Grasslands In China Research Articles

Thaumarchaeota affiliated with Soil Crenarchaeotic Group are prevalent in the alkaline soil of an alpine grassland in northwestern China

Thaumarchaeota are key players within the global nitrogen cycle. Investigations of the Thaumarchaeota communities are important for an integrated understanding of nitrogen nutrient cycle in soil ecosystems. Therefore, the objective of this study was to examine the presence and diversity of Thaumarchaeota within an alkaline soil in the Bayinbuluke alpine grassland, China. The community DNAs were directly extracted from soil samples, collected on 15 July 2014, and paired-end V5–V6 amplicons of the 16S rRNA gene were sequenced by Illumina Miseq. Sequencing reads were processed using the Quantitative Insights Into Microbial Ecology (QIIME) v. 1.8.0 pipeline. After quality control, the validated sequence reads were classified into different operational taxonomic units (OTUs) based on a 97% identity level, using the Uclust algorithm to generate stable OTUs. The longest sequence in each cluster was chosen to be the representative sequence, and sequences were annotated using the Silva rRNA database project. In the analyzed grassland soil, Thaumarchaeota had a relative abundance of 3.65 to 51.07% of the microbial community (mean = 20.20%), representing the most dominant phylum. The thaumarchaeal community was dominated by the Soil Crenarchaeotic Group (SCG, 34.55 to 99.82%, mean = 95.10%), with specifically low fraction of the ammonia-oxidizing genus Candidatus Nitrososphaera (2.83 to 30.37%, mean = 13.10%) and remaining unclassified genus. Our results show Thaumarchaeota affiliated with SCG were prevalent in the alkaline soil of this grassland.

Yaks and sheep trigger different changes in the grasshopper assemblages of the Qilian Mountains via differentially altering plant assemblages

1. The Qilian Mountains represent one of the key livestock‐raising grasslands in China. The two main herbivore species raised in this area – yaks and sheep – are of critical economical value. Grasshoppers compete with these animals for available nutrients, creating multifaceted relationships between livestock, grasshoppers and plants. A clear understanding of such relationships is lacking and is urgently needed to guide conservation efforts.2. This study aims to document the effects of yak and sheep grazing on grasshopper assemblages and to elucidate the underlying mechanisms of such effects.3. It is shown here that yaks and sheep impact grasshopper assemblages differently. Grasshopper assemblages exhibited lower density, biodiversity, richness, and evenness of distribution in yak‐grazed pastures than in grazing‐free grasslands. Sheep‐grazed pastures exhibited a dramatically divergent picture, with elevated density, biodiversity and richness, and a slightly decreased evenness of distribution. Grasshoppers were generally larger in grazed pastures than in grazing‐free grasslands, especially in yak‐grazed plots.4. The present study suggests that differences between yak and sheep pastures in plant assemblage structure and plant traits are probably the underlying forces driving the differences in grasshopper assemblage structure and grasshopper traits, respectively.5. The study shows that the grasshopper habitat indicator species differ between yak and sheep pastures, raising the possibility that such indicators can be used to monitor grassland usage and degradation in the Qilian Mountains.6. These results provide novel insights into the dynamic interactions of common domesticated herbivore species, grasshoppers and plants in Qilian Mountains, which augment current knowledge and may ultimately lead to better conservation practices.

Carbon availability affects soil respiration response to drying-rewetting cycles in semiarid grasslands of China under nitrogen deposition

Soil carbon (C) availability is an important limiting factor affecting the magnitude of soil respiration with increasing the drying-rewetting cycle number. Previous studies have reported that because of a deficiency in available C, improved nitrogen (N) availability has no effects on soil respiration in semiarid grasslands. However, it is not well understood whether the effects of N availability on soil respiration in response to drying-rewetting cycles is regulated by C availability in semiarid grasslands under N deposition scenarios. A field experiment was conducted in a semiarid grassland of northern China to investigate the response of soil CO2 efflux to drying-rewetting cycles (natural precipitation events) with the addition of labile C (glucose, 48 g C m−2 a−1) and N (NH4NO3, 10 g N m−2 a−1) in August 2014. The drying-rewetting cycle significantly increased soil respiration rate in the treatments with both C and N additions, whereas it did not significantly increase soil respiration rate in the treatments with added N alone. After the first drying-rewetting cycle, a significant increase in soil microbial biomass C (MBC) content was observed in the treatments with both C and N additions but was not observed in the treatment with added N alone. After a series of drying-rewetting cycles, the cumulative CO2 efflux over the observed period was significantly higher in the treatments with both C and N additions than that in the treatment with added N alone. These findings imply that improved N availability during the period of 20 days has no effects on soil respiration in response to the drying-rewetting cycle due to microbial C limitation under N deposition scenarios in a semiarid grassland.

Effects of fairy ring fungi on plants and soil in the alpine and temperate grasslands of China

Soil fungi are considered to be key regulators of plant and soil relationships. The fairy rings (FRs) caused by basidiomycete fungi can influence plant productivity and soil nutrient and microbiome composition. We sought to explore the role of FRs in plant communities and soil properties for two types of grasslands in China. Plant and soil samples were collected from three concentric zones: outside the ring (OUT), on the ring (ON), and inside the ring (IN). Data were collected on plant productivity, plant diversity, soil properties, and soil bacterial diversity. We found that FRs significantly improved plant productivity and diversity in both alpine and temperate grasslands. In the alpine grassland, soil water content, pH and bacterial diversity were lower in the ON zone compared to the OUT zone. Likewise, in temperate grasslands, water content was lower in the ON zone compared to both OUT and IN zones. Also, soil pH and bacterial diversity were higher on the ON zone compared to other both zones. Based on our data, we believe that FR fungi increase plant productivity and diversity, and change the composition of soil bacterial species and diversity. We suggest that the effects of FR fungi on plants included the increase of the soil nutrient content and the effects of FR fungi on soil bacteria included the changes in soil water content and pH value.

Changes in productivity and carbon storage of grasslands in China under future global warming scenarios of 1.5°C and 2°C

Abstract Aims The impacts of future global warming of 1.5°C and 2°C on the productivity and carbon (C) storage of grasslands in China are not clear yet, although grasslands in China support ~45 million agricultural populations and more than 238 million livestock populations, and are sensitive to global warming. Methods This study used a process-based terrestrial ecosystem model named ORCHIDEE to simulate C cycle of alpine meadows and temperate grasslands in China. This model was driven by high-resolution (0.5° × 0.5°) climate of global specific warming levels (SWL) of 1.5°C and 2°C (warmer than pre-industrial level), which is downscaled by EC-EARTH3-HR v3.1 with sea surface temperature and sea-ice concentration as boundary conditions from IPSL-CM5-LR (low spatial resolution, 2.5° × 1.5°) Earth system model (ESM). Important Findings Compared with baseline (1971–2005), the mean annual air temperature over Chinese grasslands increased by 2.5°C and 3.7°C under SWL1.5 and SWL2, respectively. The increase in temperature in the alpine meadow was higher than that in the temperate grassland under both SWL1.5 and SWL2. Precipitation was also shown an increasing trend under SWL2 over most of the Chinese grasslands. Strong increases in gross primary productivity (GPP) were simulated in the Chinese grasslands, and the mean annual GPP (GPPMA) increased by 19.32% and 43.62% under SWL1.5 and SWL2, respectively. The C storage increased by 0.64 Pg C and 1.37 Pg C under SWL1.5 and SWL2 for 50 years simulations. The GPPMA was 0.670.390.88 (0.82) (model meanminmax (this study)), 0.850.451.24 (0.97) and 0.940.611.30 (1.17) Pg C year−1 under baseline, SWL1.5 and SWL2 modeled by four CMIP5 ESMs (phase 5 of the Coupled Model Inter-comparison Project Earth System Models). In contrast, the mean annual net biome productivity was −18.55−40.374.47 (−3.61),18.65−2.0364.03 (10.29) and 24.158.3838.77 (24.93) Tg C year−1 under baseline, SWL1.5 and SWL2 modeled by the four CMIP5 ESMs. Our results indicated that the Chinese grasslands would have higher productivity than the baseline and can mitigate climate change through increased C sequestration under future global warming of 1.5°C and 2°C with the increase of precipitation and the global increase of atmospheric CO2 concentration.

Stability of Ecosystem CO2 Flux in Response to Changes in Precipitation in a Semiarid Grassland

Carbon dioxide (CO2) flux provides feedback between C cycling and the climatic system. There is considerable uncertainty regarding the direction and magnitude of the responses of this process to precipitation changes, hindering accurate prediction of C cycling in a changing world. We examined the responses of ecosystem CO2 flux to ambient precipitation and experimentally decreased (−35%) and increased precipitation (+20%) in a semiarid grassland in China between July 2013 and September 2015. The measured CO2 flux components included the gross ecosystem productivity (GEP), net ecosystem CO2 exchange (NEE), ecosystem respiration (Re), and soil respiration (Rs). The results showed that the seasonal and diurnal patterns of most components of ecosystem CO2 flux were minimally affected by precipitation treatments, with less than 4% changes averaged across the three growing seasons. GEP and NEE had a quadratic relationship, while Re and Rs increased exponentially with soil temperature. GEP, RE, and Rs, however, decreased with soil moisture. Decreased precipitation reduced the dependence of CO2 flux on soil temperature but partly increased the dependence on soil moisture; in contrast, increased precipitation had the opposite influence. Our results suggested a relatively stable CO2 flux in this semiarid grassland across the tested precipitation regimes.

Effects of species-dominated patches on soil organic carbon and total nitrogen storage in a degraded grassland in China.

BackgroundPatchy vegetation is a very common phenomenon due to long-term overgrazing in degraded steppe grasslands, which results in substantial uncertainty associated with soil carbon (C) and nitrogen (N) dynamics because of changes in the amount of litter accumulation and nutrition input into soil.MethodsWe investigated soil C and N stocks beneath three types of monodominant species patches according to community dominance. Stipa krylovii patches, Artemisia frigida patches, and Potentilla acaulis patches represent better to worse vegetation conditions in a grassland in northern China.ResultsThe results revealed that the soil C stock (0–40 cm) changed significantly, from 84.7 to 95.7 Mg ha−1, and that the soil organic carbon content (0–10 cm) and microbial biomass carbon (0–10 and 10–20 cm) varied remarkably among the different monodominant species communities (P < 0.05). However, soil total nitrogen and microbial biomass nitrogen showed no significant differences among different plant patches in the top 0–20 cm of topsoil. The soil C stocks under the P. acaulis and S. krylovii patches were greater than that under the A. frigida patch. Our study implies that accurate estimates of soil C and N storage in degenerated grassland require integrated analyses of the concurrent effects of differences in plant community composition.

Detecting Land Degradation in Eastern China Grasslands with Time Series Segmentation and Residual Trend analysis (TSS-RESTREND) and GIMMS NDVI3g Data

Grassland ecosystems in China have experienced degradation caused by natural processes and human activities. Time series segmentation and residual trend analysis (TSS-RESTREND) was applied to grasslands in eastern China. TSS-RESTREND is an extended version of the residual trend (RESTREND) methodology. It considers breakpoint detection to identify pixels with abrupt ecosystem changes which violate the assumptions of RESTREND. With TSS-RESTREND, in Xilingol (111°59′–120°00′E and 42°32′–46°41′E) and Hulunbuir (115°30′–122°E and 47°10′–51°23′N) grassland, 6% and 3% of the area experienced a decrease in greenness between 1984 and 2009, 80% and 73% had no significant change, 5% and 3% increased in greenness, and 9% and 21% were undetermined, respectively. RESTREND may underestimate the greening trend in Xilingol, but both TSS-RESTREND and RESTREND revealed no significant differences in Hulunbuir. The proposed TSS-RESTREND methodology captured both the time and magnitude of vegetation changes.

Effects of grazing patterns on grassland biomass and soil environments in China: A meta-analysis.

BackgroundGrazing has important influences on the structures and functions of grassland ecosystems, but the effects of grazing patterns on grassland biomass and soil environments in China remain unclear.ObjectiveWe employed a meta-analysis to identify the response of biomass and soil environments to different grazing patterns in China.MethodsPeer-reviewed journal articles were searched using the Web of Science and China National Knowledge to compile a database. A total of 1011 sets of sample observations satisfied the sampling standards; these were derived from 140 study sites and were obtained from 86 published articles. We conducted random effects meta-analyses and calculated correlation coefficients with corresponding 95% confidence intervals.ResultsGrazing significantly decreased the total biomass, aboveground biomass (AGB), belowground biomass (BGB), soil organic matter, soil total nitrogen, soil total phosphorus and soil water content but increased the root-to-shoot ratio, soil available nitrogen, soil pH and bulk density. Generally, increasing grazing intensity and duration significantly increased the effects of grazing on the biomass and soil environment. Additionally, the smallest effects of grazing on the biomass and soil environments were observed under light grazing and cattle grazing alone. Moreover, non-growing season grazing significantly increased AGB, while annual grazing and growing-season grazing significantly reduced AGB. Furthermore, AGB was positively correlated with soil organic matter, soil available phosphorus and bulk density, while BGB was negatively correlated with pH.ConclusionsThese findings highlight the importance of grazing patterns in the biomass and soil environment response to grazing and suggest that cattle grazing alone and grazing during the non-growing season are beneficial for improving the quality of grassland in China.

Metabolic response and correlations between ions and metabolites in Phragmites communis under long-term salinity toxicity

Phragmites communis has a long history in Songnen grassland of China and has a series of biological, ecological as well as genetic characteristics contributing to its adaptation to the specific local climatic and edaphic conditions. The aim of the present study was to investigate the ions balance and their relationship to metabolites in P. communis under three salinity stress conditions. Results showed that the contents of Na+, Cl−, and SO42− significantly increased in P. communis leaves, while K+, Mg2+, and Mn2+ decreased. Moreover, Na+ and Cl− had significant negative correlations with metabolites involved in the tricarboxylic acid cycle (TCA cycle), and significant positive correlations with glycolysis. The metabolite results showed that high contents of sugars and proline played important roles in developing salinity tolerance, indicating that glycolysis and proline biosynthesis were enhanced; however, this consumes large amounts of energy and likely caused the TCA cycle to be inhibited. The results suggested that P. communis might enhance its salinity tolerance mainly through increased glycolysis and energy consumption. In addition, restricting Na+ accumulation and increasing of Cl−, and rearrangement of metabolite production in P. communis tissues are possible causes of salinity tolerance. Therefore, salinity caused systems alterations in widespread metabolic networks involving TCA cycle, glycolysis and proline biosynthesis. These findings provided new insights for the P. communis metabolic adaptation to salinity and demonstrated the ions balance and metabolites in P. communis are possibly attributable to development of salinity tolerance.

Reply to the comment on “Effects of grazing exclusion on carbon sequestration in China's grassland”

How to understand the interactive influence of environmental changes on the total grasshopper density (TGD) becomes an urgent issue in grassland ecosystems. Large-scale studies are ideal for assessing the relative contributions of multiple factors on grasshopper community dynamics. Using data from 634 sites, linkages of community habitats (plant functional groups (PFGs), vegetative litter (VT) and soil types (ST)) and grasshopper occurrence were studied in a farming-pastoral zone across Inner Mongolia. Each of the three primary grassland ecosystem drivers influenced total grasshopper density. The absence of VT (VTabsence) can decrease the total grasshopper density by degrading the habitat conditions. Similarly, grasshopper communities prefer to feed on legumes and forbs rather than grasses due to the plant-trait variance in PFGs. Moreover, total grasshopper density was driven by complex interactions, caused by PFGs, soil types and vegetation litter. Our results improve the understanding of where grasshoppers might occur and provide helpful strategies to prevent the outbreak of grasshoppers.

Did a meta-analysis accurately estimate the temporal trends of carbon stock change after grazing exclusion in China's grasslands? A comment on “Effects of grazing exclusion on carbon sequestration in China's grassland,” by

The temporal pattern of carbon stock changes in response to grazing exclusion (GE) is important for grassland ecosystem restoration policy. The carbon stock change rate is the quotient computed by dividing the change in carbon stock after GE by GE duration. We modeled varying carbon stock change rates with GE durations based on data from a meta-analysis by Deng et al. (2017). We found that the close relationship between the carbon stock change rate and GE duration was mostly driven by GE duration in the denominator, rather than by carbon stock changes in the numerator. We argue that Deng et al.'s conclusion that the exponential decay trend varies with GE duration was inaccurate and that it was misleading to suggest there is a temporal pattern to carbon stock changes that is associated with GE duration. Their model may further encourage GE-based policy that includes fencing as a major practice of grassland restoration. However, this practice yields clearly negative impacts on herders' livelihoods, animal husbandry, pastoral social development and wildlife protection.

Rating the Degradation of Natural Hay Pastures in Northern China

Natural hay pastures in semi-arid pastoral areas produce the highest yields of hay in northern China. However, long-term continuous hay harvesting with no rest interval has resulted in severe degradation across widespread areas of these natural hay pastures. In addition, no clear data exist on the spatial distribution or degree of degradation occurring in natural hay pastures primarily because a nationally unified and normative evaluation standard is lacking. In view of the above problems, we employed an analytic hierarchy process to carry out screening and accuracy validation of evaluation indicators for natural hay pastures in north China grasslands (temperate meadow steppes, temperate steppes, mountain meadows, and lowland meadows). Our study identified seven easily measured indicators that reflect the state of natural hay pastures (average height, aboveground biomass, coverage, proportion of medium grasses, litter biomass, proportion of degradation-indicative plants, and proportion of bare spots and saline-alkali spots). A five-level scoring method was employed to delineate the threshold range for these indicators, The results of this study show that this method effectively solved the technical bottleneck for graded evaluation of degradation in natural hay pastures. This provides a theoretical basis for the scientific assessment of natural hay pasture degradation as well as important technical support for sustainable use of natural hay pastures and livestock production.

Spatial, temporal, and spectral variations in albedo due to vegetation changes in China’s grasslands

Changes in Earth’s albedo due to vegetation dynamics, snow cover, and land cover change have attracted much attention. However, the effects of vegetation dynamics on albedo have not been comprehensively documented according to its spatial (regional), temporal (within growing season), and spectral (visible, near-infrared, and shortwave) characteristics. This study examined the effects of vegetation greenness on albedo from 2000 to 2014 in China’s grasslands, which have considerable intra- and inter-annual variations, using remote sensing-based albedo and two-band Enhanced Vegetation Index (EVI2) data. Generally, we found an insignificant negative correlation between the shortwave (SW) albedo and EVI2 for grasslands in China. However, the visible (VIS) albedo was more sensitive to changes in vegetation greenness than near-infrared (NIR) albedo in China’s grasslands. The relationship between the NIR albedo and EVI2 was more complicated, especially in the Tibetan Plateau (TP), where the correlation was negative in the early growing season and positive in the late growing season; while the correlation between the NIR albedo and EVI2 was always negative in main part of Inner Mongolia (IM). The different albedo-EVI2 relationships in IM and TP may be related to differences in soil albedos. The higher sensitivity of the SW albedo to vegetation greenness change in IM, the stronger effect on land surface radiation budget. Our finding about vegetation-induced changes in albedo differ in space, time and spectral bands is expected to contribute to the improvement of land surface models.

Producing a Distant Centre: The role of wilderness in the post-Mao Tibetan Buddhist revival

AbstractThis article addresses how wilderness—through its qualities of remoteness and wildness—plays an essential role in the production of a vital religious centre in Tibet. By drawing on in-depth ethnographic observations in Yachen Gar, a mega-sized Buddhist encampment in the nomadic grasslands of China's northwestern Sichuan province, I examine the spatial and material features of the encampment, how various agents utilize these features to produce specific relations with it, and how, in this process, Yachen has become a centre of the Buddhist revival in Kham Tibet. I will present three ethnographic accounts—which focus on a Tibetan nun from the Tibet Autonomous Region (TAR), Chinese pilgrims, and reactions to the spread of electricity in Yachen—to address the ways in which Yachen is emplaced within the spatial and material tensions implemented and imagined by different participants. These accounts ultimately show how materiality plays a crucial role in forging the various contesting relations, actions, and meanings that constitute a social space.

Distribution of lignin phenols in comparison with plant-derived lipids in the alpine versus temperate grassland soils

As a major plant-derived soil organic carbon (SOC) component, lignin-derived phenolic compounds show varying biogeochemical characteristics compared to plant-derived lipid moieties. Comparing their distribution patterns can provide information on mechanisms governing SOC preservation and dynamics. However, the large-scale distribution pattern and stability of lignin versus plant-derived lipids are still poorly constrained. Here we investigated the distribution of lignin phenols versus plant-derived lipids in the surface soils across the alpine versus temperate grasslands of China and Mongolia. Lignin phenols were isolated by cupric oxide oxidation method and compared with the previously analyzed plant-derived lipids (cutin and suberin). A comprehensive list of environmental variables was compiled to disentangle the climatic, edaphic and vegetation influences on lignin phenols’ distribution in the soil. Lignin phenols showed similar SOC-normalized concentrations in the alpine and temperate grassland soils despite a higher plant input to the latter, suggesting better lignin preservation in the cold region. However, compared with plant-derived lipids (cutin and suberin), lignin seems to be less stabilized. The variation of lipid versus lignin components is mainly related to climate (particularly aridity) in the alpine grassland soils, while the relative abundance of plant lipids and lignin phenols is more related to reactive mineral contents in the temperate grassland soils. Lignin contributes differentially to SOC accumulation in the alpine and temperate soils: while lignin seems to be better preserved in the cold region, lignin phenols decrease relative to other carbon components with SOC accrual in the temperate region. Overall, lignin distribution and fate may be more sensitive to carbon source variations than temperature shifts in the grasslands.

Effects of different fencing regimes on community structure of degraded desert grasslands on Mu Us desert, China.

Grazing is one of the major anthropogenic driving factors influencing community structure and ecological function of grasslands. Fencing has been proved to be one of the main measures for rehabilitating degraded grasslands in northwestern China. However, data from combined empirical studies on the effects of different management regimes in desert grasslands are lacking. So we selected long‐term fencing (fenced since 1991), mid‐term fencing and seasonal fencing (fenced since 2002), and adjacent free‐grazing grasslands to investigate vegetation and soil properties on southwest Mu Us desert. Our results showed that fencing increased plant cover, height, aboveground biomass (AGB) of different plant life‐form groups, Shannon–Wiener diversity index, Evenness index, Simpson index, total soil nitrogen, total soil phosphorus, and soil organic matter, but decreased plant density, species richness, Richness index, soil bulk density, water content, and pH. However, 22–24 years of long‐term complete fencing might cause redegradation of vegetation and soil nutrients, characterized by the reduction of some vegetation properties, biodiversity, total AGB, and some soil properties. Seasonal fencing with 11–13 year was more beneficial to vegetation restoration than that with completely fencing measures. Our study suggests that appropriate artificial disturbances, such as seasonal fencing (winter grazing and summer fencing), should be used after long‐term fencing in order to maintain grassland productivity and biodiversity. These findings will help to provide theoretical support for vegetation restoration and sustainable management in grassland under grazing prohibition at Mu Us desert.

Nitrogen addition interacted with salinity-alkalinity to modify plant diversity, microbial PLFAs and soil coupled elements: A 5-year experiment

Atmospheric nitrogen (N) deposition has greatly increased in the past 50 years due to fossil fuel combustion and the use of synthetic fertilizers. Because N is the limiting nutrient for plant growth in terrestrial ecosystems, atmospheric deposition of N has the potential to increase biomass production, reduce species richness, inhibit microbial growth, and result in soil acidification. However, few studies have evaluated whether and how N inputs affect plant species diversity and the interactions among soil elements in saline-alkaline grassland ecosystems. The Songnen grassland of China is characterized by heterogeneous patches of saline-alkaline soils. A 5-year nitrogen deposition experiment was conducted in two contrasting saline-alkaline communities. Results showed that increasing N input increased the plant biomass production and reduced plant species richness in the low saline-alkaline stress community, but salinity-alkalinity was able to alleviate the negative effects of nitrogen input on community diversity. Plant communities were more sensitive to N addition than microbial communities. N addition induced a shift from N to P as the limiting factor in temperate grassland ecosystems. In particular, salinity-alkalinity in the high stress community increased the conversion rate from N to P limitation. These results highlight the importance of the integrative study of the plant-soil-microbe system in ecosystems under global N enrichment. Our study emphasizes the need for future research to understand the mechanisms that control biogeochemical cycling and maintain ecosystem stability under the combined conditions of N addition and other stress factors, such as saline-alkalinity.

Shrub encroachment increases soil carbon and nitrogen stocks in temperate grasslands in China

AbstractShrub encroachment has significant impacts on carbon (C) and nitrogen (N) dynamics of grassland ecosystems, but, how it influences soil organic C (SOC) and soil total N (STN) stocks of grasslands is not well documented, especially in deep soils. Here, we examined these effects by investigating the SOC density (SOCD) and the STN density (STND) at depths of up to 5 m in shrub patches and grassy matrix at 18 grassland sites in Inner Mongolia, China. Our results revealed that 44.0–54.1% of SOC and 65.5–74.8% of STN were stored in soil layers of 100 cm to 500 cm, and that shrub encroachment resulted in a significant accumulation of SOC and STN in shrub patches. The mean SOCD at 0–500 cm soil layers in shrub patches and grassy matrix was 11.34 and 8.39 kg C m−2, respectively, and the mean STND was 2.45 and 2.13 kg N m−2, respectively. These differences between the shrub patches and grassy matrix were equivalent to an increase in the mean SOC and STN stocks of 2.95 kg C m−2 and 0.32 kg N m−2, respectively. Increases in SOCD and STND mainly occurred in 30–300 cm soil layers, and varied between typical grassland and desert grassland. The changes in SOCD and STND exhibited significant negative correlations with temperature and pH and positive correlations with precipitation and plant biomass. Our findings suggest that shrub encroachment can significantly accumulate SOC and STN in deep soils in temperate grasslands, which helps to understand soil C and N dynamics in shrub‐encroached grasslands.

Urea fertilization decreases soil bacterial diversity, but improves microbial biomass, respiration, and N-cycling potential in a semiarid grassland

In this study, changes in plant diversity and aboveground biomass, soil chemical properties, microbial biomass and respiration, microbial composition, and microbial N-cycling potential (represented by the abundance of genes involved in N reaction) were studied after 3 years of urea fertilization (0, 25, 50, and 100 kg N ha−1 year−1) in a semiarid grassland in China. The microbial composition and N-cycling genes were determined using metagenome sequencing. Urea fertilization significantly decreased soil bacterial diversity, possibly through its negative effect on plant diversity, whereas it increased fungal diversity, and microbial biomass and respiration through enhancing aboveground biomass production with increases in the C input into the soil. However, above the threshold N rate of 50 kg N ha−1 year−1, microbial biomass and respiration decreased probably because of a strong N inhibitory effect on aboveground biomass. Further, urea fertilization increased the gene abundances of narH, nrfA, nirB, and napA, which are involved in dissimilatory nitrate reduction, and those of nifH and nifD, involved in N2 fixation, gdh, involved in organic N decomposition, and glnA, involved in glutamine synthesis and ureC. These findings suggested that urea addition has a positive effect on N-turnover potential. Burkholderiales and Rhizobiales play an important role in soil N cycling. Changes in plant community (diversity and biomass) were responsible for the shift in microbial diversity, biomass, and respiration, whereas alterations in inorganic N levels (exchangeable NH4+ and NO3−) potentially affected microbial N cycling. Our results show that N-mediated environmental stresses can play an important role in microbial diversity and functions, which appear to be mediated largely by plant–soil interactions.