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In the process of biological carbon (C) sequestration during reforestation in degraded red soil, due to the decomposition of soil microorganisms, the interaction between soil organic carbon (SOC) and aggregates has an important effect on soil C sequestration. In this study, six common reforestation models and three soil layers were selected in a degraded red soil area of the central subtropical region to determine the composition of soil aggregates and the distribution of SOC in soil aggregates. Based on the results of the soil physicochemical properties and microbial community composition biomass, we assessed the changes in aggregate-associated organic C storage during fluctuations in the stability of the aggregates. After reforestation, the SOC stock increased by 131.28–140.00%. Compared with the three pure forests and broad-leaved mixed forests, coniferous and broad-leaved mixed forests showed the largest proportion of macroaggregates (85.48–89.37%) and higher SOC accumulation. Soil microbial biomass mainly affected the decomposition process of SOC by affecting the stability of the soil aggregates, and the effect of bacteria was more significant. Coniferous and broad-leaved mixed forests can provide more soil microorganisms and C sources than pure forest, thus promoting macroaggregate formation and stability and related organic C storage. This reforestation model has greater C sequestration potential. [ABSTRACT FROM AUTHOR]

Summary: Nitrogen (N) enrichment poses threats to biodiversity and ecosystem stability, while arbuscular mycorrhizal (AM) fungi play important roles in ecosystem stability and functioning. However, the ecological impacts, especially thresholds of N enrichment potentially causing AM fungal community shifts have not been adequately characterized.Based on a long‐term field experiment with nine N addition levels ranging from 0 to 50 g N m−2 yr−1 in a temperate grassland, we characterized the community response patterns of AM fungi to N enrichment.Arbuscular mycorrhizal fungal biomass continuously decreased with increasing N addition levels. However, AM fungal diversity did not significantly change below 20 g N m−2 yr−1, but dramatically decreased at higher N levels, which drove the AM fungal community to a potentially unstable state. Structural equation modeling showed that the decline in AM fungal biomass could be well explained by soil acidification, whereas key driving factors for AM fungal diversity shifted from soil nitrogen : phosphorus (N : P) ratio to soil pH with increasing N levels.Different aspects of AM fungal communities (biomass, diversity and community composition) respond differently to increasing N addition levels. Thresholds for substantial community shifts in response to N enrichment in this grassland ecosystem are identified. [ABSTRACT FROM AUTHOR]

To feed the growing human population, natural grasslands are being converted to agricultural use at a massive scale. This conversion may have negative consequences for soil biodiversity, but its impact on the community assembly of differentially microbial groups remains largely unknown. Here, we investigated the diversity and community compositions of bacteria, archaea, fungi and protists, using a paired sampling of grassland and cropland soils across the agro‐pastoral ecotone of northern China. Land‐use conversion decreased α diversity of bacteria, fungi and protists, and altered the structures of the entire soil microbial community (archaea, bacteria, fungi and protists). The community assembly of archaea and bacteria was dominated by stochastic processes, and that of protists dominated by deterministic processes in both land‐use types. By contrast, the fungal community was governed more strongly by stochastic processes in grassland soil, than by deterministic processes in cropland soil. Our findings support the ʻsize‐plasticityʼ hypothesis that smaller body‐sized microorganisms (archaea and bacteria) are more structured by stochastic processes, and larger one (protist) is more influenced by deterministic processes. Our study demonstrates that distinct ecological processes govern microbial community assembly, and land‐use change regulates the balance between determinism and stochasticity. [ABSTRACT FROM AUTHOR]

Intensive greenhouse production involving excessive fertilizer and organic manure application rates may affect soil chemical and biological quality. Soil samples from 50 commercial greenhouses for tomato production in northern China were collected for the evaluation of the status of soil fertility and identification of the soil chemical factor that exerts the strongest influence on microbial functional diversity. The soil total nitrogen content showed high soil fertility and was 68% higher than 1000 mg kg−1 and 14% higher than 1500 mg kg−1. Differential soil pH values caused statistically significant shifts in microbial metabolic activity (average well color development, AWCD) and Shannon's diversity index using BiologTM ECO plates assay. The highest soil microbial functional diversity was observed at near neutral pH values. When individual data points were plotted against soil organic matter (SOM), significant positive associations with soil microbial biomass nitrogen and AWCD were observed. The canonical correspondence analysis confirmed that shifts in the soil microbial functional diversity were associated with changes in pH, total nitrogen, and SOM. This study indicated that excessive fertilization changed the community-level physiological profile of the soil microorganisms, and this effect can be a consequence of changes in soil pH under intensive greenhouse management. [ABSTRACT FROM AUTHOR]

Purpose: A field experiment was conducted to assess the role of nitrogen (N) and water addition in shaping soil fungal communities and co-occurrence networks in temperate grassland, northern China. Materials and methods: We measured soil fungal and plant community compositions, and also soil properties including available N, phosphorus, potassium concentrations, soil pH, and soil moisture. Soil fungal co-occurrence networks were constructed using a random matrix theory–based network inference approach. Results and discussion: Plant species richness was decreased by N addition but increased by water addition, whereas fungal richness was decreased by N addition. The fungal community composition was significantly changed by both N addition and water addition. Soil fungal α diversity and β diversity were explained by a combination of variations in plant species richness and plant functional composition, and also by changes in soil pH via the soil acidification pathway induced by N and water addition. The fungal co-occurrence networks were more complex and clustered under water addition than that in ambient precipitation. Conclusions: Our results suggested that plant functional composition, plant species richness, and soil acidification should be incorporated into ecosystem models for predicting soil fungal communities under future climate changes in terrestrial ecosystems. [ABSTRACT FROM AUTHOR]

Microplastics are emerging pollutants that can adsorb heavy metals and threaten human health through food chain. Recently, there has been increasing interest in understanding the adsorption behavior of heavy metals by microplastics in farmland soil. In particular, arsenic (As), as a carcinogen, has the potential to be adsorbed by soil microplastics. However, the mechanisms and controlling factors of As adsorption by microplastics in farmland soil under natural conditions are still unknown. Here, microplastics and As were respectively added to farmland soils with different physicochemical properties from twelve provinces of China for adsorption experiment. We performed surface analysis of microplastics, quantified As accumulation through quasi-first-order kinetic equation and developed regression models to screen the factors controlling As adsorption. The results showed that the adsorption of As by soil microplastics was a chemical process accompanied by the loss of electrons from oxygen-containing functional groups. Soil cation exchange capacity (CEC) was the main factor controlling the adsorption rate, while soil organic matter (SOM), total nitrogen (TN) and CEC mainly influenced the equilibrium adsorption capacity. This is the first report on microplastic-As adsorption in natural soil, which allows deeper insights into risk assessment, prediction and control of microplastic-As pollution in agricultural soil. [Display omitted] • As was captured by the oxygen on the soil microplastic surface after adsorption. • The rate of As adsorption by soil microplastics was mainly controlled by CEC. • The equilibrium adsorption capacity of As was affected by CEC, TN and SOM. [ABSTRACT FROM AUTHOR]

We performed a landscape-scale investigation to compare the arbuscular mycorrhizal fungal ( AMF) communities between grasslands and farmlands in the farming-pastoral ecotone of northern China., AMF richness and community composition were examined with 454 pyrosequencing. Structural equation modelling ( SEM) and multivariate analyses were applied to disentangle the direct and indirect effects (mediated by multiple environmental factors) of land use on AMF., Land use conversion from grassland to farmland significantly reduced AMF richness and extraradical hyphal length density, and these land use types also differed significantly in AMF community composition. SEM showed that the effects of land use on AMF richness and hyphal length density in soil were primarily mediated by available phosphorus and soil structural quality. Soil texture was the strongest predictor of AMF community composition. Soil carbon, nitrogen and soil pH were also significantly correlated with AMF community composition, indicating that these abiotic variables could be responsible for some of the community composition differences among sites., Our study shows that land use has a partly predictable effect on AMF communities across this ecologically relevant area of China, and indicates that high soil phosphorus concentrations and poor soil structure are particularly detrimental to AMF in this fragile ecosystem. [ABSTRACT FROM AUTHOR]

Arbuscular mycorrhizal (AM) fungi are ubiquitous symbionts of higher plants in terrestrial ecosystems, while the occurrence of the AM symbiosis is influenced by a complex set of abiotic and biotic factors. To reveal the regional distribution pattern of AM fungi as driven by multiple environmental factors, and to understand the ecological importance of AM fungi in natural ecosystems, we conducted a field investigation on AM fungal abundance along environmental gradients in the arid and semi-arid grasslands of northern China. In addition to plant parameters recorded in situ, soil samples were collected, and soil chemo-physical and biological parameters were measured in the lab. Statistical analyses were performed to reveal the relative contribution of climatic, edaphic and vegetation factors to AM fungal abundance, especially for extraradical hyphal length density (HLD) in the soil. The results indicated that HLD were positively correlated with mean annual temperature (MAT), soil clay content and soil pH, but negatively correlated with both soil organic carbon (SOC) and soil available N. The multiple regressions and structural equation model showed that MAT was the key positive contributor and soil fertility was the key negative contributor to HLD. Furthermore, both the intraradical AM colonization (IMC) and relative abundance of AM fungi, which was quantified by real-time PCR assay, tended to decrease along the increasing SOC content. With regard to the obvious negative correlation between MAT and SOC in the research area, the positive correlation between MAT and HLD implied that AM fungi could potentially mitigate soil carbon losses especially in infertile soils under global warming. However, direct evidence from long-term experiments is still expected to support the AM fungal contribution to soil carbon pools. [ABSTRACT FROM AUTHOR]

Large amounts of nitrogen (N) are loaded in tropical and subtropical regions due to anthropogenic activities. However, the long-term effect of this deposition on soil biodiversity and its ecological functions remains poorly understood. In this study, we established a 10-year-long field experiment examining the effect of simulated N deposition on soil bacterial diversity and litter decomposition processes in a subtropical Chinese fir forest. The N levels were 0 (control), 6, 12, and 24 g m−2 yr−1. Soil bacterial diversity was measured by high throughput sequencing analysis, while litter decomposition was investigated by a microcosm experiment with a reciprocal soil and litter design. Our long-term experimental results demonstrated that N addition significantly changed soil pH, NH 4 +-N, available P and soil moisture; reduced soil bacterial diversity; and changed soil microbial community composition at the phyla and class levels. Meanwhile, the rate of litter decomposition decreased in treatments with high doses of N addition. The decreased soil pH and changes in understory plants were significantly correlated with the altered soil microbial diversity and community composition according to the structure equation model analysis. Our results showed that changes in soil microbial community composition (but not soil microbial diversity) mainly contributed to the decline in litter decomposition in higher doses of N addition. Our findings conclude that global change phenomena such as N deposition would depress both above- and below-ground biodiversity and would strongly affect ecosystem functions and processes in subtropical forests. • A 10-year N addition experiment was conducted in a subtropical forest of China. • Soil microbial diversity/community and their litter decomposition function were investigated. • N addition decreased soil microbial diversity and changed community composition. • Changes in soil microbial community composition are correlated to the decreased rate of litter decomposition. [ABSTRACT FROM AUTHOR]

In the permafrost region of northeastern China, vegetation and soil environment have showed response to permafrost degradation triggered by global warming, but the corresponding variation of the soil microbial communities remains poorly investigated. Here, a field investigation in the continuous permafrost region was conducted to collect 63 soil samples from 21 sites along a latitudinal gradient to assess the distribution pattern of microbial communities and their correlation with environmental factors. High-throughput Illumina sequencing revealed that bacterial communities were dominated by Proteobacteria, Acidobacteria, Bacteroidetes and Actinobacteria. Both microbial richness and phylogenetic diversity decreased initially and then increased as the latitude increased. UniFrac analysis of microbial communities detected significant differences among latitudes. Variation partitioning analysis and structural equation models revealed that environmental variables, including geographic factors, plant-community factors and soil physicochemical factors, all played non-negligible roles in affecting the microbial community structures directly or indirectly. Redundancy analysis and boosted regression tree analysis further highlighted the influences of soil pH and plant richness on microbial community compositions and diversity patterns. Taken together, these results suggest that the distribution pattern of soil microbial communities shows distinct changes along the latitudinal gradients in northeastern China and is predominantly mediated by soil pH and plant diversity.