Northern China's Grasslands Research Articles

Interactive effects of grassland utilization and climatic factors govern the plant diversity-soil C relationship in steppe of North China

The relationship between plant diversity and the ecosystem carbon pool is important for understanding the role of biodiversity in regulating ecosystem functions. However, it is not clear how the relationship between plant diversity and soil carbon content changes under different grassland use patterns. In a 3-year study from 2013 to 2015, we investigated plant diversity and soil total carbon (TC) content of grasslands in northern China under different grassland utilization methods (grazing, mowing, and enclosure) and climatic conditions. Shannon-Wiener and Species richness index of grassland were significantly decreased by grazing and mowing. Plant diversity was positively correlated with annual precipitation (AP) and negatively correlated with annual mean temperature (AMT). AP was the primary regulator of plant diversity. Grazing and mowing decreased TC levels in grasslands compared with enclosures, especially in topsoil (0–20 cm). The average TC content was decreased by 58 % and 36 % in the 0–10 cm soil layer, while it was decreased by 68 % and 39 % in 10–20 cm soil layer. TC was positively correlated with AP and negatively correlated with AMT. Principal component analysis (PCA) showed that plant diversity was positively correlated with soil TC, and the correlation decreased with an increase in the soil depth. Overall, this study provides a theoretical basis for predicting soil carbon storage in grasslands under human disturbances and climate change impacts.

Species’ geographical range, environmental range and traits lead to specimen collection preference of dominant plant species of grasslands in Northern China

Many different factors, such as species traits, socio-economic factors, geographical and environmental factors, can lead to specimen collection preference. This study aims to determine whether grassland specimen collection in China is preferred by species traits (i.e., plant height, flowering and fruiting period), environmental range (i.e., the temperature and precipitation range) and geographical range (i.e., distribution range and altitudinal range). Ordinary least squares models and phylogenetic generalized linear mixed models were used to analyze the relationships between specimen number and the explanatory variables. Random Forest models were then used to find the most parsimonious multivariate model. The results showed that interannual variation in specimen number between 1900 and 2020 was considerable. Specimen number of these species in southeast China was notably lower than that in northwest China. Environmental range and geographical range of species had significant positive correlations with specimen number. In addition, there were relatively weak but significant associations between specimen number and species trait (i.e., plant height and flowering and fruiting period). Random Forest models indicated that distribution range was the most important variable, followed by flowering and fruiting period, and altitudinal range. These findings suggest that future floristic surveys should pay more attention to species with small geographical range, narrow environmental range, short plant height, and short flowering and fruiting period. The correction of specimen collection preference will also make the results of species distribution model, species evolution and other works based on specimen data more accurate.

Grazing exclusion jeopardizes plant biodiversity effect but enhances dryness effect on multifunctionality in arid grasslands

Grassland biodiversity is vital for the provision of multiple ecosystem functions, termed ecosystem multifunctionality. As an effective practice of grassland management, grazing exclusion is widely used to restore the ecosystem multifunctionality of degraded grasslands, but it might not be always beneficial for conserving grassland biodiversity. Moreover, when grazing is excluded, it remains unknown whether grassland biodiversity promotes multifunctionality. Here, we conducted a field experiment of grazing exclusion along a gradient of climatic aridity across four major grassland types in the arid grasslands of northern China. We determined the effects of grazing exclusion on biodiversity and multifunctionality, and further investigated how grazing exclusion could modify biodiversity-multifunctionality relationships. We found that grazing exclusion increased soil fungal diversity, but had negligible effects on plant species richness and soil bacterial diversity. The effects of grazing exclusion on multifunctionality varied among grassland types: it promoted multifunctionality only in less arid grasslands. Importantly, multifunctionality was positively associated with plant species richness under grazing, but this positive association disappeared under grazing exclusion. In addition, we showed that climatic aridity affected multifunctionality indirectly through its negative effect on plant species richness under grazing, whereas such effect disappeared under grazing exclusion. Furthermore, aridity weakly reduced multifunctionality under grazing, and its negative effect was strengthened under grazing exclusion. Our results suggest that grazing exclusion restrains the capacity of plant biodiversity to sustain multiple ecosystem functions, and moreover, aggravates the negative influences of climatic dryness on ecosystem multifunctionality. Our findings illustrate the value of grazing for maintaining biodiversity-multifunctionality relationships and for mitigating the impacts of climate change in arid grasslands.

Nutrient resorption exacerbates nitrogen–phosphorus imbalances in plants under increasing nitrogen addition in a saline-alkaline grassland

Abstract Reabsorbing nutrients from senescent tissues before leaf falling has been recognized as a strategy to adapt to nutrient deficiency. However, how nutrient resorption modulates the nitrogen (N)–phosphorus (P) balance inside plants remains unclear, especially under increased soil N availability. We examined the impacts of N addition at varying rates (0–32 g N m−2 yr−1) on nutrient resorption and the performance of nutrient resorption on controlling the internal N–P balance in the leaf and stem of a dominant grass species, Leymus secalinus, in a saline-alkaline grassland in northern China. After 6 years of N addition, N concentration and N:P ratio in green and senesced tissues (leaf and stem) rose with increasing N addition. The P concentration in green tissues decreased, but did not significantly change in senesced tissues with increasing N addition. The N resorption efficiency (NRE), P resorption efficiency (PRE) and NRE:PRE ratio significantly decreased along the N addition gradient. Moreover, we found more sensitive responses of N:P ratio in senesced tissues than in green tissues; such exacerbation of plant internal N–P imbalances mainly resulted from a disproportionate reduction in nutrient resorption, especially NRE. Overall, our study suggested that differences in NRE and PRE further exacerbated the internal N–P imbalances in plant litters.

Effects of precipitation regime change and nitrogen deposition on soil nematode diversity in the grassland of northern China

Effects of precipitation regime change and nitrogen deposition on soil nematode diversity in the grassland of northern China

Similar effects of seasonal nitrogen enrichment on plant species–area relationship in a temperate grassland

1. Nitrogen (N) enrichment often decreases plant species richness in local communities, thus altering plant species–area relationships (SAR). However, whether N enrichment affects the SAR across global grasslands has not yet been well explored. Additionally, whether and how seasonal N enrichment alters the SAR remains unknown.2. This study employed data from global grasslands (meta-analysis) in combination with a seasonal field N addition experiment during the first 6 consecutive years (2014–2020) in a temperate grassland in northern China.3. We found that N addition did not alter the SAR slopes across global grasslands and our experimental grassland, but significantly reduced the intercepts (plant species richness at the 1 m2 plot scale). There was no significant difference among seasonal N treatments. The SAR intercepts were negatively correlated with increasing experimental years in our temperate grassland, without significant differences among the three seasonal N addition treatments, indicating a cumulative effect on the reduction in plant species richness at 1 m2 with N-enriched conditions.4. These results suggest that N enrichment affects the SAR in grassland ecosystems by reducing the SAR intercepts. Therefore, biodiversity conservation activities should be applied urgently in localities facing increasing atmospheric N deposition.

Spatial variations of fungal community assembly and soil enzyme activity in rhizosphere of zonal Stipa species in inner Mongolia grassland

Rhizosphere soil fungal and enzyme activities affect the nutrient cycling of terrestrial ecosystems, and rhizosphere fungi are also important participants in the ecological process of vegetation succession, responding to changes in plant communities. Stipa is an excellent forage grass with important ecological and economic value, and has the spatial distribution pattern of floristic geographical substitution. In order to systematically investigate the synergistic response strategies of fungal communities and enzyme activities in the rhizosphere under the vegetation succession. Here we explored the turnover and assembly mechanisms of Stipa rhizosphere fungal communities and the spatial variation of metabolic activity under the succession of seven Stipa communities in northern China grassland under large scale gradients. The results indicated that the composition, abundance and diversity of fungal communities and microbial enzyme activities in rhizosphere soil differed among different Stipa species and were strikingly varied along the Stipa community changes over the geographic gradient. As the geographical distribution of Stipa community changed from east to west in grassland transect, Mortierellomycetes tended to be gradually replaced by Dothideomycetes. The null models showed that the rhizosphere fungal communities were governed primarily by the dispersal limitation of stochastic assembly processes, which showed decreased relative importance from S. grandis to S. gobica. Moreover, the MAT and MAP were the most important factors influencing the changes in the fungal community (richness, β-diversity and composition) and fungal community assembly, while SC and NP also mediated fungal community assembly processes. These findings deepen our understanding of the responses of the microbial functions and fungal community assembly processes in the rhizosphere to vegetation succession.

Opposing responses of temporal stability of aboveground and belowground net primary productivity to water and nitrogen enrichment in a temperate grassland

AbstractChanges in water and nitrogen availability, as important elements of global environmental change, are known to affect the temporal stability of aboveground net primary productivity (ANPP). However, evidences for their effects on the temporal stability of belowground net primary productivity (BNPP), and whether such effects are consistent between belowground and aboveground, are rather scarce. Here, we investigated the responses of temporal stability of both ANPP and BNPP to water and nitrogen addition based on a 9‐year manipulative experiment in a temperate grassland in northern China. The results showed that the temporal stability of ANPP increased with water addition but decreased with nitrogen addition. By contrast, the temporal stability of BNPP decreased with water addition but increased with nitrogen enrichment. The temporal stability of ANPP was mainly determined by the soil moisture and inorganic nitrogen, which modulated species asynchrony, as well as by the stability of dominant species. On the other hand, the temporal stability of BNPP was mainly driven by the soil moisture and inorganic nitrogen that modulated ANPP of grasses, and by the direct effect of soil water availability. Our study provides the first evidence on the opposite responses of aboveground and belowground grassland temporal stability to increased water and nitrogen availability, highlighting the importance of considering both aboveground and belowground components of ecosystems for a more comprehensive understanding of their dynamics.

Growing-season drought and nitrogen addition interactively impair grassland ecosystem stability by reducing species diversity, asynchrony, and stability

Aboveground net primary productivity controls the amount of energy available to sustain all living organisms, and its sustainable provision relies on the stability of grassland ecosystems. Human activities leading to global changes, such as increased nitrogen (N) deposition and the more frequent occurrence of extreme precipitation events, with N addition increasing the sensitivity of ecosystem production stability to changes in the precipitation regime. However, whether N addition, in combination with seasonal precipitation increases or severe drought, affects ecosystem stability remains unclear. In this study, we conducted a six-year environmental change monitoring experiment in a semiarid grassland in northern China to test the effects of N addition, seasonal drought, and precipitation increases on the temporal stability of ecosystem productivity. Our study revealed that an interaction between drought and N addition reduced species diversity, species asynchrony, species stability, and thus ecosystem stability. These environmental change drivers (except for precipitation increase) induced a positive relationship between species asynchrony and diversity, whereas N addition interactively with drought and precipitation increase led to a negative relationship between diversity and species stability. Only N addition interactively with drought induced a positive species diversity–ecosystem stability relationship because lower species stability was overcome by increased species asynchrony. Our study is great importance to illustrate that production temporal stability tends to be inhibited with drought, though interactively with nutrient N addition. These findings highlight the primary role of asynchronous dynamics among species in modulating the effects of environmental change on diversity-stability relationships.

Temperate grassland vegetation restoration influenced by grazing exclusion and climate change

Grasslands are one of the most important terrestrial biomes, supporting a wide range of ecological functions and services. Grassland degradation due to overgrazing is a severe issue worldwide, especially in developing regions. However, observations from multiple sources have shown that temperate grasslands in China have significantly increased during the past two decades. It remains controversial what factors have driven the vegetation restoration in this region. In this study, we combined remote-sensing images and field survey datasets to quantify the contributions of different factors to vegetation restoration in six temperate grasslands in northern China. Across the six grasslands, the Normalized Difference Vegetation Index (NDVI) increased by 0.003–0.0319 year−1. The average contributions of grazing exclusion and climate change to the NDVI increase were 49.23 % and 50.77 %, respectively. Precipitation change was the primary climate factor driving vegetation restoration, contributing 50.76 % to the NDVI variance. By contrast, climate warming tended to slow vegetation restoration, and atmospheric CO2 concentration change contributed little to the NDVI increase in the temperate grasslands. These results emphasize the significant contributions of both climate change and human management to grassland vegetation restoration.

Root carbon and soil temperature may be key drivers of below-ground biomass in grassland following prescribed fires in autumn and spring

Under global warming, fire and the season in which the fire occurs both have important impacts on grassland plant biomass. Still, the effect of fire on below-ground biomass (BB) along a natural aridity gradient and the main impact factors remain unclear. Here, we conducted a fire manipulation experiment (including un-fired, autumn fire and spring fire treatments) to investigate the effects of prescribed fire on BB and its critical determinants along a transect of grassland in northern China. BB had different response strategies in different aridity regions and fire seasons, despite above-ground biomass (AB) and root-shoot ratio were not significantly affected by fire. General linear regression models revealed that the fire changed the trend of increasing BB to decreasing along increasing aridity (p ＜ 0.05). Random forest model (RFM) and partial correlations revealed that the BB was primarily influenced by aridity, followed by the nitrogen (N) and phosphorus (P) concentration ratio of AB under un-fired disturbance. For autumn fire, the BB was primarily influenced by below-ground biomass carbon concentration (BB c), followed by the C and N concentration ratio of BB. For spring fire, the BB was primarily influenced by soil temperature (ST), followed by aridity and soil total phosphorus concentration (Soil p). Furthermore, partial least squares path model (PLS-PM) revealed that autumn fires weakened the effects of environmental factors on BB, while spring fires enhanced the effects of soil nutrients on BB. These suggested that fire disrupted the original stable nutrient dynamics of BB. Our results suggested that fire promoted the growth of BB in relatively humid areas (aridity = 0.51–0.53) while inhibited the growth of BB in relatively arid areas (aridity = 0.68–0.74). BB c and ST may be key drivers of BB after prescribed fire in autumn and spring.

Altered Trends in Light Use Efficiency of Grassland Ecosystem in Northern China

Light use efficiency (LUE) is a crucial indicator used to reflect the ability of terrestrial ecosystems to transform light energy. Understanding the long-term trends in LUE and its influencing factors are essential for determining the future carbon sink and carbon sequestration potential of terrestrial ecosystems. However, the long-term interannual variability of LUE in grasslands in northern China at the ecosystem scale is poorly understood due to the limitations of the year length and the coverage of the site data. In this study, we assessed the long-term LUE trends in the grasslands of northern China from 1982 to 2018 and then revealed the relationships between interannual variability in LUE and climate factors. Our study showed a substantial rising trend for LUE from 1982 to 2018 in the grasslands of northern China (3.42 × 10−3 g C/MJ/yr). Regarding the different grassland types, alpine meadow had the highest growth rate (4.85 × 10−3 g C/MJ/yr), while temperate steppe had the lowest growth rate (1.58 × 10−3 g C/MJ/yr). The climate factors driving LUE dynamics were spatially heterogeneous in grasslands. Increasing precipitation accelerated the interannual growth rate of LUE in temperate steppe, and increasing temperature accelerated the interannual growth rate of LUE in other types. In addition, the temporal dynamic of LUE showed different trends in relation to time scales, and the growth trend slowed down after 1998. Our results should be considered in developing future grassland management measures and predicting carbon cycle–climate interactions.

Seasonal variations and drivers of energy fluxes and partitioning along an aridity gradient in temperate grasslands of Northern China

Surface energy exchange is vital because it affects microclimate, water cycle and biogeochemical processes in the canopy-atmosphere interface. In this study, seasonal variations and regulators of energy fluxes and partitioning were investigated based on a long-term eddy flux observation dataset (12 towers, 82 site-years in total) along an aridity gradient in temperate grasslands of Northern China. Our results showed that the net radiation (Rn) and all energy components, including latent heat (LE), sensible heat (H) and ground heat (G0) fluxes, presented unimodal seasonal patterns across different grassland types, with Rn and LE peaked in the middle growing season but H and G0 at the beginning of the growing season. The energy partitioning shifted from the H-dominated to the LE-dominated period accompanied vegetation phenological development, thus a U-shaped seasonal pattern of Bowen ratio (β, H/LE) was observed. Prolonged LE-dominated period and great peak of LE flux enhanced LE/Rn proportion and decreased β from desert steppes to typical steppes and meadow steppes. Climate and vegetation factors co-regulated the seasonal patterns of energy fluxes and partitioning, with enhanced effects of LAI and canopy surface conductance (gc) from desert steppes to typical and meadow steppes, but a reverse pattern of land-atmosphere coupling via vegetation physiological regulation. Meanwhile, enhanced sensitivity of β in response to variations of climate and vegetation factors was also observed with increasing aridity. Our founding highlighted the role of vegetation especially physiological regulation in determining the seasonal patterns of energy fluxes and partitioning in water-limited grasslands. Whereas, the great sensitivity of energy partitioning to vegetation changing with increasing aridity also emphasized that it is vital to pay attention to the response of energy exchange in the desert steppes to the greening trend in Northern China under future climate scenarios.

Untangling the effects of climate variation and human interference on grassland dynamics in North China

AbstractClimatic and anthropogenic disturbances play pivotal roles in shaping the dynamics of grassland. Quantifying their impacts on grassland variation is essential to ensure sustainable grassland management. In this study, we employed the Thornthwaite Memorial and Carnegie–Ames–Stanford‐approach (CASA) models to investigate the spatiotemporal effects of these two variables on grassland variation in northern China from 2000 to 2016, using the net primary productivity (NPP) as a measure. Our findings reveal that approximately 25.92% of the grassland in northern China experienced degradation, while restored grasslands occupied 45% of the total grassland area. The average grassland actual NPP (ANPP) and human‐induced NPP decreased at rates of −0.60 and −5.62 gC m−2 a−1, respectively. Conversely, potential NPP exhibited an upward trend with an average increase of 2.27 gC m−2 a−1. Furthermore, grassland ANPP showed a projected increase in most parts of northern China. Climate change emerged as the primary driver for grassland restoration in Xinjiang, Qinghai, and Inner Mongolia, leading to an increase of 21582.79 Gg C in grassland NPP. In contrast, human activities were the dominant catalysts for grassland degradation, resulting in a reduction of 51932.3 Gg C in grassland NPP. Human‐induced grassland degradation was ubiquitous in northwest and northeast China. With the exception of slope grassland, climate change primarily influenced the restoration of most grassland types, while human activities were the primary cause of degradation. Our analysis indicated a strong correlation between temperature and grassland degradation, while precipitation played a pivotal role in grassland restoration in northern China. Human interference demonstrated both positive and negative impacts on grassland changes. In conclusion, the increase in precipitation and the implementation of ecological restoration plans have effectively promoted the restoration of grasslands in northern China.

Alteration of microbial carbon and nitrogen metabolism within the soil metagenome with grazing intensity at semiarid steppe

Grazing causes changes in microbiome metabolic pathways affecting plant growth and soil physicochemical properties. However, how grazing intensity affects microbial processes is poorly understood. In semiarid steppe grassland in northern China, shotgun metagenome sequencing was used to investigate variations in soil carbon (C) and nitrogen (N) cycling-related genes after six years of the following grazing intensities: G0, control, no grazing; G1, 170 sheep days ha−1 year−1; G2, 340 sheep days ha−1 year−1; and G3, 510 sheep days ha−1 year−1. Taxa and functions of the soil microbiome associated with the C cycle decreased with increasing grazing intensity. Abundances of genes involved in C fixation and organic matter decomposition were altered in grazed sites, which could effects on vegetation decomposition and soil dissolved organic carbon (DOC) content. Compared with the control, the abundances of nitrification genes were higher in G1, but the abundances of N reduction and denitrification genes were lower, suggesting that light grazing promoted nitrification, inhibited denitrification, and increased soil NO3− content. Q-PCR further revealed that the copies of genes responsible for carbon fixation (cbbL) and denitrification (norB) decreased with increasing grazing intensity. The highest copy numbers of the nitrification genes AOA and AOB were in G1, whereas copy numbers of the denitrification gene nirK were the lowest. A multivariate regression tree indicated that changes in C fixation genes were linked to changes in soil DOC content, whereas soil NO3− content was linked with nitrification and denitrification under grazing. Thus, genes associated with C fixation and the N cycle affected how C fixation and N storage influenced soil physicochemical properties under grazing. The findings indicate that grazing intensity affected C and N metabolism. Proper grassland management regimes (e.g., G1) are beneficial to the balances between ecological protection of grasslands and plant production in the semiarid steppe.

Soil properties and anthropogenic influences control the distribution of soil organic carbon in grasslands of northern China

AbstractSoil organic carbon (SOC) in grasslands not only plays an important role in carbon cycle but also largely affects soil function and thus determines grasslands' productivity. However, the influence mechanism of different factors on SOC storage in grasslands of northern China remains unclear. Based on an extensive field investigation and multiple statistical approaches, we mapped SOC of the grassland in northern China, and explored their correlations with climatic factors, biological factors, human activity intensity (HAI), and soil physicochemical factors. The effects of these factors on SOC were also analyzed by structural equation model. The results showed that the SOC varied across the regions and was strongly correlated with soil chemical factors (i.e., soil total nitrogen [TN], amorphous Al, and amorphous Fe) and soil physical factors (i.e., clay, silt, and sand). HAI, which was mainly influenced by grazing, had a significant but negative impact on SOC. Different from previous studies, we found that climatic factors such as temperature and precipitation indirectly affected SOC by influencing biological factors such as vegetation coverage, vegetation height, Shannon–Weiner index, and species richness. The soil physicochemical properties and HAI were the dominant influencing factors for controlling SOC distribution in the grasslands of northern China. Our findings will further increase the understanding of the carbon cycle in grassland ecosystems, while providing important scientific references for temperate grassland ecosystem management.

Integrating vegetation phenological characteristics and polarization features with object-oriented techniques for grassland type identification

ABSTRACT Due to the small size, variety, and high degree of mixing of herbaceous vegetation, remote sensing-based identification of grassland types primarily focuses on extracting major grassland categories, lacking detailed depiction. This limitation significantly hampers the development of effective evaluation and fine supervision for the rational utilization of grassland resources. To address this issue, this study concentrates on the representative grassland of Zhenglan Banner in Inner Mongolia as the study area. It integrates the strengths of Sentinel-1 and Sentinel-2 active-passive synergistic observations and introduces innovative object-oriented techniques for grassland type classification, thereby enhancing the accuracy and refinement of grassland classification. The results demonstrate the following: (1) To meet the supervision requirements of grassland resources, we propose a grassland type classification system based on remote sensing and the vegetation-habitat classification method, specifically applicable to natural grasslands in northern China. (2) By utilizing the high-spatial-resolution Normalized Difference Vegetation Index (NDVI) synthesized through the Spatial and Temporal Non-Local Filter-based Fusion Model (STNLFFM), we are able to capture the NDVI time profiles of grassland types, accurately extract vegetation phenological information within the year, and further enhance the temporal resolution. (3) The integration of multi-seasonal spectral, polarization, and phenological characteristics significantly improves the classification accuracy of grassland types. The overall accuracy reaches 82.61%, with a kappa coefficient of 0.79. Compared to using only multi-seasonal spectral features, the accuracy and kappa coefficient have improved by 15.94% and 0.19, respectively. Notably, the accuracy improvement of the gently sloping steppe is the highest, exceeding 38%. (4) Sandy grassland is the most widespread in the study area, and the growth season of grassland vegetation mainly occurs from May to September. The sandy meadow exhibits a longer growing season compared with typical grassland and meadow, and the distinct differences in phenological characteristics contribute to the accurate identification of various grassland types.

Development and application of a vegetation degradation classification approach for the temperate grasslands of northern China

To establish a unified grassland degradation assessment system, this study proposed a classification approach using a statistical method based on the percent decrease in the annual maximum leaf area index from a long time series of remote sensing data. The obtained classification thresholds for vegetation degradation were temporally stable and spatially universal and were thus well-suited as a new standard. They were specific for different temperate grassland types and applicable to large and heterogeneous areas. Meadow steppes had the lowest degradation thresholds, sensitive to changes in plant growth, desert-related steppes had the highest thresholds, and typical steppes had intermediate thresholds. We then used the obtained thresholds to assess the degradation status of temperate grasslands in northern China from 1981 to 2017. Degraded grasslands accounted for 8.2 % (1.72 × 107 ha), of which moderately, severely, and extremely severely degraded grasslands accounted for 38.6, 34.9, and 4.6 %, respectively. More than half (∼67 %) of the degraded grasslands in northern China occurred in the Inner Mongolia Autonomous Region, and these were dominated by severely degraded grasslands. About 20 % of all degraded grasslands in northern China occurred in the Xinjiang Uygur Autonomous Region, and were dominated by moderate degradation. These results were highly consistent with the Chinese national standard regarding the total degraded area. However, differences occurred in specific grassland degradation levels and grassland types. Therefore, compared with traditional approaches, the new approach provided a more accurate degradation assessment, which is crucial for protecting and restoring the different temperate grasslands of China.

Soil phosphorus availability alters the correlations between root phosphorus-uptake rates and net photosynthesis of dominant C3 and C4 species in a typical temperate grassland of Northern China.

Phosphorus (P) fertilization can alleviate a soil P deficiency in grassland ecosystems. Understanding plant functional traits that enhance P uptake can improve grassland management. We measured impacts of P addition on soil chemical and microbial properties, net photosynthetic rate (Pn ) and nonstructural carbohydrate concentrations ([NSC]), and root P-uptake rate (PUR), morphology, anatomy, and exudation of two dominant grass species: Leymus chinensis (C3 ) and Cleistogenes squarrosa (C4 ). For L. chinensis, PUR and Pn showed a nonlinear correlation. Growing more adventitious roots compensated for the decrease in P transport per unit root length, so that it maintained a high PUR. For C. squarrosa, PUR and Pn presented a linear correlation. Increased Pn was associated with modifications in root morphology, which further enhanced its PUR and a greater surplus of photosynthate and significantly stimulated root exudation (proxied by leaf [Mn]), which had a greater impact on rhizosheath micro-environment and microbial PLFAs. Our results present correlations between the PUR and the Pn of L. chinensis and C. squarrosa and reveal that NSC appeared to drive the modifications of root morphology and exudation; they provide more objective basis for more efficient P-input in grasslands to address the urgent problem of P deficiency.

Plant traits modulate grassland stability during drought and post‐drought periods

Abstract Grasslands are subject to climate change, such as severe drought, and an important aspect of their functioning is temporal stability in response to extreme climate events. Previous research has explored the impacts of extreme drought and post‐drought periods on grassland stability, yet the mechanistic pathways behind these changes have rarely been studied. Here, we implemented an experiment with 4 years of drought and 3 years of recovery to assess the effects of drought and post‐drought on the temporal stability of above‐ground net primary productivity (ANPP) and its underlying mechanisms. To do so, we measured community‐weighted mean (CWM) of six plant growth and nine seed traits, functional diversity, population stability and species asynchrony across two cold, semiarid grasslands in northern China. We also performed piecewise structural equation models (SEMs) to assess the relationships between ANPP stability and its underlying mechanisms and how drought and post‐drought periods alter the relative contribution of these mechanisms to ANPP stability. We found that temporal stability of ANPP was not reduced during drought due to grasses maintaining productivity, which compensated for increased variation of forb productivity. Moreover, ANPP recovered rapidly after drought, and both grasses and forbs contributed to community stability during the post‐drought period. Overall, ANPP stability decreased during the combined drought and post‐drought periods because of rapid changes in ANPP from drought to post‐drought. SEMs revealed that the temporal stability of ANPP during drought and post‐drought periods was modulated by functional diversity and community‐weighted mean traits directly and indirectly by altering species asynchrony and population stability. Specifically, the temporal stability of ANPP was positively correlated with functional divergence of plant communities. CWMs of seed traits (e.g. seed width and thickness), rather than plant growth traits (e.g. specific leaf area and leaf nutrient content), stabilized grassland ANPP. Productivity of plant communities with large and thick seeds was less sensitive to precipitation changes over time. These results emphasize the importance of considering both the functional trait distribution among species and seed traits of dominant species since their combined effects can stabilize ecosystem functions under global climate change scenarios. Read the free Plain Language Summary for this article on the Journal blog.