Gradient In Grasslands Research Articles

Holocene Neolithic human activity shaped ecosystem functions through the altering of vegetation traits in Zhejiang, eastern China

Since the Holocene, long–term human activities have altered the composition, structure, and function of ecosystems, yet uncertainty remains regarding the underlying mechanism of a variety of vegetation responses to both natural and anthropogenic forces. In this study, we collected and categorized 37 fossil pollen records from Zhejiang, a region characterized by continuous Neolithic Cultures in eastern China, into natural and human–impacted sites. The aim was to reconstruct past long–term changes in plant traits and to investigate variations in ecosystem functioning under the pressure of natural climate shifts and anthropogenic disturbances. Our findings reveal that, during the Holocene, plant functional traits at natural sites gradually adapted to warmer and wetter conditions, with the natural functional dispersion (FDis) showing a steady decrease between 9.0 and 4.0 cal ka BP. At human–impacted sites, intensified human activities gradually transformed the landscape from forest to grassland and shrubland, allowing light–demanding vegetation to thrive due to extended canopy gaps. Pioneer plants flourished in the secondary succession, leading communities to exhibit more aggressive resource acquisition strategies compared to a natural community. With the progression of agriculture towards intensive practices, ancestors might have expanded their original ecological niches by shaping a landscape encompassing a gradient of grasslands, shrublands, and forests, leading to an increase in plant diversity and a reversal in the trend of decreasing FDis. Higher functional diversity is considered a potential factor in maintaining ecosystem stability. Neolithic human activities, by modifying plant composition, community structure, and shaping landscape gradients, probably contributed to enhancing the stability of past terrestrial ecosystems.

Habitat Selection of Three Neotropical Grassland Birds Is Dependent on Vegetation Structure and Resources

Grassland birds are globally imperiled. Those of endemic Neotropical savannas may be particularly threatened as knowledge of the ecology of many species is lacking, restricting our ability to take decisive conservation action. During the dry (non-breeding) season of 2010, we studied the population size, distribution, and habitat associations of the Cock-tailed Tyrant (Alectrurus tricolor), Black-masked Finch (Coryphaspiza melanotis), and Wedge-tailed Grass-finch (Emberiziodes herbicola) across a disturbance-mediated savanna–grassland gradient in Beni, Bolivia. We used distance sampling and surveyed structural and resource-specific habitat features at plots where birds were present versus random locations. Occupancy models identified fine-scale habitat associations. Cock-tailed Tyrant (7.1 ind./km2) specialized on open habitats in areas expected to be heavily inundated in the wet season, avoided trees, and selected tall grassy swards. Black-masked Finch (25.1 ind./km2) occurred across the gradient, associating with tall, forb-rich swards, sparse shrubs, and low levels of fruiting and seeding vegetation. Wedge-tailed Grass-finch (27.9 ind./km2) also occurred across the gradient, particularly associated with tall, forb-rich swards, abundant seeding grasses, and sparse shrubs. Our results offer the first quantitative abundance estimates for these species in Beni, provide vital baselines for future monitoring, and improve knowledge of the ecology and conservation management needs of these species. Importantly, our results suggest that populations of these three grassland birds may be best maintained in heterogenous, mosaic landscapes that can be produced by carefully managed burning and grazing. Further research in the breeding season would facilitate making stronger, more specific management recommendations.

Manganese and soil organic carbon stability on a Hawaiian grassland rainfall gradient

Manganese (Mn) is a possibly critical yet poorly understood element controlling soil carbon (C) stocks. In temperate forests, Mn availability correlates strongly with organic C decay, but we know little about its role in soil organic matter decomposition in most terrestrial environments. In this study, we evaluate Mn in grassland C dynamics along a rainfall gradient in Hawaii. We measured Mn, organic matter, and microbial enzyme activities along the rainfall gradient to evaluate relationships among Mn oxidation state, chemical/biological reactivity, and soil C turnover. Neither Mn abundance nor its oxidation state are strong predictors of organic C instability along the grassland gradient. We also used an incubation experiment to investigate how dissolved organic C and CO2 release from the grassland soil respond to increased Mn bioavailability. We found that Mn availability did not correlate with soil C instability; Mn additions corresponded with lower dissolved organic C and CO2 fluxes from soils than did additions of deionized water. Mn availability may not predict soil C stability as well as previously thought.

Characteristics and Driving Factors of Precipitation-Use Efficiency across Diverse Grasslands in Chinese Loess Plateau

Understanding the characteristics of the precipitation-use efficiency (PUE) of grassland ecosystems and its drivers is critical for predicting how ecosystem functions will respond to future climate change. In this study, we investigated several covarying biotic and abiotic factors (e.g., biomass, coverage, diversity, precipitation, temperature, and humid index (HI)) of 81 sites across a broad natural grassland gradient in the Loess Plateau of China to determine how PUE changes along a precipitation gradient and to assess the effects of biotic and abiotic factors on PUE. Our results showed that HI, below-ground biomass (BGB), vegetation coverage, and species diversity were the most important biotic factors in controlling PUE. HI had a higher positive indirect effect on PUE mainly through its influence on community characteristics. Our results suggest that precipitation and community characteristics are both important for the precipitation-use efficiency of natural grasslands across the arid and semiarid areas of the Loess Plateau. Additionally, improving the vegetation structure and increasing species diversity can help enhance the adaptability of grassland ecosystems to climate change.

Belowground plant traits and their ecosystem functions along aridity gradients in grasslands

Ecosystem responses to environmental change are usually studied solely using aboveground (usually leaf) traits. However, belowground plant traits, such as fine roots and coarse belowground organs, likely play a crucial role in ecosystem response, especially under aridifcation. We conducted a literature survey on belowground plant traits along aridity gradients in temperate grasslands to propose which effect traits might be connected with abrupt vegetation changes that would occur with aridification due to environmental change. With increasing aridity, seasonal regeneration decreasingly relies on recruitment from the belowground bud bank and increasingly relies on regeneration from seeds. This leads to greater inter-annual variability in biomass production. Other belowground traits, such as bud bearing organs and fine root distribution in the soil, also shifts along the aridity gradient. As aridifcation begins, we propose that plants would become more conservative in their belowground traits producing lower amounts of belowground litter. Increasing aridifcation would lead to the loss of rhizomatous plants from the community and a prevalence of deep rooting plants leading to changes in soil resource utilization and increasing susceptibility to soil erosion. Under extreme aridification, perennial plants, except those with bulbs, would be lost from the community and replaced by annuals which produce low amounts of litter and use only ephemeral water resources in the upper soil layers. Belowground plant traits, such as belowground clonal growth organs, bud banks, and fine root distributions, may provide a more mechanistic understanding behind shifts in ecosystem functioning due to environmental change.

Will the grass be greener on the other side of climate change? (with corrigendum)

Increasing atmospheric [CO2] is stimulating photosynthesis and plant production, increasing the demand for nitrogen relative to soil supply with declining global foliar nitrogen concentrations as a consequence. The effects of such oligotrophication on the forage quality of sweetveld, mixed veld, and sourveld grasslands in South Africa, which support livestock production and native ungulates, are unknown. Soil characteristics and the herbage quality of an abundant grass are described from baseline historical (mid- 1980s) data collected across a sweet-mixed-sour grassland gradient in KwaZulu-Natal. Sourveld occurred on the most acidic, dystrophic soils and exhibited a pronounced decline in leaf nitrogen, digestibility, and other macronutrients during winter, in sharp contrast to sweetveld, on nutrient-rich soils, where forage quality varied little seasonally. In a carbon-enriched, warmer, and most likely drier future climate, we predict that forage quality will not be substantially altered in sweetveld where soil nutrients and temperature are not limiting but that sourveld could become ‘sourer’ because soil nutrients will be inadequate to match higher plant production promoted by elevated [CO2] and warmer and longer growing seasons. Reassessing historical data and seasonal and spatial monitoring of forage quality will enable assessment of past and future impacts of climate change on grassland forage quality. Significance: Grassland forage quality will likely decline with elevated [CO2] and warming, particularly in sourveld. Climate change could deepen and widen the sourveld winter forage bottleneck, necessitating greater supplementary feeding of livestock.

Smaller, more diverse and on the way to the top: Rapid community shifts of montane wild bees within an extraordinary hot decade

AbstractAimGlobal warming is assumed to restructure mountain insect communities in space and time. Theory and observations along climate gradients predict that insect abundance and richness, especially of small‐bodied species, will increase with increasing temperature. However, the specific responses of single species to rising temperatures, such as spatial range shifts, also alter communities, calling for intensive monitoring of real‐world communities over time.LocationGerman Alps and pre‐alpine forests in south‐east Germany.MethodsWe empirically examined the temporal and spatial change in wild bee communities and its drivers along two largely well‐protected elevational gradients (alpine grassland vs. pre‐alpine forest), each sampled twice within the last decade.ResultsWe detected clear abundance‐based upward shifts in bee communities, particularly in cold‐adapted bumble bee species, demonstrating the speed with which mobile organisms can respond to climatic changes. Mean annual temperature was identified as the main driver of species richness in both regions. Accordingly, and in large overlap with expectations under climate warming, we detected an increase in bee richness and abundance, and an increase in small‐bodied species in low‐ and mid‐elevations along the grassland gradient. Community responses in the pre‐alpine forest gradient were only partly consistent with community responses in alpine grasslands.Main ConclusionIn well‐protected temperate mountain regions, small‐bodied bees may initially profit from warming temperatures, by getting more abundant and diverse. Less severe warming, and differences in habitat openness along the forested gradient, however, might moderate species responses. Our study further highlights the utility of standardized abundance data for revealing rapid changes in bee communities over only one decade.

Climatic controls on stable carbon and nitrogen isotope compositions of temperate grasslands in northern China

The natural abundances of stable carbon (C) and nitrogen (N) isotopes (δ13C and δ15N) are extensively used to indicate the C and N biogeochemical cycles at large spatial scales. However, the spatial patterns of δ13C and δ15N in plant-soil systems of grasslands in northern China and their main driving factors across regional climatic gradient are still not well understood. We measured plant and soil δ13C and δ15N compositions as well as their associated environmental factors across 2000 km climatic gradient (-0.2 to 9 °C; 152 to 502 mm) in grasslands of northern China. The soil δ13C and δ15N values in surface were lower than those in bottom for temperate typical steppe but had no significant differences for temperate meadow steppe and temperate desert steppe. Soil δ13C values declined with increasing soil organic carbon (SOC) but increased as mean annual temperature (MAT). These changes were attributed to the microbial decomposition rate. The δ15N values in soil and plant were negatively correlated with MAT and mean annual precipitation (MAP), which were mainly related to the low soil organic matter mineralization rate and the shift of dominant species from C4 to C3. Our results indicate the spatial patterns and different influencing factors on δ13C and δ15N values along the climatic gradient in grasslands of northern China. The findings will provide scientific references for future research on the C and N biogeochemical cycles of temperate grasslands.

Hydrothermal conditions determine soil potential net N mineralization rates in arid and semi‐arid grasslands

Abstract Soil net nitrogen (N) mineralization is a key biogeochemical process influencing plant available N and net primary productivity in terrestrial ecosystems. However, the spatial variations and controlling factors of soil net N mineralization (RPNM) in arid and semi‐arid grasslands are less studied and unclear. In this study, we investigated the soil RPNM by performing a laboratory incubation experiment. Soil samples were collected from 30 sites in three east–west transects on the Inner Mongolia Plateau (MP), Loess Plateau (LP) and Tibetan Plateau (TP) along a 3200 km arid and semi‐arid grassland gradient, with each transect containing three different grassland types (meadow steppe [MS], typical steppe [TS] and desert steppe [DS], respectively). Results showed that the average RPNM values ranged from −0.37 to 1.29 mg N kg−1 day−1, with a significantly lower RPNM found in the DS (0.08 ± 0.01 mg N kg−1 day−1) compared with those in the MS (0.30 ± 0.03 mg N kg−1 day−1) and in the TS (0.33 ± 0.03 mg N kg−1 day−1) in the MP and LP transects (p < 0.05). This difference could be explained by variations in climatic and soil factors, such as hydrothermal index (HT), the soil pH, soil organic matter (SOM) and precipitation. However, no significant differences in RPNM were found among different grassland types in the TP transect, possibly due to the similarly low microbial activity, as indicated by the microbial biomass carbon values. Across all three grassland transects, HT, SOM and microbial variables were the major factors controlling RPNM, which together explained 20.7% of the variation in RPNM. Further structural equation model analysis indicated HT was an integral predictor of RPNM, directly or indirectly via SOM, under different conditions of precipitation and temperature. Our findings provide field evidence and parameters for biogeochemical cycling to better predict future N transformation processes under changing precipitation and temperature regimes across a wide range of arid and semi‐arid grassland ecosystems. Read the free Plain Language Summary for this article on the Journal blog.

Biomassza-fajgazdagság kapcsolatok vizsgálata szikes gyepekben és vizes élőhelyeken

For an effective conservation and management in grasslands and wetlands it is essential to understand mechanisms sustaining biodiversity. Understanding biomass-species richness relationships is in the focus of recent scientific interest both from the agricultural and nature conservation point of view. We provided a detailed analysis of the relationship between major biomass components (total aboveground biomass and litter), and species richness along a long productivity gradient in grasslands and wetlands. We studied eight types of alkali and loess grasslands and five types of alkali wetlands in Hortobágy National Park, East-Hungary. We found that the relationship between total biomass and species richness can be described by humped-back curves both in grasslands and wetlands. was valid for the relation of total biomass and species richness. We detected the maximum of species richness at total biomass scores of 750 g/m2 in grasslands and at 2000 g/m2 in wetlands. Our results suggest that litter is one of the major factors controlling species richness in highly productive grasslands and wetlands.

The relationship of δD and δ18O in surface soil water and its implications for soil evaporation along grass transects of Tibet, Loess, and Inner Mongolia Plateau

Soil evaporation plays an important role in non-productive water loss and local climate regulation. The deviation of the relationship between δD and δ18O in surface soil water from that in precipitation is used to indicate the integrative results of the soil evaporation process, but the distinction between the slope of the soil water evaporation line (SEL) and line-conditioned excess (lc-excess) as individual indicators has not been identified. Furthermore, spatial variability and interaction effects of climate, soil, and vegetation on soil evaporation in arid and semi-arid grasslands remain poorly understood. We established 3 west-to-east sampling transects along with increasing precipitation and decreasing aridity index gradients in grasslands of the Tibetan (TP, 1500 km), Loess (LP, 600 km), and Inner Mongolia (MP, 1200 km) Plateaus. Slope of SEL and weighted mean lc-excess were calculated according to the δD and δ18O in soil water, which was extracted from soils collected at 10 cm intervals to a depth of 1 m along with soil profiles during the vigorous growing season. We found that lc-excess appeared relatively more robust than slope in representing soil evaporation process because lc-excess was determined by evaporation fractionation factors and soil residual water storage, while slope was regulated only by evaporation fractionation factors. Soil evaporation, as indicated by lc-excess, exhibited decreasing trends from west to east, and was controlled by relative humidity in TP, and by vegetation coverage in LP and MP. Our results highlighted that the soil evaporation process may be more sensitive to climate change in TP, and vegetation restoration in LP and MP.

Changes in plant-herbivore network structure and robustness along land-use intensity gradients in grasslands and forests.

Land-use intensification poses major threats to biodiversity, such as to insect herbivore communities. The stability of these communities depends on interactions linking herbivores and host plants. How interaction network structure begets robustness, and thus stability, in different ecosystems and how network structure and robustness are altered along land-use intensity gradients are unclear. We analyzed plant-herbivore networks based on literature-derived interactions and long-term sampling from 289 grasslands and forests in three regions of Germany. Network size and nestedness were the most important determinants of network robustness in both ecosystems. Along land-use intensity gradients, networks in moderately grazed grasslands were more robust than in those managed by frequent mowing or fertilization. In forests, changes of network robustness along land-use intensity gradients relied on changes in plant species richness. Our results expand our knowledge of the stability of plant-herbivore networks and indicate options for management aimed at stabilizing herbivore communities.

Alkalinity gradients in grasslands alter soil bacterial community composition and function

AbstractClarifying the bacterial community composition and function in alkali soils is pivotal to the soil capability of sustaining venerable ecosystems. Using MiSeq sequencing, PICRUSt, and Biolog (https://www.biolog.com), we investigated the bacterial community composition and metabolic function of microbes in three soils differing in the severity of alkalinity. A high level of alkalinity deceased the diversity of microbial community and altered microbial community composition with the increase in relative abundances of 21 genera. The linear discriminate analysis and effect size analysis found most of 54 biomarkers belonged to Actinobacteria and Proteobacteria. Redundancy analysis indicated that the succession of bacterial community and metabolic characteristics of microbes were highly affected by the nutrient availability and soil moisture. The utilization rates of carbohydrates, amino acids, carboxylic acids, polymers, phenolic compound, and aminesides by microbes were positively correlated with soil nutrient concentrations but negatively correlated with the exchangeable sodium percentage and pH. Severe alkalinity inhibited the microbial community diversity and function on carbohydrate metabolisms.

Ant species but not trait diversity increases at the edges: insights from a micro‐scale gradient in a semi‐natural Mediterranean ecosystem

1. Different habitat types are generally associated with shifts in ant species and traits, and even along a micro‐scale woodland–grassland gradient, ant biodiversity may change at the edge proximities as a result of abiotic alterations. However, to the best of authors' knowledge, the changes in ant diversity along this type of gradient are understudied, especially from a functional perspective.2. The authors sampled ant species in eight micro‐scale woodland–grassland gradients in a Mediterranean ecosystem, each comprising 16 m, to assess how ant species diversity, community composition, functional structure, and single‐ and multi‐trait functional diversity change at the edge and in the two adjacent habitats (woodland and grassland) as the distance from the edge increases.3. No differences in species richness, species diversity, and community composition were found within the woodland and grassland habitats. Distance from the edge into the adjacent habitats explained changes in functional structure and diversity, which mainly increased in the grassland habitat; body length, leg length, sugar‐based diet, dominant behaviour, and multi‐trait diversity increased in the grassland. Along the micro‐scale gradient, edges showed the highest species diversity and community composition that resulted from the overlap of the communities from the adjacent habitats.4. This study shed light on changes in ant species and traits along a micro‐scale woodland–grassland gradient, and it highlights the importance of integrating different diversity approaches (functional and taxonomic) at a micro‐spatial scale.

Storage of soil phytoliths and phytolith-occluded carbon along a precipitation gradient in grasslands of northern China

Climatic factors including mean annual precipitation (MAP) significantly influence the carbon (C) cycle in terrestrial ecosystems and Earth overall. Phytolith-occluded carbon (PhytOC) is an important C sequestration mechanism and as such plays a vital role in global long-term C sequestration. Understanding the spatial variability in the storage of soil phytoliths and PhytOC and its relationship with climate is critical for evaluating the impact of global climate change on terrestrial ecosystem functions. However, little is known about the responses of soil phytoliths and PhytOC to MAP in grassland ecosystems. This study sampled soil from 24 natural, semi-arid steppe sites along a 2,500 km transect with a precipitation gradient of 243–481 mm yr−1 in northern China. We investigated the influence of precipitation on the spatial distributions of soil phytoliths and PhytOC storage. Storage of soil phytoliths in bulk soil (0–100 cm depth) ranged from 21.3 ± 0.4 to 88.4 ± 20.3 t ha−1 along the precipitation gradient. Amounts of soil phytoliths and PhytOC storage were significantly and positively correlated with MAP. Multiple regression analysis revealed that phytolith storage in bulk soil was best predicted by MAP (R = 0.5) and soil organic carbon (SOC, R = 0.4), with these two variables accounting for about 58% of the total variation observed. Considering the forecasted increase in MAP in the Inner Mongolian steppe due to climate change, and the strong influence of MAP on the annual net primary productivity (ANPP) and related soil PhytOC input from litter decomposition in this region, we expect that ecosystem primary productivity will increase from deserts to meadow steppe and thereby promote soil PhytOC storage. These findings have important implications for understanding the dynamics of soil phytoliths, and predicting the impacts of global climate change on ecosystem functions and management practices in the East Asian steppe ecosystems.

Do the Quality and Quantity of Honey Bee-Collected Pollen Vary Across an Agricultural Land-Use Gradient?

Pollen is the source of protein for most bee species, yet the quality and quantity of pollen is variable across landscapes and growing seasons. Understanding the role of landscapes in providing nutritious forage to bees is important for pollinator health, particularly in areas undergoing significant land-use change such as in the Northern Great Plains (NGP) region of the United States where grasslands are being converted to row crops. We investigated how the quality and quantity of pollen collected by honey bees (Apis mellifera L. [Hymenoptera: Apidae]) changed with land use and across the growing season by sampling bee-collected pollen from apiaries in North Dakota, South Dakota, and Minnesota, USA, throughout the flowering season in 2015-2016. We quantified protein content and quantity of pollen to investigate how they varied temporally and across a land-use gradient of grasslands to row crops. Neither pollen weight nor crude protein content varied linearly across the land-use gradient; however, there were significant interactions between land use and sampling date across the season, particularly in grasslands. Generally, pollen protein peaked mid-July while pollen weight had two maxima in late-June and late-August. Results suggest that while land use itself may not correlate with the quality or quantity of pollen resources collected by honey bees among our study apiaries, the nutritional landscape of the NGP is seasonally dynamic, especially in certain land covers, and may impose seasonal resource limitations for both managed and native bee species. Furthermore, results indicate periods of qualitative and quantitative pollen dearth may not coincide.

Limited evidence for spatial resource partitioning across temperate grassland biodiversity experiments.

Locally, plant species richness supports many ecosystem functions. Yet, the mechanisms driving these often-positive biodiversity-ecosystem functioning relationships are not well understood. Spatial resource partitioning across vertical resource gradients is one of the main hypothesized causes for enhanced ecosystem functioning in more biodiverse grasslands. Spatial resource partitioning occurs if species differ in where they acquire resources and can happen both above- and belowground. However, studies investigating spatial resource partitioning in grasslands provide inconsistent evidence. We present the results of a meta-analysis of 21 data sets from experimental species-richness gradients in grasslands. We test the hypothesis that increasing spatial resource partitioning along vertical resource gradients enhances ecosystem functioning in diverse grassland plant communities above- and belowground. To test this hypothesis, we asked three questions. (1) Does species richness enhance biomass production or community resource uptake across sites? (2) Is there evidence of spatial resource partitioning as indicated by resource tracer uptake and biomass allocation above- and belowground? (3) Is evidence of spatial resource partitioning correlated with increased biomass production or community resource uptake? Although plant species richness enhanced community nitrogen and potassium uptake and biomass production above- and belowground, we found that plant communities did not meet our criteria for spatial resource partitioning, though they did invest in significantly more aboveground biomass in higher canopy layers in mixture relative to monoculture. Furthermore, the extent of spatial resource partitioning across studies was not positively correlated with either biomass production or community resource uptake. Our results suggest that spatial resource partitioning across vertical resource gradients alone does not offer a general explanation for enhanced ecosystem functioning in more diverse temperate grasslands.

Plant Identity Influences Foliar Fungal Symbionts More Than Elevation in the Colorado Rocky Mountains.

Despite colonizing nearly every plant on Earth, foliar fungal symbionts have received little attention in studies on the biogeography of host-associated microbes. Evidence from regional scale studies suggests that foliar fungal symbiont distributions are influenced both by plant hosts and environmental variation in climate and soil resources. However, previous surveys have focused on either one plant host across an environmental gradient or one gradient and multiple plant hosts, making it difficult to disentangle the influence of host identity from the influence of the environment on foliar endophyte communities. We used a culture-based approach to survey fungal symbiont composition in the leaves of nine C3 grass species along replicated elevation gradients in grasslands of the Colorado Rocky Mountains. In these ecosystems, the taxonomic richness and composition of foliar fungal symbionts were mostly structured by the taxonomic identity of the plant host rather than by variation in climate. Plant traits related to size (height and leaf length) were the best predictors of foliar fungal symbiont composition and diversity, and composition did not vary predictably with plant evolutionary history. The largest plants had the most diverse and distinctive fungal communities. These results suggest that across the ~ 300m elevation range that we sampled, foliar fungal symbionts may indirectly experience climate change by tracking the shifting distributions of plant hosts rather than tracking climate directly.

Archaea and bacteria respectively dominate nitrification in lightly and heavily grazed soil in a grassland system

To investigate the effects of stocking rates on nitrification activity and active nitrifying communities in a typical steppe grazing system, we conducted a laboratory incubation study using soil from a 10-year-old grassland gradient grazing experiment with sheep. A combination of molecular methods, such as DNA-based stable-isotope probing (DNA-SIP), real-time quantitative PCR, and high-throughput sequencing, was used to identify changes of nitrification activity and active nitrifying communities under different stocking rates (0 (SR0), 3 (SR3), 6 (SR6), and 9 (SR9) sheep per ha). The nitrification activity of soils was significantly increased by light grazing (SR3), while it was significantly decreased by heavy grazing (SR9). Nitrososphaera viennensis lineage of ammonia-oxidizing archaea (AOA) functionally predominated over ammonia-oxidizing bacteria (AOB) in nitrification in the SR3 soil, while the Nitrosospira cluster 3 of AOB was the major player in the SR9 soil. Therefore, stocking rates altered the distribution of active nitrifying communities by affecting soil chemical and physical conditions.

Carbon and nitrogen allocation shifts in plants and soils along aridity and fertility gradients in grasslands of China.

Plant carbon (C) and nitrogen (N) stoichiometry play an important role in the maintenance of ecosystem structure and function. To decipher the influence of changing environment on plant C and N stoichiometry at the subcontinental scale, we studied the shoot and root C and N stoichiometry in two widely distributed and dominant genera along a 2,200‐km climatic gradient in China's grasslands. Relationships between C and N concentrations and soil climatic variables factors were studied. In contrast to previous theory, plant C concentration and C:N ratios in both shoots and roots increased with increasing soil fertility and decreased with increasing aridity. Relative N allocation shifted from soils to plants and from roots to shoots with increasing aridity. Changes in the C:N ratio were associated with changes in N concentration. Dynamics of plant C concentration and C:N ratios were mainly caused by biomass reallocation and a nutrient dilution effect in the plant‐soil system. Our results suggest that the shifted allocation of C and N to different ecosystem compartments under a changing environment may change the overall use of these elements by the plant‐soil system.