Nitrous oxide (N2O) emissions are closely linked to agricultural fertilisation. European and national policy incentives have been set to reduce greenhouse gas (GHG) emissions; however, only a few ...evaluations have been conducted. Avoiding such emissions is an important climate change mitigation measure, but it is still uncertain which management measures over a long‐term, best out‐balance crop yield and GHG balances in agricultural systems. We here used the process‐based LandscapeDNDC model to simulate N2O emissions and trade‐offs in yield and soil nitrogen budget for four alternative arable cropping systems in three Austrian agricultural production zones belonging to different climatic regions. We evaluated statistical data on crop rotations and management practices, predominant soil types, and 10‐year daily weather conditions for four cropping systems: (1) conventional farming receiving the maximum allowed nitrogen fertilisation rate (Nmax), (2) conventional farming receiving 15% less fertiliser, (3) conventional farming receiving 25% less fertiliser, and (4) organic farming. Our results showed that soil N2O emissions could be best reduced in wet, high‐yield regions. Reducing nitrogen fertilisation by 15% and 25% mitigated N2O emissions by, on average, 22% and 39%, respectively, while the yield was reduced by 5% and 9%, respectively. In comparison, the same crops grown in the organic cropping system released 60% less N2O, but yield declined on average by 23%. Corn, winter barley, and vegetables showed the highest N2O reduction potential under reduced fertiliser input in conventional farming. In addition to N2O emissions, reduced fertilisation substantially decreased other nitrogen losses into the water and atmosphere. Generally, the soils under all cropping systems maintained a positive mean nitrogen budget. Our results suggest a significant emission reduction potential in certain production zones which, however, were accompanied by yield reductions. Knowledge of the emission patterns from cropping systems under different environmental conditions is essential to set the appropriate measures. In addition, region‐specific measures to reduce soil N2O emissions have to be in line with farmers' interests in order to facilitate the successful implementation of targeted nitrogen management.
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Global warming has the potential to increase soil respiration (RS), one of the major fluxes in the global carbon (C) cycle. RS consists of an autotrophic (RA) and a heterotrophic (RH) component. We ...combined a soil warming experiment with a trenching experiment to assess how RS, RA, and RH are affected. The experiment was conducted in a mature forest dominated by Norway spruce. The site is located in the Austrian Alps on dolomitic bedrock. We warmed the soil of undisturbed and trenched plots by means of heating cables 4 °C above ambient during the snow-free seasons of 2005 and 2006. Soil warming increased the CO₂ efflux from control plots (RS) by ~45% during 2005 and ~47% during 2006. The CO₂ efflux from trenched plots (RH) increased by ~39% during 2005 and ~45% during 2006. Similar responses of RS and RH indicated that the autotrophic and heterotrophic components of RS responded equally to the temperature increase. Thirty-five to forty percent or 1 t C ha⁻¹ yr⁻¹ of the overall annual increase in RS (2.8 t C ha⁻¹ yr⁻¹) was autotrophic. The remaining, heterotrophic part of soil respiration (1.8 t C ha⁻¹ yr⁻¹), represented the warming-induced C loss from the soil. The autotrophic component showed a distinct seasonal pattern. Contribution of RA to RS was highest during summer. Seasonally derived Q₁₀ values reflected this pattern and were correspondingly high (5.3-9.3). The autotrophic CO₂ efflux increase due to the 4 °C warming implied a Q₁₀ of 2.9. Hence, seasonally derived Q₁₀ of RA did not solely reflect the seasonal soil temperature development.
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Cover crops (CC) offer numerous benefits to agroecosystems, particularly in the realm of soil organic carbon (SOC) accrual and loss mitigation. However, uncertainties persist regarding the extent to ...which CCs, in co‐occurrence with environmental factors, influence SOC responses and associated C pools. We therefore performed a weighted meta‐analysis on the effects of CCs on the mineral‐associated organic carbon (MAOC), the particulate organic carbon (POC) and the microbial biomass carbon (MBC) pool compared to no CC cultivation in arable cropland. Our study summarized global research of comparable management, with a focus on climatic zones representative of Europe, such as arid, temperate and boreal climates. In this meta‐analysis, we included 71 independent studies from 61 articles published between 1990 and June 2023 in several scientific and grey literature databases. Sensitivity analysis was conducted and did not identify any significant publication bias. The results revealed that CCs had an overall statistically significant positive effect on SOC pools, increasing MAOC by 4.8% (95% CI: 0.6%–9.4%, n = 16), POC by 23.2% (95% CI: 13.9%–34.4%, n = 39) and MBC by 20.2% (95% CI: 11.7%–30.7%, n = 30) in the top soil, compared to no CC cultivation. Thereby, CCs feed into the stable as well as the more labile C pools. The effect of CCs on MAOC was dependent on soil clay content and initial SOC concentration, whereas POC was influenced by moderators such as CC peak biomass and experiment duration. For MBC, for example, clay content, crop rotation duration and tillage depth were identified as important drivers. Based on our results on the effects of CCs on SOC pools and significant moderators, we identified several research needs. A pressing need for additional experiments exploring the effects of CCs on SOC pools was found, with a particular focus on MAOC and POC. Further, we emphasize the necessity for conducting European studies spanning the north–south gradient. In conclusion, our results show that CC cultivation is a key strategy to promote C accrual in different SOC pools. Additionally, this meta‐analysis provides new insights into the state of knowledge regarding SOC pool changes influenced by CCs, offering quantitative summary results and shedding light on the sources of heterogeneity affecting these findings.
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Climate change may considerably impact the carbon (C) dynamics and C stocks of forest soils. To assess the combined effects of warming and reduced precipitation on soil CO2 efflux, we conducted a ...two‐way factorial manipulation experiment (4 °C soil warming + throughfall exclusion) in a temperate spruce forest from 2008 until 2010. Soil was warmed by heating cables throughout the growing seasons. Soil drought was simulated by throughfall exclusions with three 100 m2 roofs during 25 days in July/August 2008 and 2009. Soil warming permanently increased the CO2 efflux from soil, whereas throughfall exclusion led to a sharp decrease in soil CO2 efflux (45% and 50% reduction during roof installation in 2008 and 2009, respectively). In 2008, CO2 efflux did not recover after natural rewetting and remained lowered until autumn. In 2009, CO2 efflux recovered shortly after rewetting, but relapsed again for several weeks. Drought offset the increase in soil CO2 efflux by warming in 2008 (growing season CO2 efflux in t C ha−1: control: 7.1 ± 1.0; warmed: 9.5 ± 1.7; warmed + roof: 7.4 ± 0.3; roof: 5.9 ± 0.4) and in 2009 (control: 7.6 ± 0.8; warmed + roof: 8.3 ± 1.0). Throughfall exclusion mainly affected the organic layer and the top 5 cm of the mineral soil. Radiocarbon data suggest that heterotrophic and autotrophic respiration were affected to the same extent by soil warming and drying. Microbial biomass in the mineral soil (0–5 cm) was not affected by the treatments. Our results suggest that warming causes significant C losses from the soil as long as precipitation patterns remain steady at our site. If summer droughts become more severe in the future, warming induced C losses will likely be offset by reduced soil CO2 efflux during and after summer drought.
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Plant seasonal cycles alter carbon (C) and nitrogen (N) availability for soil microbes, which may affect microbial community composition and thus feed back on microbial decomposition of soil organic ...material and plant N availability. The temporal dynamics of these plant-soil interactions are, however, unclear. Here, we experimentally manipulated the C and N availability in a beech forest through N fertilization or tree girdling and conducted a detailed analysis of the seasonal pattern of microbial community composition and decomposition processes over 2 yr. We found a strong relationship between microbial community composition and enzyme activities over the seasonal course. Phenoloxidase and peroxidase activities were highest during late summer, whereas cellulase and protease peaked in late autumn. Girdling, and thus loss of mycorrhiza, resulted in an increase in soil organic matter-degrading enzymes and a decrease in cellulase and protease activity. Temporal changes in enzyme activities suggest a switch of the main substrate for decomposition between summer (soil organic matter) and autumn (plant litter). Our results indicate that ectomycorrhizal fungi are possibly involved in autumn cellulase and protease activity. Our study shows that, through belowground C allocation, trees significantly alter soil microbial communities, which may affect seasonal patterns of decomposition processes.
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Abstract
There is growing evidence of a direct relationship between microbial community composition and function, which implies that distinct microbial communities vary in their functional ...properties. The aim of this study was to determine whether differences in initial substrate utilization between distinct microbial communities are due to the activities of certain microbial groups. We performed a short-term experiment with beech forest soils characterized by three different microbial communities (winter and summer community, and a community from a tree-girdling plot). We incubated these soils with different 13C-labelled substrates with or without inorganic N addition and analyzed microbial substrate utilization by 13C-phospholipid fatty acid (PLFA) analysis. Our results revealed that the fate of labile C (glucose) was similar in the three microbial communities, despite differences in absolute substrate incorporation between the summer and winter community. The active microbial community involved in degradation of complex C substrates (cellulose, plant cell walls), however, differed between girdling and control plots and was strongly affected by inorganic N addition. Enhanced N availability strongly increased fungal degradation of cellulose and plant cell walls. Our results indicate that fungi, at least in the presence of a high N supply, are the main decomposers of polymeric C substrates.
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Elemental stoichiometry constitutes an inherent link between biogeochemistry and the structure and processes within food webs, and thus is at the core of ecosystem functioning. Stoichiometry allows ...for spanning different levels of biological organization, from cellular metabolism to ecosystem structure and nutrient cycling, and is therefore particularly useful for establishing links between different ecosystem compartments. We review elemental carbon : nitrogen : phosphorus (C:N:P) ratios in terrestrial ecosystems (from vegetation, leaf litter, woody debris, and dead roots, to soil microbes and organic matter). While the stoichiometry of the plant, litter, and soil compartments of ecosystems is well understood, heterotrophic microbial communities, which dominate the soil food web and drive nutrient cycling, have received increasing interest in recent years.
This review highlights the effects of resource stoichiometry on soil microorganisms and decomposition, specifically on the structure and function of heterotrophic microbial communities and suggests several general patterns. First, latitudinal gradients of soil and litter stoichiometry are reflected in microbial community structure and function. Second, resource stoichiometry may cause changes in microbial interactions and community dynamics that lead to feedbacks in nutrient availability. Third, global change alters the C:N, C:P, and N:P ratios of primary producers, with repercussions for microbial decomposer communities and critical ecosystem services such as soil fertility. We argue that ecological stoichiometry provides a framework to analyze and predict such global change effects at various scales.
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Complete cycling of mineral nitrogen (N) in soil requires the interplay of microorganisms performing nitrification and denitrification, whose activity is increasingly affected by extreme rainfall or ...heat brought about by climate change. In a pristine forest soil, a gradual increase in soil temperature from 5 to 25 °C in a range of water contents stimulated N turnover rates, and N gas emissions were determined by the soil water-filled pore space (WFPS). NO and N₂O emissions dominated at 30% WFPS and 55% WFPS, respectively, and the step-wise temperature increase resulted in a threefold increase in the NO₃⁻ concentrations and a decrease in the NH₄⁺ concentration. At 70% WFPS, NH₄⁺ accumulated while NO₃⁻ pools declined, indicating gaseous N loss. AmoA- and nirK-gene-based analysis revealed increasing abundance of bacterial ammonia oxidizers (AOB) with increasing soil temperature and a decrease in the abundance of archaeal ammonia oxidizers (AOA) in wet soil at 25 °C, suggesting the sensitivity of the latter to anaerobic conditions. Denitrifier (nirK) community structure was most affected by the water content and nirK gene abundance rapidly increased in response to wet conditions until the substrate (NO₃⁻) became limiting. Shifts in the community structure were most pronounced for nirK and most rapid for AOA, indicating dynamic populations, whereas distinct adaptation of the AOB communities required 5 weeks, suggesting higher stability.
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Terrestrial microbial decomposer communities thrive on a wide range of organic matter types that rarely ever meet their elemental demands. In this review we synthesize the current state-of-the-art of ...microbial adaptations to resource stoichiometry, in order to gain a deeper understanding of the interactions between heterotrophic microbial communities and their chemical environment. The stoichiometric imbalance between microbial communities and their organic substrates generally decreases from wood to leaf litter and further to topsoil and subsoil organic matter. Microbial communities can respond to these imbalances in four ways: first, they adapt their biomass composition toward their resource in a non-homeostatic behavior. Such changes are, however, only moderate, and occur mainly because of changes in microbial community structure and less so due to cellular storage of elements in excess. Second, microbial communities can mobilize resources that meet their elemental demand by producing specific extracellular enzymes, which, in turn, is restricted by the C and N requirement for enzyme production itself. Third, microbes can regulate their element use efficiencies (ratio of element invested in growth over total element uptake), such that they release elements in excess depending on their demand (e.g., respiration and N mineralization). Fourth, diazotrophic bacteria and saprotrophic fungi may trigger the input of external N and P to decomposer communities. Theoretical considerations show that adjustments in element use efficiencies may be the most important mechanism by which microbes regulate their biomass stoichiometry. This review summarizes different views on how microbes cope with imbalanced supply of C, N and P, thereby providing a framework for integrating and linking microbial adaptation to resource imbalances to ecosystem scale fluxes across scales and ecosystems.
Background
Soil organic matter (SOM) is important for soil fertility and climate change mitigation. Agricultural management can improve soil fertility and contribute to climate change mitigation by ...stabilising carbon in soils. This calls for cost‐effective parameters to assess the influence of management practices on SOM contents.
Aims
The current study aimed at understanding how sensitively the parameters active carbon (AC) and nitrogen mineralisation potential (NMP) react to different agricultural management practices compared to total organic carbon (TOC) and total nitrogen (Nt). We aimed to gain a better understanding of SOM processes, mainly regarding depth distribution and seasonality of SOM dynamics using AC and NMP.
Methods
We looked mainly at four parameters, namely permanganate oxidisable carbon (AC), nitrogen minerlaisation potential (NMP), total organic carbon (TOC) and total nitrogen (Nt). Data were obtained in five long‐term field experiments (LTEs) testing four management practices: (1) tillage, (2) compost application, (3) crop residue management, and (4) mineral fertilization.
Results
AC was specifically sensitive in detecting the effect of tillage treatment at different soil depths. NMP differentiated between all different tillage treatments in the upper soil layer, it showed the temporal dynamics between the years in the compost LTE, and it was identified as an early detection property in the crop residue LTE. Both AC and NMP detected short‐term fluctuations better than TOC and Nt over the course of two years in the crop residue LTE.
Conclusion
We suggest that AC and NMP are two valuable soil biochemical parameters providing more detailed information on C and N dynamics regarding depth distribution and seasonal dynamics and react more sensitively to different agricultural management practices compared to TOC and Nt. They should be integrated in monitoring agricultural long‐term experiments (LTEs) and in field analyses conducted by farmers. However, when evaluating results towards long‐term carbon storage, their sensitivity toward annual fluctuations should be taken into account.
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