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Soil fungi can differentially affect plant performance and community dynamics. While fungi play key roles in driving the plant-soil feedbacks (PSFs) that promote grassland succession, it remains unclear how the fungi-mediated PSFs affect tree species establishment during forest succession. We inoculated pioneer broadleaf (Betula platyphylla and Betula albosinensis) and nonpioneer coniferous tree seedlings (Picea asperata and Abies faxoniana) with fungal-dominated rooting zone soils collected from dominant plant species of early-, mid- and late-successional stages in a subalpine forest, and compared their biomass and fungal communities. All tree species accumulated abundant pathogenic fungi in early-successional inoculated soil, which generated negative biotic feedbacks and lowered seedling biomass. High levels of soil ectomycorrhizal fungi from mid- and late-successional stages resulted in positive biotic PSFs and strongly facilitated slow-growing coniferous seedling performance to favour successional development. B. albosinensis also grew better in mid- and late-successional soils with fewer pathogenic fungi than in early-successional soil, indicating its large susceptibility to pathogen attack. In contrast, the growth of another pioneer tree, B. platyphylla, was significantly suppressed in late-successional soil and was mostly driven by saprotrophic fungi, despite the unchanged pathogenic fungal community traits between the two fast-growing species. This unexpected result suggested a host specificity-dependent mechanism involved in the different impacts of fungal pathogens on host trees. Our findings reveal a critical role of functional shifts in soil fungal communities in mediating differential PSFs of tree species across successional stages, which should be considered to improve the prediction and management of community development following forest disturbances.

Fast-growing pioneer tree species play a crucial role in triggering late successional development in forests. Experimental evidence of the soil legacy effects of pre-existing plants on pioneer tree performance is lacking. We explored the legacy effects of soils conditioned by early successional herbs (Poa poophagorum Bor and Potentilla fragarioides L.) and mid-successional shrubs (Rhododendron fortunei Lindl. and Enkianthus quinqueflorus Lour.) on late-successional ectomycorrhizal (ECM) pioneer tree (Betula platyphylla Sukaczev) seedling growth. The soils were analyzed for soil nutrient status and fungal and bacterial compositions using ITS and 16S rRNA gene sequencing. B. platyphylla seedlings produced higher biomass in soils conditioned by shrubs. Soil organic carbon (SOC) and bacterial and fungal legacies most impacted pioneer tree seedling growth. Additionally, the partial least squares path model revealed that soil nutrients, especially SOC, indirectly affected seedling biomass by their direct effects on the bacterial and fungal communities. The changes in bacterial community composition had a stronger effect on seedling biomass than those of fungi because bacteria with shorter turnover times are generally considered to be more efficient than fungi in enhancing nutrient availability. Our study integrates soil microbial and nutrient legacies to explain the potential mechanisms of pioneer tree regeneration.

The assembly mechanisms shaping the elevational patterns of diversity and community structure in ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) are not well understood. We investigated the diversities, co-occurrence network patterns, key drivers, and potential activities of AOA and AOB communities along a large altitudinal gradient. The α-diversity of the AOA communities exhibited a monotonically decreasing pattern with increasing elevation, whereas a sinusoidal pattern was observed for the AOB communities. The mean annual temperature was the single factor that most strongly influenced the α-diversity of the AOA communities; however, the interactions of plant richness, soil conductivity, and total nitrogen made comparable contributions to the α-diversity of the AOB communities. Moreover, the β-diversities of the AOA and AOB communities were divided into two distinct clusters by elevation, i.e., low- (1800-2600 m) and high-altitude (2800-4100 m) sections. These patterns were attributed mainly to the soil pH, followed by variations in plant richness along the altitudinal gradient. In addition, the AOB communities were more important to the soil nitrification potential in the low-altitude section, whereas the AOA communities contributed more to the soil nitrification potential in the high-altitude section. Overall, this study revealed the key factors shaping the elevational patterns of ammonia-oxidizing communities and might predict the consequences of changes in ammonia-oxidizing communities.

While large differences in microbial biomass and extracellular enzyme activities (EEAs) between rhizosphere and bulk soils have been demonstrated, the potentially different response of microbes and their EEAs in rhizosphere and bulk soils to nitrogen (N) deposition is still not elucidated. We analyzed the microbial biomass and EEAs in the rhizosphere and bulk soils of Sibiraea angustata in an alpine shrubland on the eastern Qinghai-Tibet Plateau after chronic N application. We also analyzed the stoichiometric linkages between plants, microbes, enzymes and soils to clarify the coupled responses of aboveground plants and belowground ecological processes. Microbial nutrient concentrations and activities of EAAs responded differently to N addition in the rhizosphere and bulk soils. In the rhizosphere, N addition caused a significant increase in microbial biomass carbon (C), N and phosphorus (P) concentrations and greater P-degrading enzyme activity (relative to the activities of C- and N-degrading enzymes), which induced a significant reduction in enzyme C:P and N:P ratios. The rhizosphere enzyme N:P ratio was negatively correlated with the N:P ratios of plant, soil and microbe, implying that increased plant and microbial P uptake under N addition may gradually aggravate rhizosphere P limitation. However, for the bulk soil, N addition did not affect microbial biomass but significantly enhanced C-degrading enzyme activity and decreased the enzyme C:N ratio. Meanwhile, the bulk-soil enzyme C:N ratio was negatively correlated with the soil C:N ratio but independent of the plant C:N ratio, implying that N addition may enhance bulk-soil microbial C limitation. Our study suggests that elevated N deposition may induce differential microbial nutrient limitation between the rhizosphere and bulk soils due to the plant-microbe-soil interactions in the rhizosphere. This study highlights the importance of incorporating rhizosphere microbial processes into biogeochemical models describing environmental changes.

nirK-type and nirS-type denitrifier communities mediate the conversion of nitrite to nitric oxide, which is the key step in denitrification. Results of previous studies have indicated that nirK-type and nirS-type denitrifiers may occupy different niches; however, the mechanisms and drivers of their responses to environmental changes within community assembly are poorly understood. In this study, we evaluated the distribution and assembly of nirK-type and nirS-type denitrifier communities along an elevation gradient from 1,800 to 4,100 m at Mount Gongga, China. Results showed that elevational patterns of alpha diversity in nirK-type and nirS-type denitrifier communities followed hump-backed patterns along the elevation gradient. However, nirK-type denitrifier communities formed two distinct clusters that were primarily separated by elevation, whereas nirS-type denitrifier communities formed three distinct clusters that were primarily separated by forest type along the elevation gradient. Moreover, deterministic processes were dominant in governing the assemblages of nirK-type and nirS-type denitrifiers. Soil pH was a key factor influencing the alpha and beta diversity of the nirK-type denitrifier communities, whereas plant richness was a primary variable influencing nirS-type denitrifiers. Additionally, our work revealed that soil denitrification potential was mainly explained by the variation in the beta diversity of denitrifier communities rather than the alpha diversity of denitrifier communities or denitrifier abundances over a large elevation gradient, and nirK-type denitrifiers played more important roles in soil denitrification. These results may contribute to predicting the consequences of global changes on denitrifier communities and their ecological services. IMPORTANCE Mount Gongga is the highest peak in the Hengduan Mountain region and is located at the southeastern fringe of the Tibetan Plateau, Sichuan Province, southwest China. As a transitional zone between the Tibetan Plateau and Sichuan Basin, Gongga Mountain features particularly diverse topography, geology, climate, and biodiversity and is a globally significant hot spot of biodiversity. In this contribution, we comprehensively describe the diversity and assembly of denitrifier communities along an elevation gradient on Gongga Mountain. Our findings established for the first time that the distribution patterns of beta diversity and driving factors differed between nirK-type and nirS-type denitrifier communities, and deterministic processes were dominant in shaping communities of denitrifiers. Moreover, the beta diversity of denitrifier communities rather than alpha diversity or denitrifier abundance played an important role in explaining denitrification potential, and the beta diversity of nirK-type denitrifier communities was more important than nirS-type denitrifier communities in soil denitrification. This work provides crucial insights into the spatial distribution of denitrifier communities and their ecological function and increases our understanding of the mechanisms underlying spatial distribution of community assembly along large elevation gradients.

Ectomycorrhizal fungi (EcMF) are involved in soil nutrient cycling in forest ecosystems. These fungi can promote the uptake of nutrients (e.g., nitrogen (N) and phosphorus (P)) and water by host plants, as well as facilitate host plant growth and resistance to stresses and diseases, thereby maintaining the aboveground primary productivity of forest ecosystems. Moreover, EcMF can acquire the carbon (C) sources needed for their growth from the host plants. The nutrient regulation mechanisms of EcMF mainly include the decay of soil organic matter via enzymatic degradation, nonenzymatic mechanism (Fenton chemistry), and priming effects, which in turn promote C and N cycling. At the same time, EcMF can secrete organic acids and phosphatases to improve the availability of soil P, or increase mycelium inputs to facilitate plant acquisition of P. The spatiotemporal distribution of EcMF is influenced by a combination of historical factors and contemporary environmental factors. The community of EcMF is associated with various factors, such as climate change, soil conditions, and host distribution. Under global climate change, investigating the relationships between the nutrient cycling functions of EcMF communities and their distribution patterns under various spatiotemporal scales is conducive to more accurate assessments of the ecological effects of EcMF on the sustainable development of forest.

Understanding microbial network assembly is a promising way to predict potential impacts of environmental changes on ecosystem functions. Yet, soil microbial network assembly in mountain ecosystems and its underlying mechanisms remain elusive. Here, we characterized soil microbial co-occurrence networks across 12 altitudinal sites in Mountain Gongga. Despite differences in habitats, soil bacterial networks separated into two different clusters by altitude, namely the lower and higher altitudes, while fungi did not show such a pattern. Bacterial networks encompassed more complex and closer relationships at the lower altitudes, while fungi had closer relationships at the higher altitudes, which could be attributed to niche differentiation caused by high variations in soil environments and plant communities. Both abiotic and biotic factors (e.g. soil pH and bacterial community composition) shaped bacterial networks. However, biotic factors played more important roles than the measured abiotic factors for fungal network assembly. Further analyses suggest that multiple mechanisms including niche overlap/differentiation, cross-feeding and competition between microorganisms could play important roles in shaping soil microbial networks. This study reveals microbial co-occurrence networks in response to different ecological factors, which provides important insights into our comprehensive understanding of microbial network assembly and their functional potentials in mountain ecosystems.

Background Gut microbial shifts have great potential to predict the risk of colorectal cancer, but how gut microbes respond to the development of colorectal cancer in males and females at the community scale is unknown. To address this question, we reanalyzed the dataset from a published project and grouped these data depending on sex into three groups, healthy, colorectal adenoma and carcinoma individuals, and community assembly and network patterns of gut microbes were evaluated by null model and co-occurrence network-based methods. Results The study showed that distinct changes in microbial α -diversities and community composition were observed between the male and female gut. Specifically, the microbial α -diversities did not significantly change in the male gut ( P > 0.05) but were lowered in the female gut ( P < 0.05), suggesting that permanent species loss might occur in the female gut during the development of colorectal cancer. These distinct changes in microbial α -diversities and community composition between the male and female gut might result from host immunity mechanisms and different microbial community assemblies in males and females. Indeed, we found that the microbial community tended to be primarily stochastic in males, whereas it became increasingly deterministic in females with the development of colorectal cancer. Moreover, microbial co-occurrence associations tended to be more complicated when communities were primarily driven by stochastic processes in males; rare species were enriched in the co-occurrence network of the male gut, whereas key species loss was observed in the co-occurrence network of the female gut. Conclusions Our findings indicate that microbial communities in the male gut are more stable than those in the female gut and that microbial community assembly in the gut is sex-dependent with the development of colorectal cancer. Our study suggests that sexual dimorphism needs to be taken into account to better predict the risk of colorectal cancer based on microbial shifts.

Application of the inhibitor-amended nitrogen fertilizers is a recommended method for reducing agricultural nitrous oxide (N2O) emission. However, the potential impacts of these inhibitors on soil environments still needs to be evaluated using long-term experiments. Through a 6-year field observation, the effects of combined application of a nitrification inhibitor (dicyandiamide, DCD) and a urease inhibitor (hydroquinone, HQ) on N2O emission, as well as soil ammonia oxidizers and denitrifiers in a maize (Zea mays L.) field in Northeast China were investigated. The results showed that annual soil N2O emissions were 0.466, 1.021 and 0.874 kg N2O-N ha−1 for N0 fertilizer treatment (CK), Urea treatment (U) and Urea + DCD + HQ treatment (UDH), respectively. A significant linear correlation was found between the N2O accumulation in the first month after fertilizer application and the short-term precipitation (i.e., a period from 10 days before to 20 days after fertilizer application). The N2O emissions in the freeze-thaw period accounted for up to 42.5% of the year-round N2O emissions. The remarkable fluctuations of annual N2O emissions were observed (their coefficients of variation were 68.3%, 77.7% and 71.2% for CK, U and UDH treatments, respectively); these fluctuations were mainly attributed to the precipitation. The averaged N2O emission factors (EF) (0.308% and 0.227% for U and UDH treatments, respectively) were far less than the default mean EF of 1% proposed by ( IPCC, 2006 ). An averaged N2O mitigation of 26.4% was fulfilled by UDH application. The results of quantitative PCR for soil nitrification and denitrification gene copy numbers measurement showed that UDH treatment significantly decreased the ammonia oxidation bacteria (AOB) amoA gene copy numbers by 74% on the 10th day after UDH application. No significant effects of combined application of DCD and HQ on microbial denitrification functional gene abundance were observed.

Based on the contemporary coexistence theory developed from macroecology, the regional species pool, environmental processes, dispersal assembly and biotic interactions are considered to determine the assembly of a local community. However, we do not fully understand whether these kinds of mechanisms are all-important for the whole microbial community or for specific functional groups. Here we studied the underlying processes driving the β-diversity of soil-based diazotrophic communities across a large geographical distance in Chinese grasslands by considering the roles of species pools and ecological assembly processes. Results indicated that the species pool (γ-diversity) showed significant and positive correlations to the observed β-diversity of the diazotrophic community; that is, diazotrophic community turnover increased with the size of the species pool. Environmental filtering played a greater role than dispersal effects or biotic interactions on β-diversity. Biotic interactions drove the assemblage of diazotrophs by influencing the co-occurrence pattern of species. Overall, these results demonstrated the importance of the species pool and local community assembly processes in shaping diazotrophic β-diversity patterns in grassland soils.

The biological nitrogen input is essential for nutrient enrichment in natural grassland ecosystems. This process is carried out by diazotrophic microbes. However, the patterns and assembly processes of diazotrophic communities in grassland soil are not fully understood, especially in alpine meadows of high-altitude Qinghai-Tibet Plateau (QTP). In this study, the diversity patterns and community assembly processes of soil diazotrophic communities were investigated in QTP alpine meadows. The results showed that different diazotrophic taxa responded differentially to the increase of soil pH, and α-diversity increased linearly with pH values. Diazotrophic community turnover was enhanced by the increased variation in soil pH, moreover, it also showed strong response to mean annual temperature. Null model analysis showed that deterministic processes were most important in shaping the phylogenetic community structure and assembly of diazotrophs. Diazotrophic communities of each sampling site tended to be phylogenetically clustered, while communities at high pH soils (pH 7.00 to 8.00) showed more clustering than those of low pH (pH 5.02 to 7.00). The soil pH is a main driver in structuring soil diazotrophic community assembly by regulating the relative importance of deterministic and stochastic processes in QTP alpine meadows.

Methane (CH4) oxidation plays a critical role in mitigating global warming. However, the key environmental drivers shaping CH4 oxidation rate at regional and sub-regional scales in grassland ecosystems remain poorly understood. In this study, we collected soils from 21 sites at the regional scale across three steppes of China, including grasslands in Inner Mongolia Plateau (IMP), Xinjiang Autonomous Region (XAR) and Tibetan Plateau (TP). Potential CH4 oxidation rate was measured, and the compositions and abundances of methanotrophs were analyzed by quantitative PCR (qPCR) and Miseq sequencing technique. The factors controlling CH4 oxidation potential at regional and sub-regional scales were evaluated by means of partial least squares path modeling (PLS-PM) and multiple regression on distance matrices (MRM). The results showed that the compositions and abundances of methanotrophs varied at different sub-regions. Type I methanotrophs were predominant in soils from the Inner Mongolia steppe and Xinjiang Autonomous Region, whereas pxmA methanotrophs mainly distributed in the Tibetan alpine steppe soil. Measured environmental variables explained the variations of CH4 oxidation potential well at both regional and sub-regional scales in these Chinese grassland ecosystems. However, the contributions of different variables to CH4 oxidation potential were scale-dependent. At the regional scale, total nitrogen (TN) was the environmental variable that best explained the potential CH4 oxidation rate, and its influence might be mainly associated with its effects on plant growth and methanotrophic community traits. At sub-regional scales, the main controlling variables were total organic carbon (TOC) and soil texture in Inner Mongolia steppe, aridity index (AI) and mean annual temperature (MAT) in Xinjiang Autonomous Region, and TN in Tibetan alpine steppe. These results further suggested that the impacts of environmental variables on CH4 oxidation rate were realized either through their effects on methanotrophic communities, and/or by affecting soil properties in the grassland ecosystems.

The mammalian stomach acts as an important barrier against ingested pathogens into the entire gastrointestinal tract, thereby playing a key role in host health. However, little is known regarding to the stomach microbial compositions in wild mammals and the factors that may influence the community compositions. Using high-throughput sequencing of the 16S rRNA gene, we characterized the stomach bacterial community compositions, diversity, and interactions in two common pika (Ochotona sp.) species in China, including Plateau pikas (Ochotona curzoniae) and Daurian pikas (Ochotona daurica) living in the Qinghai-Tibet Plateau and the Inner Mongolia Grassland, respectively. The bacterial communities can be divided into two distinct phylogenetic clusters. The most dominant bacteria in cluster I were unclassified bacteria. Cluster II was more diverse, predominantly consisting of Bacteroidetes, followed by unclassified bacteria, Firmicutes and Proteobacteria. Three dominant genera (Prevotella, Oscillospira, and Ruminococcus) in pika stomachs were significantly enriched in cluster II. In addition, seasons, host species, and sampling sites as well as body weight and sex had no significant impacts on the composition and diversity of pika stomach communities. Interestingly, Plateau pikas harbored a more complex bacterial network than Daurian pikas, and these two pika species showed different co-occurrence patterns. These results suggested that the pika stomach harbors a diverse but relatively stable and unique bacterial community, which is independent on host (host species, body weight, and sex) and measured environmental factors (sampling sites and seasons). Interestingly, host species shapes the microbial interactions rather than diversity of stomach bacterial communities in pikas, reflecting specific niche adaptation of stomach bacterial communities through species interactions.

Methane oxidation driven by aerobic methanotrophs plays a critical role in the alleviation of global warming. Yet, we still know little about the assembly mechanisms of methanotrophic communities and the corresponding drivers in mountain soils. Here, we comprehensively investigated methanotrophic bacteria along an elevational gradient (1800–4100 m) in Mount Gongga, China. Our results indicated that previously unrecognized AOB-rel methanotrophs predominated in mountain forest soils, and they showed distinct phylogenetic differentiation and pH preferences (pH 5.9–7.2 and pH 4.7–5.6 for AOB-rel subclade 1 and 2, respectively). Soil pH, temperature and precipitation primarily shaped methanotrophic communities. The community assembly of aerobic methanotrophs was governed mainly by deterministic processes. Our findings also implied that more acidic soils contained less phylogenetically clustered methanotrophic communities, and more neutral soils harbored more phylogenetically clustered communities. This study is the first to illustrate the significant role of soil pH in the assembly of aerobic methanotrophic communities and reinforce the importance of AOB-rel methanotrophs in atmospheric methane oxidation process in mountain forest soils.

The biogeographical distribution of methanotrophic communities and the mechanisms driving methanotrophic community assembly in grassland soils are largely unknown. In this study, the assembly mechanisms of methanotrophic communities and the niche preferences of specific methanotrophic taxa were investigated in three Chinese grassland regions, including the Inner Mongolian Plateau (IMP), the Xinjiang Autonomous Region (XAR) and the Tibetan Plateau (TP) across 1500, 1000 and 1000 km, respectively. We analyzed the relative importance of deterministic and stochastic processes on methanotrophic community assembly and assessed how assembly is affected by environmental and spatial factors. The results revealed the presence of various methanotrophic taxa in the different grassland regions. Deterministic processes were dominant in the methanotrophic community assembly, and heterogeneous selection had a greater contribution in shifting the methanotrophic community than did homogeneous selection, dispersal limitations, homogenizing dispersal and drift. Moreover, key environmental factors shaping the methanotrophic communities were scale-dependent and varied among the three regions. The primary variables identified as shaping methanotrophic communities were the aridity index, total nitrogen, and mean annual temperature in the IMP, XAR and TP grasslands at regional scales, whereas pH was the primary variable when considering all of the regions together. In general, the soil methanotrophic community assembly was primarily influenced by deterministic processes and responded in a predictable manner to major environmental factors at a regional scale.

In this study, the soils with or without earthworms (Eisenia fetida) were treated with one of the two following nitrification inhibitors (NIs): dicyandiamide (DCD) or 3,4-dimethylpyrazole phosphate (DMPP); then, the soils were incubated for 90 days in laboratory mesocosms. The cumulative nitrous oxide (N2O) emission increased from 74.08 μg N2O-N kg−1 in the control to 384.69 μg N2O-N kg−1 in the earthworm-treated soil. The addition of NI decreased the cumulative N2O emissions from soils by 67.1 % in the DCD treatment and 73.4 % in the DMPP treatment without earthworms and by 79.0 and 81.0 % with earthworms, respectively. After 90 days, the richness of nirK gene in the soil decreased in both DCD and DMPP treatments compared with control, and the abundance of denitrifying bacteria in the gut of earthworm declined to less than 1/1000 or 1/100 of those without NIs. At 7 and 90 days, N2O production by denitrification in earthworm gut homogenates in both NI treatments decreased compared to those without NIs. Therefore, this study provided a fundamental evidence for that the application of NI-mitigated N2O emission induced by earthworm (E. fetida).

A laboratory study was conducted to determine the effect of 3,4-dimethylpyrazole phosphate (DMPP) and dicyan diamide (DCD) on nitrous oxide (N 2 O) emission, mineral nitrogen (NH 4 + -N, NO 3 – -N) contents, as well as ammonia oxidizing and denitrifying microbes in a greenhouse vegetable soil. Five treatments were established at 55% and 75% water filled pore space (WFPS): no fertilizer; urea; urea + manure (UM); urea + manure + DCD (UMDCD) and urea + manure + DMPP (UMDMPP). The application rate of urea and manure was 1800 kg N/ha and 1000 kg N/ha, respectively. DMPP and DCD were applied at the rate of 0.5% and 2% of urea-N application rate, respectively. Compared to UMDCD treatment, UMDMPP treatment significantly reduced N 2 O emission and NO 3 -N content and delayed ammonia oxidation, and showed a stronger inhibition effect on ammonium-oxidizing bacteria at both WFPS. Moreover, the copy numbers of nirS and nirK genes decreased significantly in the presence of DMPP at both WFPS, but were not affected by DCD. These results suggest that the application of DMPP is more effective than DCD on N 2 O mitigation in high N level vegetable soil, although the application rate of DMPP was one quarter that of DCD.

Temperate steppe is extremely sensitive to the current global changes. However, what are the main environmental variables driving microbial diversity in temperate steppe are still unclear, something that impairs doing predictions about the expected effects of global changes on microbe-mediated ecological functions. This is why, in this study, the relationship between soil microbial diversity and environmental variables in Chinese temperate steppe is investigated. In this study, significant correlations between soil bacterial α-diversity and mean annual precipitation and the aridity index were observed at the whole region scale. No clear correlations between microbial α-diversities and other measured environmental variables were found at the whole temperate steppe region and sub-regions. On the other hand, β-diversity was strongly related to spatial variables and climate variables for bacteria, while spatial variables and soil organic matters were more related with fungal β-diversity. In addition, the mean annual temperature was highly correlated with microbial β-diversity at different spatial scales, suggesting that it could be a good single predictor of soil microbial assemblage in temperate steppe. β-Diversities are more explained by combined effect of local environmental variables based on variation partitioning analysis, reflecting the community assemblage is more likely driven by species sorting through environmental filtering.

Assembly mechanisms and responses of diazotrophic habitat specialists, opportunists, and generalists may differ among various steppe ecosystems. In this study, we investigated the ecological processes that determine the assemblies of diazotrophic communities in meadows and typical steppes (MT), desert steppes (D), and sandy steppes (S) and the effects of habitat environments on diazotrophic specialists, opportunists, and generalists in Inner Mongolia, China. The results showed that taxonomic and phylogenetic communities of diazotrophs were clustered according to their habitat types, as community dissimilarities among habitat types were significantly higher than those within them. Variable selection and dispersal limitation were recognized as the dominant ecological processes that shape diazotrophic community assemblages. Furthermore, the diazotrophic populations were dichotomized into specialists, opportunists and generalists with various strategies to adapt to habitat types. The richness of specialists significantly correlated with vegetation variables, implying that specialists have greater responses to vegetation than generalists and opportunists. This study provides insights into the mechanisms of diazotrophic community differentiation when habitat environments change.

Nitrous oxide (N2O) emissions from agricultural soils, mainly caused by chemical nitrogen (N) fertilizer inputs, are major sources of N2O in Chinese terrestrial ecosystems. Thus, attempts to reduce N2O emissions from agricultural soils by optimizing N applications are receiving increasing attention. Further, organic fertilizers are being increasingly used in China to improve crop production/quality and prevent or reduce soil degradation. However, organic and chemical fertilizers are often both applied in spring in northeast China, which promotes N2O emissions and may be sub-optimal. Therefore, we hypothesized that reducing applications of chemical fertilizer N and applying manure in autumn could be an effective strategy for mitigating N2O emissions from cropped soils in the region. To test this hypothesis, we established a field trial to investigate the effects of different combinations of chemical N fertilizer applications and animal manure in autumn on both N2O emissions and maize (Zea mays L.)...