adaptation for bacterial growth to higher temperatures was detectable, its influence on annual bacterial growth was minor, and overshadowed by the direct temperature effect on growth rates.
|
|
| 32. |
- Rousk, Johannes, et al.
(författare)
-
The microbial PLFA composition as affected by pH in an arable soil
- 2010
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 42:3, s. 516-520
-
Tidskriftsartikel (refereegranskat)abstract
- The influence of soil pH on the phospholipid fatty acid (PLFA) composition of the microbial community was investigated along the Hoosfield acid strip, Rothamsted Research, UK - a uniform pH gradient between pH 8.3 and 4.5. The influence of soil pH on the total concentration of PLFAs was not significant, while biomass estimated using substrate induced respiration decreased by about 25%. However, the PLFA composition clearly changed along the soil pH gradient. About 40% of the variation in PLFA composition along the gradient was explained by a first principal component, and the sample scores were highly correlated to pH (R-2 = 0.97). Many PLFAs responded to pH similarly in the Hoosfield arable soil compared with previous assessments in forest soils, including, e.g. monounsaturated PLFAs 16:1 omega 5, 16:1 omega 7c and 18:1 omega 7, which increased in relative concentrations with pH, and i16:0 and cy19:0, both of which decreased with pH. Some PLFAs responded differently to pH between the soil types, e.g. br18:0. We conclude that soil pH has a profound influence on the microbial PLFA composition, which must be considered in all applications of this method to detect changes in the microbial community. (C) 2009 Elsevier Ltd. All rights reserved.
|
|
| 33. |
- Rousk, Johannes, et al.
(författare)
-
Transient biochar effects on decomposer microbial growth rates: evidence from two agricultural case-studies
- 2013
-
Ingår i: European Journal of Soil Science. - : Wiley. - 1365-2389 .- 1351-0754. ; 64:6, s. 770-776
-
Tidskriftsartikel (refereegranskat)abstract
- We investigated the impact of biochar application on fungal (acetate incorporation into ergosterol) and bacterial (leucine incorporation) growth rates in two case studies: a temperate UK pasture soil and a Mediterranean Australian agricultural soil. We added biochar at similar rates per unit of soil organic carbon (SOC) and monitored both the immediate (after 1week equilibration) and longer-term (1-3years) effects. The immediate effect of the biochar applied to the UK soil was a decreased fungal-to-bacterial growth ratio, driven by greater bacterial growth. The immediate effect of biochar application to the Australian soils was subtle, only slightly increasing the fungal-to-bacterial growth ratio. In both case studies, the biochar effects were transient, and no long-term effects (1-3years) on microbial growth rates could be detected in either soil. The bacterial growth increase in the UK soil was probably related to a release of large amounts of labile C from the biochar, or as C released from the resident SOM caused by the biochar-induced pH increase. The increase in fungal-to-bacterial growth ratio could be related to a release of poor quality C in the Australian soils. There were immediate effects of biochar application on microbial growth in agricultural soils, but they were disparate between cases, making any generalization of mechanisms difficult. However, the microbial responses were consistently transient. Taken together, biochar application to agricultural soil appears to have an impact upon the decomposer community, suggesting limited resistance. However, the microbial functioning appeared resilient to these effects, stabilizing microbial communities to their initial state within 1-3years of application.
|
|
| 34. |
- Rousk, Johannes, et al.
(författare)
-
Using the concentration-dependence of respiration arising from glucose addition to estimate in situ concentrations of labile carbon in grassland soil
- 2014
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 77, s. 81-88
-
Tidskriftsartikel (refereegranskat)abstract
- In this study, we first determined the low molecular weight dissolved organic carbon (LMW DOC) concentration-dependent kinetics of soil respiration in a temperate grassland soil sampled on successive occasions. We then used the established relationship to estimate in situ LMW DOC concentrations from basal respiration measurements. C-14-labelled glucose was used as a model substrate and was added to soil over a wide range of concentrations (0.05-4000 mu g C g(-1) DW soil; equivalent to ca. 2.5 mu M-200 mM glucose-C). The time-dependent loss of C-14-glucose to (CO2)-C-14 was similar to previous assessments. The Michaelis-Menten parameter V-max varied between 17 (September 2010) and 42 (October 2010) mu g CO2-C g(-1) h(-1) (corresponding to 1.4-3.5 mu mol CO2 g(-1) h(-1)), while K-m varied between 893 (September 2010) and 1990 (October 2010) mu g glucose-C g(-1) (41-92 mM glucose), thus within the span previously reported for soils, albeit in the higher end of the range. However, the estimates were 6 orders-of-magnitude greater than those found in previous studies in natural waters. A possible methodological reason for this difference was an induced multiphasic concentration dependence, biasing K-m and V-max with high concentrations of LMW DOC. By combining the established concentration dependences with measurements of basal respiration, we estimated in situ concentrations of LMW DOC of 131 (October 2010), 112 January 2011) and 270 (September 2010) mu g LMW DOC g(-1), far exceeding the total DOC concentration in the soil (17-20 mu g DOC g(-1) soil), thus invalidating our approach. We propose a way forward, and suggest that although current estimates of LMW DOC cycling need revision, there is evidence for a rapidly cycling pool of LMW DOC, possibly turning over >30 times per day, that warrants further attention. (C) 2014 Elsevier Ltd. All rights reserved.
|
|
| 35. |
- Strickland, Michael S., et al.
(författare)
-
Considering fungal:bacterial dominance in soils - Methods, controls, and ecosystem implications
- 2010
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 42:9, s. 1385-1395
-
Forskningsöversikt (refereegranskat)abstract
- An expectation in soil ecology is that a microbial communities' fungal:bacterial dominance indicates both its response to environmental change and its impact on ecosystem function. We review a selection of the increasing body of literature on this subject and assess the relevance of its expectations by examining the methods used to determine, the impact of environmental factors on, and the expected ecosystem consequences of fungal:bacterial dominance. Considering methods, we observe that fungal:bacterial dominance is contingent on the actual measure used to estimate it. This has not been carefully considered; fungal:bacterial dominance of growth, biomass, and residue indicate different, and not directly relatable aspects, of the microbial community's influence on soil functioning. Considering relationships to environmental factors, we found that shifts in fungal:bacterial dominance were not always in line with the general expectation, in many instances even being opposite to them. This is likely because the traits expected to differentiate bacteria from fungi are often not distinct. Considering the impact of fungal:bacterial dominance on ecosystem function, we similarly found that expectations were not always upheld and this too could be due to trait overlap between these two groups. We explore many of the potential reasons why expectations related to fungal:bacterial dominance were not met, highlighting areas where future research, especially furthering a basic understanding of the ecology of bacteria and fungi, is needed. (C) 2010 Elsevier Ltd. All rights reserved.
|
|
| 36. |
- van Groenigen, Kees-Jan, et al.
(författare)
-
Abundance, production and stabilization of microbial biomass under conventional and reduced tillage
- 2010
-
Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 42:1, s. 48-55
-
Tidskriftsartikel (refereegranskat)abstract
- Soil tillage practices affect the soil microbial community in various ways, with possible consequences for nitrogen (N) losses, plant growth and soil organic carbon (C) sequestration. As microbes affect soil organic matter (SOM) dynamics largely through their activity, their impact may not be deduced from biomass measurements alone. Moreover, residual microbial tissue is thought to facilitate SOM stabilization, and to provide a long term integrated measure of effects on the microorganisms. In this study, we therefore compared the effect of reduced (RT) and conventional tillage (CT) on the biomass, growth rate. and residues of the major microbial decomposer groups fungi and bacteria. Soil samples were collected at two depths (0-5 cm and 5-20 cm) from plots in an Irish winter wheat field that were exposed to either conventional or shallow non-inversion tillage for 7 growing seasons. Total soil fungal and bacterial biomasses were estimated using epifluorescence microscopy. To separate between biomass of saprophytic fungi and arbuscular mycorrhizae, samples were analyzed for ergosterol and phospholipid fatty acid (PLFA) biomarkers. Growth rates of saprophytic fungi were determined by [C-14]acetate-in-ergosterol incorporation, whereas bacterial growth rates were determined by the incorporation of H-3-leucine in bacterial proteins. Finally, soil contents of fungal and bacterial residues were estimated by quantifying microbial derived amino sugars. Reduced tillage increased the total biomass of both bacteria and fungi in the 0-5 cm soil layer to a similar extent. Both ergosterol and PLFA analyses indicated that RT increased biomass of saprophytic fungi in the 0-5 cm soil layer. In contrast, RT increased the biomass of arbuscular mycorrhizae as well as its contribution to the total fungal biomass across the whole plough layer. Growth rates of both saprotrophic fungi and bacteria on the other hand were not affected by soil tillage, possibly indicating a decreased turnover rate of soil microbial biomass under RT. Moreover, RT did not affect the proportion of microbial residues that were derived from fungi. In summary, our results suggest that RT can promote soil C storage without increasing the role of saprophytic fungi in SOM dynamics relative to that of bacteria. (C) 2009 Elsevier Ltd. All rights reserved.
|
|
| 37. |
- Walsh, John J., et al.
(författare)
-
Fungal and bacterial growth following the application of slurry and anaerobic digestate of livestock manure to temperate pasture soils
- 2012
-
Ingår i: Biology and Fertility of Soils. - : Springer Science and Business Media LLC. - 0178-2762 .- 1432-0789. ; 48:8, s. 889-897
-
Tidskriftsartikel (refereegranskat)abstract
- How land-application of digestate sourced from anaerobic digestion (AD) of animal waste influences the functioning of a mixed pasture agroecosystem is not well characterised, particularly with regard to the response of the actively growing microbial community. We studied the impact of the liquid AD digestate on the decomposer community in two different soils, seeded with two different common grassland crops; a mixture of either grass or grass/clover in a greenhouse experiment. We studied bacterial (leucine incorporation into bacteria) and fungal (acetate incorporation into ergosterol) growth responses to AD cattle slurry digestate, undigested cattle slurry, mineral fertiliser (NPK and N) added at a rate equivalent to 150 kg N ha(-1), and a no-fertiliser control treatment. Differences in fungal and bacterial growth were evident between the soil and sward types. However, the fertilisers consistently stimulated a higher bacterial growth than the no-fertiliser control, and liquid digestate resulted in a level of bacterial growth higher or equal to that of mineral fertiliser, whilst undigested slurry resulted in lower bacterial growth. These fertiliser effects on bacterial growth mirrored the effects on plant growth. In contrast, the fungal community responded only marginally to fertiliser treatments. We conclude that the application of digestate stimulates the bacterial decomposer community in a similar way to that of mineral fertilisers. Our results suggest that mineral fertiliser can be exchanged for liquid digestate with limited impact on the actively growing soil microbial community that, in turn, regulate important soil processes including nutrient cycling in agricultural soils.
|
|
