微塑料对稻田土壤温室气体排放和微生物群落的影响

微塑料因在土壤环境中广泛存在及其潜在的生态风险而受到越来越多的关注。微塑料的赋存会改变土壤理化性质,并对土壤微生物群落及其驱动的生物地球化学过程产生影响,而相关研究尚处于起步阶段。可生物降解塑料作为传统塑料的替代品,越来越多地应用于农业活动,并释放到土壤中。然而,可生物降解微塑料对土壤微生物特性产生影响的研究鲜有报道。基于此,本试验以我国三江平原水稻田土壤为研究对象,选取了2种常见的微塑料为试验材料,分别为传统型微塑料聚丙烯(Polypropylene,PP)和可降解微塑料聚乳酸(Polylactic acid,PLA),进行了为期41d的微宇宙培养实验,旨在分析不同浓度与类型的微塑料对土壤可溶性有机碳(Dissolved Organic Carbon,DOC)含量及官能团特征、温室气体排放以及微生物群落结构的差异性影响。结果表明,传统型微塑料PP与可降解微塑料PLA添加均对土壤理化性质与微生物群落产生显著影响。其中,微塑料添加大体上增加了土壤DOC含量,PLA的促进作用较为明显,且增加含量与微塑料添加量呈正相关;PP和PLA均影响土壤DOC分子结构,削弱了土壤团聚化程度并促进了大分子量DOC化合物的生成;微塑料的添加促进土壤CH₄排放,而有效抑制了土壤CO₂排放;微塑料显著改变了土壤细菌和真菌群落的丰富度与多样性。相关分析结果表明,土壤CO₂累计排放量与芳香族化合物结构及疏水性等官能团特征、变形菌门(Proteobacteria)与放线菌门(Actinobacteria)均呈显著正相关关系。以上结果表明,微塑料添加改变了土壤DOC含量及官能团特征与微生物环境,进而影响土壤温室气体排放。本研究为今后微塑料对土壤地球化学和微生物特性的影响研究提供了科学的思路,同时也有助于评估微塑料对土壤生态系统的生态风险。     

Infield greenhouse gas emissions from sugarcane soils in Brazil: effects from synthetic and organic fertilizer application and crop trash accumulation

Bioethanol from sugarcane is becoming an increasingly important alternative energy source worldwide as it is considered to be both economically and environmentally sustainable. Besides being produced from a tropical perennial grass with high photosynthetic efficiency, sugarcane ethanol is commonly associated with low N fertilizer use because sugarcane from Brazil, the world's largest sugarcane producer, has a low N demand. In recent years, several models have predicted that the use of sugarcane ethanol in replacement to fossil fuel could lead to high greenhouse gas (GHG) emission savings. However, empirical data that can be used to validate model predictions and estimates from indirect methodologies are scarce, especially with regard to emissions associated with different fertilization methods and agricultural management practices commonly used in sugarcane agriculture in Brazil. In this study, we provide in situ data on emissions of three GHG (CO₂, N₂O, and CH₄) from sugarcane soils in Brazil and assess how they vary with fertilization methods and management practices. We measured emissions during the two main phases of the sugarcane crop cycle (plant and ratoon cane), which include different fertilization methods and field conditions. Our results show that N₂O and CO₂ emissions in plant cane varied significantly depending on the fertilization method and that waste products from ethanol production used as organic fertilizers with mineral fertilizer, as it is the common practice in Brazil, increase emission rates significantly. Cumulatively, the highest emissions were observed for ratoon cane treated with vinasse (liquid waste from ethanol production) especially as the amount of crop trash on the soil surface increased. Emissions of CO₂ and N₂O were 6.9 kg ha^?1 yr^?1 and 7.5 kg ha^?1 yr^?1, respectively, totaling about 3000 kg in CO₂ equivalent ha^?1 yr^?1.     

Mediating N2O emissions from municipal solid waste landfills: Impacts of landfill operating conditions on community structure of ammonia-oxidizing bacteria in cover soils

Chemolithotrophic ammonia-oxidizing bacteria (AOB) can produce N₂O, a highly potent greenhouse gas. Denaturing gradient gel electrophoresis (DGGE) analyses of the ammonia monooxygenase structural gene (amoA) and 16S rDNA gene were used to investigate the AOB community structure in the cover soils of municipal solid waste (MSW) landfills under three operating conditions: (a) MSW with soil cover, (b) MSW with soil cover, irrigation piping and vegetation, and (c) MSW covered with high-density polyethylene (HDPE) liner, soil cover, irrigation piping and vegetation. AOB species in MSW cover soils were significantly distinguished by the operation of HDPE liner isolation. The community structures of the Nitrosomonas europaea-like AOB species dominated in soils without HDPE liner isolation, whether vegetation and irrigation with landfill leachate existed or not, whereas Nitrospira-like AOB species dominated in soils with HDPE liner isolation. Lower N₂O flux from the soils with HDPE liner isolation would be partially related to these special community structures.     

Influence of experimental extreme water pulses on greenhouse gas emissions from soils

Climate models predict increased frequency and intensity of storm events, but it is unclear how extreme precipitation events influence the dynamics of soil fluxes for multiple greenhouse gases (GHGs). Intact soil mesocosms (0–10 cm depth) from a temperate forested watershed in the piedmont region of Maryland [two upland forest soils, and two hydric soils (i.e., wetland, creek bank)] were exposed to experimental water pulses with periods of drying, forcing soils towards extreme wet conditions under controlled temperature. Automated measurements (hourly resolution) of soil CO₂, CH₄, and N₂O fluxes were coupled with porewater chemistry analyses (i.e., pH, Eh, Fe, S, NO₃ ^?), and polymerase chain reaction–denaturing gradient gel electrophoresis to characterize changes in microbial community structure. Automated measurements quantified unexpected increases in emissions up to 245% for CO₂ (Wetland), >23,000% for CH₄ (Creek), and >110,000% for N₂O (Forest Soils) following pulse events. The Creek soil produced the highest soil CO₂ emissions, the Wetland soil produced the highest CH₄ emissions, and the Forest soils produced the highest N₂O emissions during the experiment. Using carbon dioxide equivalencies of the three GHGs, we determined the Creek soil contributed the most to a 20-year global warming potential (GWP; 30.3%). Forest soils contributed the most to the 100-year GWP (up to 53.7%) as a result of large N₂O emissions. These results provide insights on the influence of extreme wet conditions on porewater chemistry and factors controlling soil GHGs fluxes. Finally, this study addresses the need to test biogeochemical thresholds and responses of ecosystem functions to climate extremes.     

Salinity effects on greenhouse gas emissions from wetland soils are contingent upon hydrologic setting: a microcosm experiment

Coastal forested wetlands provide important ecosystem services such as carbon sequestration, nutrient retention, and flood protection, but they are also important sources of greenhouse gas emissions. Human appropriation of surface water and extensive ditching and draining of coastal plain landscapes are interacting with rising sea levels to increase the frequency and magnitude of saltwater incursion into formerly freshwater coastal wetlands. Both hydrologic change and saltwater incursion are expected to alter carbon and nutrient cycling in coastal forested wetlands. We performed a full factorial experiment in which we exposed intact soil cores from a coastal forested wetland to experimental marine salt treatments and two hydrologic treatments. We measured the resulting treatment effects on the emissions of carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) over 112 days. Salinity effects were compared across four treatments to isolate the effects of increases in ionic strength from the impact of adding a terminal electron acceptor (SO₄^2?). We compared control treatments (DI addition), to artificial saltwater (ASW, target salinity of 5 parts per thousand) and to two treatments that added sulfate alone (SO₄^2?, at the concentration found in 5 ppt saltwater) and saltwater with the sulfate removed (ASW-SO₄^2?, with the 5 ppt target salinity maintained by adding additional NaCl). We found that all salt treatments suppressed CO₂ production, in both drought and flooded treatments. Contrary to our expectations, CH₄ fluxes from our flooded cores increased between 300 and 1200% relative to controls in the ASW and ASW-SO₄^2? treatments respectively. In the drought treatments, we saw virtually no CH₄ release from any core, while artificial seawater with sulfate increased N₂O fluxes by 160% above DI control. In contrast, salt and sulfate decreased N₂O fluxes by 72% in our flooded treatments. Our results indicate that salinization of forested wetlands of the coastal plain may have important climate feedbacks resulting from enhanced greenhouse gas emissions and that the magnitude and direction of these emissions are contingent upon wetland hydrology.     

Microbial sensitivity to temperature and sulfate deposition modulates greenhouse gas emissions from peat soils

Peatlands are among the largest natural sources of atmospheric methane (CH₄) worldwide. Microbial processes play a key role in regulating CH₄ emissions from peatland ecosystems, yet the complex interplay between soil substrates and microbial communities in controlling CH₄ emissions as a function of global change remains unclear. Herein, we performed an integrated analysis of multi-omics data sets to provide a comprehensive understanding of the molecular processes driving changes in greenhouse gas (GHG) emissions in peatland ecosystems with increasing temperature and sulfate deposition in a laboratory incubation study. We sought to first investigate how increasing temperatures (4, 21, and 35°C) impact soil microbiome–metabolome interactions; then explore the competition between methanogens and sulfate-reducing bacteria (SRBs) with increasing sulfate concentrations at the optimum temperature for methanogenesis. Our results revealed that peat soil organic matter degradation, mediated by biotic and potentially abiotic processes, is the main driver of the increase in CO₂ production with temperature. In contrast, the decrease in CH₄ production at 35°C was linked to the absence of syntrophic communities and the potential inhibitory effect of phenols on methanogens. Elevated temperatures further induced the microbial communities to develop high growth yield and stress tolerator trait-based strategies leading to a shift in their composition and function. On the other hand, SRBs were able to outcompete methanogens in the presence of non-limiting sulfate concentrations at 21°C, thereby reducing CH₄ emissions. At higher sulfate concentrations, however, the prevalence of communities capable of producing sufficient low-molecular-weight carbon substrates for the coexistence of SRBs and methanogens was translated into elevated CH₄ emissions. The use of omics in this study enhanced our understanding of the structure and interactions among microbes with the abiotic components of the system that can be useful for mitigating GHG emissions from peatland ecosystems in the face of global change.     

Current available strategies to mitigate greenhouse gas emissions in livestock systems: an animal welfare perspective

Livestock production is a major contributor to greenhouse gas (GHG) emissions, so will play a significant role in the mitigation effort. Recent literature highlights different strategies to mitigate GHG emissions in the livestock sector. Animal welfare is a criterion of sustainability and any strategy designed to reduce the carbon footprint of livestock production should consider animal welfare amongst other sustainability metrics. We discuss and tabulate the likely relationships and trade-offs between the GHG mitigation potential of mitigation strategies and their welfare consequences, focusing on ruminant species and on cattle in particular. The major livestock GHG mitigation strategies were classified according to their mitigation approach as reducing total emissions (inhibiting methane production in the rumen), or reducing emissions intensity (Ei; reducing CH₄ per output unit without directly targeting methanogenesis). Strategies classified as antimethanogenic included chemical inhibitors, electron acceptors (i.e. nitrates), ionophores (i.e. Monensin) and dietary lipids. Increasing diet digestibility, intensive housing, improving health and welfare, increasing reproductive efficiency and breeding for higher productivity were categorized as strategies that reduce Ei. Strategies that increase productivity are very promising ways to reduce the livestock carbon footprint, though in intensive systems this is likely to be achieved at the cost of welfare. Other strategies can effectively reduce GHG emissions whilst simultaneously improving animal welfare (e.g. feed supplementation or improving health). These win–win strategies should be strongly supported as they address both environmental and ethical sustainability. In order to identify the most cost-effective measures for improving environmental sustainability of livestock production, the consequences of current and future strategies for animal welfare must be scrutinized and contrasted against their effectiveness in mitigating climate change.     

Effects of nitrogen deposition on the greenhouse gas fluxes from forest soils

Nitrogen (N) deposition can alter the rates of microbial N- and C- turnover, and thus can affect the fluxes of greenhouse gases (GHG, e.g., CO₂, CH₄, and N₂O) from forest soils. The effects of N deposition on the GHG fluxes from forest soils were reviewed in this paper. N deposition to forest soils have shown variable effects on the soil GHG fluxes from forest, including increases, decreases or unchanged rates depending on forest type, N status of the soil, and the rate and type of atmospheric N deposition. In forest ecosystems where biological processes are limited by N supply, N additions either stimulate soil respiration or have no significant effect, whereas in “N saturated” forest ecosystems, N additions decrease CO₂ emission, reduce CH₄ oxidation and elevate N₂O flux from the soil. The mechanisms and research methods about the effects of N deposition on GHG fluxes from forest soils were also reviewed in this paper. Finally, the present and future research needs about the effects of N deposition on the GHG fluxes from forest soils were discussed.     

氮沉降对森林土壤主要温室气体通量的影响

大气氮沉降已经并将继续对森林土壤主要温室气体(CO2、CH4和N2O)通量产生影响.综述了国内外氮沉降对森林土壤主要温室气体通量影响及其机理的研究现状.由于森林类型、土壤N状况、氮沉降量及沉降类型等不同,氮沉降对森林土壤主要温室气体通量的影响主要表现为抑制、促进和不显著3种效果.在N限制的森林中,氮沉降对土壤主要温室气体通量无显著影响,或促进土壤CO2排放;在"N饱和"的森林中,氮沉降可减少土壤CO2排放,抑制对大气CH4的吸收,增加N2O排放.分析了产生以上影响效果的作用机理,介绍了氮沉降对森林土壤主要温室气体通量影响的研究方法,探讨了该领域存在的问题及未来研究的方向.     

Linking soil N2O emissions with soil microbial community abundance and structure related to nitrogen cycle in two acid forest soils

Plant and Soil - Tree species and seasonal change influence N2O flux and microbial communities, but the mechanisms are unclear. We studied N2O flux in soils planted with slash pine and oil-seed...     

Diversity and activity of methanotrophs in landfill cover soils with and without landfill gas recovery systems

Aerobic CH₄ oxidation plays an important role in mitigating CH₄ release from landfills to the atmosphere. Therefore, in this study, oxidation activity and community of methanotrophs were investigated in a subtropical landfill. Among the three sites investigated, the highest CH₄ concentration was detected in the landfill cover soil of the site (A) without a landfill gas (LFG) recovery system, although the refuse in the site had been deposited for a longer time (∼14–15 years) compared to the other two sites (∼6–11 years) where a LFG recovery system was applied. In April and September, the higher CH₄ flux was detected in site A with 72.4 and 51.7 g m⁻² d⁻¹, respectively, compared to the other sites. The abundance of methanotrophs assessed by quantification of pmoA varied with location and season. A linear relationship was observed between the abundance of methanotrophs and CH₄ concentrations in the landfill cover soils (R = 0.827, P < 0.001). The key factors influencing the methanotrophic diversity in the landfill cover soils were pH, the water content and the CH₄ concentration in the soil, of which pH was the most important factor. Type I methanotrophs, including Methylococcus, Methylosarcina, Methylomicrobium and Methylobacter, and type II methanotrophs (Methylocystis) were all detected in the landfill cover soils, with Methylocystis and Methylosarcina being the dominant genera. Methylocystis was abundant in the slightly acidic landfill cover soil, especially in September, and represented more than 89% of the total terminal-restriction fragment abundance. These findings indicated that the LFG recovery system, as well as physical and chemical parameters, affected the diversity and activity of methanotrophs in landfill cover soils.     

Interplay between yield,nitrogen application,and logistics on the potential energetic and greenhouse gas emissions from biomass crops

The interplay between nitrogen fertilization (N), yield, nitrous oxide emissions (N₂O), and diesel fuel utilization associated with harvest and transport logistics of biomass crops remains poorly understood. In this research, we show that intensification (in terms of N) of bioenergy cropping to maximize yield supports not only minimized land use but also maximized logistics efficiency in terms of diesel use. This paradigm was examined within the scope of the billion‐ton biofuels vision and the Energy Independence and Security Act of 2007 using potential yields on marginal and prime agricultural land. Sixteen scenarios were investigated that considered the primary factors with agriculture bioenergy; biomass yield (11.2 and 22.4 Mg ha^?1 yr^?1), two nitrogen fertilizer application rates (50 and 100 kg N ha^?1 yr^?1), two Greenhouse Gas Emissions (GHGE) factors for synthetic nitrogen to nitrous oxide (1.5 and 5%), and three harvest/transportation efficiencies (50, 65, and 80%). These scenarios resulted in energy consumption between 747 and 1351 MJ Mg^?1 and GHGE between 72 and 311 kg CO₂ eq Mg^?1. GHGE emissions are strongly related to the emission of nitrous oxide from soils due to nitrogen fertilization and could represent over 80% of the GHGE relative to biomass harvest logistics. These data imply that synthetic N supplementation to maximize yield could reduce the burden due to diesel fuel for harvest, but would rapidly become the most significant contributor to GHGE. Minimizing the impact of N fertilization will be critical for reducing the GHGE associated with biomass production.     

Temperature dependence of greenhouse gas emissions from three hydromorphic soils at different groundwater levels

Wetlands contribute considerably to the global greenhouse gas (GHG) balance. In these ecosystems, groundwater level (GWL) and temperature, two factors likely to be altered by climate change, exert important control over CO₂, CH₄ and N₂O fluxes. However, little is known about the temperature sensitivity (Q₁₀) of the combined GHG emissions from hydromorphic soils and how this Q₁₀ varies with GWL. We performed a greenhouse experiment in which three different (plant‐free) hydromorphic soils from a temperate spruce forest were exposed to two GWLs (an intermediate GWL of ?20 cm and a high GWL of ?5 cm). Net CO₂, CH₄ and N₂O fluxes were measured continuously. Here, we discuss how these fluxes responded to synoptic temperature fluctuations. Across all soils and GWLs, CO₂ emissions responded similarly to temperature and Q₁₀ was close to 2. The Q₁₀ of the CH₄ and N₂O fluxes also was similar across soil types. GWL, on the other hand, significantly affected the Q₁₀ of both CH₄ and N₂O emissions. The Q₁₀ of the net CH₄ fluxes increased from about 1 at GWL = ?20 cm to 3 at GWL = ?5 cm. For the N₂O emissions, Q₁₀ varied around 2 for GWL = ?20 cm and around 4 for GWL = ?5 cm. This substantial GWL‐effect on the Q₁₀ of CH₄ and N₂O emissions was, however, hardly reflected in the Q₁₀ of the total GHG emissions (which varied around 2), because the contribution of these gases was relatively small compared to that of CO₂.     

模拟氮沉降对藏北高寒草甸温室气体排放的影响

目前,高寒草甸对全球温室效应的贡献仍具有不确定性,而随着N沉降的增加,该系统温室体气排放也必将发生变化。为揭示高寒草甸对N沉降的响应机制,探讨其对全球变化的反馈作用,利用人工添加氮素的方法,于2014年生长季(6-9月)在那曲地区那曲县设置不同水平N添加梯度(0、7、20kg hm~(-2)a~(-1)和40 kg hm~(-2)a~(-1)),模拟氮沉降增加对藏北高寒草甸温室气体排放的影响。经过1a的研究结果表明:1)施氮显著促进了CO_2排放但对CH_4的吸收和N_2O的排放无显著影响。总体而言,添加氮素明显增加了温室气体排放总量,其中N2O处理下高寒草甸温室气体排放总量最高。2)回归分析结果表明,CO_2与NPP(总生物量)和TOC(土壤有机碳)线性相关(P0.05),而与TN(总氮)、NH_4~+-N和NO_3~--N均无显著相关关系(P0.05),CH_4与TN/NPP/TOC/NH_4~+-N/NO_3~--N均不相关(P0.05),N_2O与NPP/TOC/NO_3~--N均显著线性相关(P0.05),而与TN/NH_4~+-N不相关。综合初步研究结果,未来氮沉降增加条件下,藏北高寒草甸温室气体排放通量将有可能明显增加,从而对气候变化产生重要的反馈作用。     

设施菜田与棚外粮田土壤菌群和反硝化气体产生的比较分析

【目的】对比设施菜田与棚外粮田土壤菌群以及N2O产生模式的差异。【方法】采用变性梯度凝胶电泳(DGGE)和反硝化功能基因(nirS,nosZ)方法分别比较两种土壤细菌群落以及功能基因类群丰度的差异,利用自动连续在线培养监测体系(Robot系统)测定两种土壤在好氧、厌氧阶段N2O等反硝化相关气态产物产生模式,分析N2O/(N2+N2O+NO)产物比。【结果】设施菜田与棚外粮田具有不同的土壤细菌群落结构,并且土壤细菌总量得到了显著的提升,然而两种反硝化功能基因(nirS,nosZ)丰度并没有显著变化。与设施菜田相比,棚外粮田有相对低的N2O积累量以及产物比,并且在厌氧初期气体产生模式有所不同。培养后铵态氮和亚硝态氮含量上升。【结论】设施菜田长期有别于棚外粮田的管理方式造成了土壤细菌群落的显著改变,增大了活跃微生物总量,造成土壤酸化,并导致N2O在气态产物中的比例升高。设施菜田土壤微生物进行了与棚外粮田不同的硝酸盐呼吸过程,异化硝酸盐还原成铵(DNRA)过程有可能贡献了两种土壤的部分厌氧N2O产生量。     

Heat‐wave effects on greenhouse gas emissions from shallow lake mesocosms

相似文献   

Effect of improved nitrogen management on greenhouse gas emissions from intensive dairy systems in the Netherlands

Dairy systems in Europe contribute to the emissions of the greenhouse gases (GHGs) nitrous oxide (N₂O), methane (CH₄) and carbon dioxide (CO₂). In this paper, the effects of improved nitrogen (N) management on GHG emissions from Dutch dairy farms are determined. The GHG emissions are calculated using the panel on climate change (IPCC) methodology for the Netherlands, an updated and refined IPCC methodology, and a full accounting approach. The changes in dairy farming over the last 20 years, and the consequences for N management are described using detailed farm‐level data, collected in 1985, 1997 and 2002. The selected years represent distinct stages in the implementation of N policies. The changes in N management have reduced the GHG emissions. A reduction of the N surplus per kilogram milk with 1 g N reduced the GHG emissions per kilogram milk with approximately 29 g CO₂‐equivalents. The reduction of the N surpluses was mainly brought about by reduced fertilizer use and reduced grazing time. The use of updated and refined emission factors resulted in higher CH₄ emissions and lower N₂O emissions. On average, the overall emission was 36% higher with the refined method. Full accounting, including all direct and indirect emissions of CH₄, N₂O and CO₂, increased the emission with 36% compared with the refined IPCC methodology. We conclude that the N surplus at farm level is a useful indicator of GHG emissions. A full accounting system as presented in this study may effectively enable farmers to address the issue of emissions of GHGs in their operational management decisions. Both approaches serve their own specific objectives: full accounting at the farm level to explore mitigation options, and the IPCC methods to report changes in GHG emissions at the national level.     

Prediction of effects of beef selection indexes on greenhouse gas emissions

Genetic improvement in production efficiency traits can also drive reduction in greenhouse gas emissions. This study used international ‘best-practice’ methodology to quantify the improvements in system-wide CO₂ equivalent emissions per unit of genetic progress in the Irish Maternal Replacement (MR) and Terminal (T) beef cattle indexes. Effects of each index trait on system gross emissions (GE) and system emissions intensity (EI) were modelled by estimating effects of trait changes on per-animal feed consumption and associated methane production, per-animal meat production and numbers of animals in the system. Trait responses to index selection were predicted from linear regression of individual bull estimated breeding values for each index trait on their MR or T index value, and the resulting regression coefficients were used to calculate trait-wise responses in GE and EI from index selection. Summed over all trait responses, the MR index was predicted to reduce system GE by 0.810 kg CO₂e/breeding cow per year per € index and system EI by 0.009 kg CO₂e/kg meat per breeding cow per year per € index. These reductions were mainly driven by improvements in cow survival, reduced mature cow maintenance feed requirements, shorter calving interval and reduced offspring mortality. The T index was predicted to reduce system EI by 0.021 kg CO₂e/kg meat per breeding cow per year per € index, driven by increased meat production from improvements in carcass weight, conformation and fat. Implications for incorporating an EI reduction index to the current production indexes and long-term projections for national breeding programs are discussed.     

The effects of stubble retention and nitrogen application on soil microbial community structure and functional gene abundance under irrigated maize

The effects of agronomic management practices on the soil microbial community were investigated in a maize production system in New South Wales, Australia. The site has been intensively studied to measure the impact of stubble management and N-fertilizer application on greenhouse gas emissions (CO(2) and N(2)O), N-cycling, pathology, soil structure and yield. As all of these endpoints can be regulated by microbial processes, the microbiology of the system was examined. Soil samples were taken after a winter fallow period and the diversity of the bacterial and fungal communities was measured using PCR-denaturing gradient gel electrophoresis. Stubble and N shifted the structure of bacterial and fungal communities with the primary driver being stubble addition on the fungal community structure (P<0.05 for all effects). Changes in C, N (total and NO(3)), K and Na, were correlated (P<0.05) with variation in the microbial community structure. Quantitative PCR showed that nifH (nitrogen fixation) and napA (denitrification) gene abundance increased upon stubble retention, whereas amoA gene numbers were increased by N addition. These results showed that the management of both stubble and N have significant and long-term impacts on the size and structure of the soil microbial community at phylogenetic and functional levels.