Stipa Grandis Research Articles

Adaptive grazing enhances plant species richness and density in the soil seed bank in a semi-arid grassland

The soil seed bank plays a key role in vegetation resilience under environmental disturbances, and is especially important for the restoration of degraded vegetation. However, the responsive dynamics of the soil seed bank to animal grazing and its potential in the restoration of grazing degraded steppe grassland remain unclear. Here we examined the changes in plant species diversity and density in both the soil seed bank and the aboveground vegetation of a natural grassland along an experimental gradient of four grazing intensities (nil, light, moderate and heavy grazing) in an adaptive grazing management system that ensures grassland residual cover was always above a certain criteria. The grassland is a typical steppe dominated by Leymus chinensis, Stipa grandis, and Cleistogenes squarrosa in central Inner Mongolia, China. We found that (i) plant species richness and density of the seed bank in the top 10 cm soil layer increased with grazing intensity, though the density of the seed bank in the top 5 cm soil layer showed an decrease. (ii) Moderate and heavy grazing significantly decreased the density of perennial but increased annual and biennial plants in the top 5 cm soil layer, which dominate the changes in the top 10 cm soil layer. (iii) Plant species richness and density in the aboveground vegetation also increased with grazing intensity, so did the similarity between the species composition of the soil seed bank and aboveground vegetation in the top 10 cm. The increase in the richness and density of annual and biennial species dominated the responsive changes to grazing of the soil seed bank and aboveground vegetation in the studied grassland. Our results provide a reference basis for grazing management in the region from the perspective of the soil seed bank, and suggest that the adaptive grazing system with grassland residual height controlled above a criterion benefits to the soil seed bank thus the re-generation of vegetation.

Correlations between root phosphorus acquisition and foliar phosphorus allocation reveal how grazing promotes plant phosphorus utilization

Overgrazing and phosphorus (P) deficiency are two major factors limiting the sustainable development of grassland ecosystems. Exploring plant P utilization and acquisition strategies under grazing can provide a solid basis for determining a reasonable grazing intensity. Both foliar P allocation and root P acquisition are crucial mechanisms for plants to adapt to environmental P availability; however, their changing characteristics and correlation under grazing remain unknown. Here, we investigated foliar P fractions, root P-acquisition traits and gene expression, as well as rhizosphere and bulk soil properties of two dominant plant species, Leymus chinensis (a rhizomatous grass) and Stipa grandis (a bunchgrass), in a field grazing intensity gradient site in Inner Mongolia. Grazing induced different degrees of compensatory growth in the two dominant plant species, increased rhizosphere P availability, and alleviated plant P limitation. Under grazing, the foliar metabolite P of L. chinensis increased, whereas the nucleic acid P of S. grandis increased. Increased P fractions in L. chinensis were positively correlated with increased root exudates and rapid inorganic P absorption. For S. grandis, increased foliar P fractions were positively correlated with more fine roots, more root exudates, and up-regulated expression of genes involved in defense and P metabolism. Overall, efficient root P mobilization and uptake traits, as well as increases in leaf metabolic activity-related P fractions, supported plant compensatory growth under grazing, a process that differed between tiller types. The highest plant productivity and leaf metabolic activity-related P concentrations under medium grazing intensity clarify the underlying basis for sustainable livestock production.

Investigation into the Effects of Different Restoration Techniques on the Soil Nutrient Status in Degraded Stipa grandis Grassland

The degradation and desertification of grassland ecosystems have garnered significant attention both domestically and internationally. Grassland restoration techniques are widely considered a principal measure to promote the sustainable utilization of grasslands, with soil nutrient content being a core indicator for assessing the effectiveness of restoration in degraded grasslands. This study aims to explore the differential impacts of various grassland restoration methods on soil nutrient distribution in degraded Stipa grandis grasslands. Three major restoration methods, i.e., root cutting, enclosure, and fertilization, were applied in the study area. The soil nutrient content was measured and analyzed under the different restoration methods and at varying depths. The results revealed that under all three restoration methods and at different soil depths (0–10 cm, 10–20 cm, 20–30 cm), the organic matter, total nitrogen, total phosphorus, alkali-hydrolyzable nitrogen, alkali-hydrolyzable phosphorus, and available potassium contents were significantly higher than those in the control group (p < 0.05). Furthermore, as soil depth increased, the contents of organic matter and all nutrients gradually decreased. Specifically, regarding the contents of different nutrients, the order of organic matter, total nitrogen, total phosphorus, alkali-hydrolyzable nitrogen, and available phosphorus was as follows: fertilization > enclosure > root cutting > control, while the contents of total potassium and available potassium followed the sequence: fertilization > enclosure > control > root cutting. Additionally, based on the canonical correlation analysis (R2 = 0.88), the total phosphorus content in soil had the greatest impact on soil nutrients, while vegetation cover and plant height contributed the most to vegetation characteristics. In grassland restoration, the increase in soil total phosphorus led to higher vegetation cover and height, mildly influenced plant diversity and density, and simultaneously promoted biomass accumulation. These research findings provide a solid theoretical foundation for the application of grassland restoration techniques, contributing to the sustainable development of grassland ecosystems.

Endophytic infection increases the belowground over-yielding effects of the host grass community mainly by increasing the complementary effects.

Increases in plant species diversity may increase the community diversity effect and produce community over-yielding. Epichloë endophytes, as symbiotic microorganisms, are also capable of regulating plant communities, but their effects on community diversity effects are often overlooked. In this experiment, we investigated the effects of endophytes on the diversity effects of host plant community biomass by constructing artificial communities with 1-species monocultures and 2- and 4-species mixtures of endophyte-infected (E+) and endophyte-free (E-) Achnatherum sibiricum and three common plants in its native habitat, which were potted in live and sterilized soil. The results showed that endophyte infection significantly increased the belowground biomass and abundance of Cleistogenes squarrosa, marginally significantly increased the abundance of Stipa grandis and significantly increased the community diversity (evenness) of the 4-species mixtures. Endophyte infection also significantly increased the over-yielding effects on belowground biomass of the 4-species mixtures in the live soil, and the increase in diversity effects on belowground biomass was mainly due to the endophyte significantly increasing the complementary effects on belowground biomass. The effects of soil microorganisms on the diversity effects on belowground biomass of the 4-species mixtures were mainly derived from their influences on the complementary effects. The effects of endophytes and soil microorganisms on the diversity effects on belowground biomass of the 4-species communities were independent, and both contributed similarly to the complementary effects on belowground biomass. The finding that endophyte infection promotes belowground over-yielding in live soil at higher levels of species diversity suggests that endophytes may be one of the factors contributing to the positive relationship between species diversity and productivity and explains the stable co-existence of endophyte-infected Achnatherum sibiricum with a variety of plants in the Inner Mongolian grasslands.

Soil Moisture Inversion in Grassland Ecosystem Using Remote Sensing Considering Different Grazing Intensities and Growing Seasons

Although vegetation community information such as grazing gradient, biomass, and density have been well characterized in typical grassland communities with Stipa grandis and Leymus chinensis as dominant species, their impact on the soil moisture (SM) inversion is still unclear. This study investigated the characteristics of a grassland vegetation community at different grazing gradients and growing seasons and its impact on SM inversion using remote sensing data. The water cloud model (WCM) was used for SM inversion, and both field and remote sensing data collected from 2019 to 2021 were used for calibration and prediction. The study found that the calibrated WCM achieved prediction results of SM inversion with average R2 values of 0.41 and 0.38 at different grazing gradients and growing seasons, respectively. Vegetation biomass and height were significantly correlated with vegetation indexes, and the highest model prediction accuracy was achieved for biomass and height around 121.1 g/m2 [102.3–139.9] and 18.6 cm [17.3–19.8], respectively. Generally, NDWI1 produced higher SM estimation accuracy than NDWI2. The growing season of vegetation also affects the accuracy of the WCM to retrieve SM, with the highest accuracy achieved in mid-growing season I. Therefore, the developed WCM with optimal height and biomass of vegetation communities can enhance the SM prediction capacity; it thus can be potentially used for SM prediction in typical grasslands.

Effects of intra-annual precipitation patterns on grassland productivity moderated by the dominant species phenology.

Phenology and productivity are important functional indicators of grassland ecosystems. However, our understanding of how intra-annual precipitation patterns affect plant phenology and productivity in grasslands is still limited. Here, we conducted a two-year precipitation manipulation experiment to explore the responses of plant phenology and productivity to intra-annual precipitation patterns at the community and dominant species levels in a temperate grassland. We found that increased early growing season precipitation enhanced the above-ground biomass of the dominant rhizome grass, Leymus chinensis, by advancing its flowering date, while increased late growing season precipitation increased the above-ground biomass of the dominant bunchgrass, Stipa grandis, by delaying senescence. The complementary effects in phenology and biomass of the dominant species, L. chinensis and S. grandis, maintained stable dynamics of the community above-ground biomass under intra-annual precipitation pattern variations. Our results highlight the critical role that intra-annual precipitation and soil moisture patterns play in the phenology of temperate grasslands. By understanding the response of phenology to intra-annual precipitation patterns, we can more accurately predict the productivity of temperate grasslands under future climate change.

The trade-offs of ecological functions during community restoration in Stipa grandis steppe

The trade-offs of ecological functions during community restoration in Stipa grandis steppe

Runoff and Infiltration responses of revegetated slopes to clipping management on the northern Loess Plateau

Large-scale vegetation restoration can reduce local watershed water yield, limit vegetation establishment and subsequent growth, and influence regional ecosystem functions. Clipping management by reducing aboveground parts of grassland was gradually recommended and adopted in Grain-for-Green project management to offset these additional issues. Thus, scientific evaluation of the effectiveness of clipping management on infiltration and runoff processes is necessary for maintaining the stability of the surface water system and the sustainability of vegetation restoration in semi-arid regions. A field simulated rainfall experiment was conducted with four managed clipping grasslands (mainly bunge needlegrass and Stipa grandis), including no clipping, light clipping, heavy clipping, and complete clipping under three slope gradients (10, 20, and 30°) and three rainfall intensities (60, 90, and 120 mm/h) to explore the mechanism of runoff and infiltration responses to clipping using structural equation modeling and variation partitioning based on an SCS-CN model. The results showed the runoff coefficient of the light clipping, heavy clipping, and complete clipping plots were 1.33, 2.22, and 4.22 times that of the no clipping plot. The light clipping, heavy clipping, and complete clipping plots decreased the infiltration coefficients by 0%, 5%, and 26% relative to the no clipping plot. Rainfall intensity dominated runoff and infiltration amounts, and clipping intensity's total effect was stronger than slope gradient. Clipping intensity and slope gradient were more influential on runoff with increasing rainfall intensity. The mutual inhibition effect was between clipping intensity and slope gradient on runoff. In order to maintain the sustainability of restoration, a 25–50% vegetation coverage after clipping maximizes the benefits of increasing runoff and maintaining enough soil water supply that prevents possible soil drought. We propose that future vegetation restoration policies should evaluate the appropriate clipping intensity; meanwhile, local physiographic and climate conditions should be considered. These findings may offer guidance for the development of measures for runoff regulation and ecosystem functions of the watershed during vegetation restoration on the northern Loess Plateau.

Identification of Constructive Species and Degraded Plant Species in the Temperate Typical Grassland of Inner Mongolia Based on Hyperspectral Data

In recent years, grassland degradation has become a global ecological problem. The identification of degraded grassland species is of great significance for monitoring grassland ecological environments and accelerating grassland ecological restoration. In this study, a ground spectral measurement experiment of typical grass species in the typical temperate grassland of Inner Mongolia was performed. An SVC XHR-1024i spectrometer was used to obtain field measurements of the spectra of grass species in the typical grassland areas of the study region from 6–29 July 2021. The parametric characteristics of the grass species’ spectral data were extracted and analyzed. Then, the spectral characteristic parameters + vegetation index, first-order derivative (FD) and continuum removal (CR) datasets were constructed by using principal component analysis (PCA). Finally, the RF, SVM, BP, CNN and the improved CNN model were established to identify Stipa grandis (SG), Cleistogenes squarrosa (CS), Caragana microphylla Lam. (CL), Leymus chinensis (LC), Artemisia frigida (AF), Allium ramosum L. (AL) and Artemisia capillaris Thunb. (AT). This study aims to determine a high-precision identification method based on the measured spectrum and to lay a foundation for related research. The obtained research results show that in the identification results based on ground-measured spectral data, the overall accuracy of the RF model and SVM model identification for different input datasets is low, but the identification accuracies of the SVM model for AF and AL are more than 85%. The recognition result of the CNN model is generally worse than that of the BP neural network model, but its recognition accuracy for AL is higher, while the recognition effect of the BP neural network model for CL is better. The overall accuracy and average accuracy of the improved CNN model are all the highest, and the recognition accuracy of AF and CL is stable above 98%, but the recognition accuracy of CS needs to be improved. The improved CNN model in this study shows a relatively significant grass species recognition performance and has certain recognition advantages. The identification of degraded grassland species can provide important scientific references for the realization of normal functions of grassland ecosystems, the maintenance of grassland biodiversity richness, and the management and planning of grassland production and life.

Mechanism for the restoration of degraded typical steppe by nitrogen and phosphorus co-addition.

The reduction of soil nutrient content is one of the major reasons caused grassland degradation in China. Nutrient addition is thus considered as an effective measure for the restoration of degraded grasslands. However, over-fertilization can lead to decrease in plant diversity. To clarify the appropriate amount of nutrient addition and the underlying mechanism that promotes grassland restoration, we set up a nitrogen and phosphorus co-addition experiment in a degraded typical steppe of Inner Mongolia, and examined the responses at community, functional group and species levels to nutrient addition. The results showed that nutrient addition enhanced biomass while did not reduce species richness at the community level. The biomass showed a saturation response with the increases of nutrient addition, which approached saturation under the 12.0 g N·m-2, 3.8 g P·m-2 treatment. Species richness increased significantly under the lower nutrient treatments (N <9.6 g·m-2, P < 3.0 g·m-2) compared with the control, while the two high nutrient treatments did not alter species richness. At the functional group level, biomass and abundance of perennial rhizome grasses increased significantly with the increases of nutrient addition levels. Biomass and density of annuals increased significantly under high nutrient addition levels. However, the abundance and biomass of perennial bunchgrasses and perennial forbs were rarely affected. At the species level, six target species responded differently to nutrient addition. Biomass of Leymus chinensis was significantly increased due to the increase of population density and individual biomass. Biomass of Stipa grandis, Agropyron cristatum and Cleistogenes squarrosa change little. Biomass of Potentilla acaulis and Carex korshinskyi were reduced due to the decreases in individual biomass and population density, respectively. As a measure of restoring degraded grassland, nutrient addition could significantly increase biomass and species diversity, decrease biomass of the degradation indicator species, and increase biomass of perennial rhizomes grasses.

Grazing promotes soil phosphorus cycling by enhancing soil microbial functional genes for phosphorus transformation in plant rhizosphere in a semi-arid natural grassland

Soil microorganisms play a key role in soil P transformation and cycling in grassland ecosystems, while the microbial mechanisms of animal grazing mediating soil P processes are not fully understood. We conducted a grazing experiment in a typical steppe grassland in Inner Mongolia, to explore the responses of microbial communities in rhizosphere and bulk soils to grazing intensity for understanding the mechanisms of grazing affecting P cycling. We determined soil physico-chemical properties and alkaline phosphatase activities, and measured soil microbial diversity and the relative abundance of microbial P-transformation genes by metagenomics in the rhizosphere and bulk soils of a Stipa grandis dominated grassland under three grazing intensities (no-, moderate, and heavy grazing). We found that (i) grazing significantly increased soil available P concentration and soil alkaline phosphatase activity; (ii) grazing increased the abundance of bacterial, but not fungal communities, and the enhanced abundance of rhizosphere bacteria promotes the P-cycling potential; (iii) grazing increased the relative abundance of the genes responsible for microbial P-uptake and transport, and inorganic P solubilization and organic P mineralization in rhizosphere soil, but not in bulk soil; (iv) grazing reduced the node degree of the network of the genes involved in P-transformation, but it increased the node degree of the genes encoding alkaline phosphatase and the C–P lyase multi-enzyme complex in the rhizosphere soil. The grazing-induced changes in the abundance of microbial functional genes are beneficial to P-solubilization and mineralization. Our results indicate a divergent effect of grazing on soil microbial communities and their functional genes involved P-transformation in rhizosphere and bulk soils, and represent an important progress towards the understanding of the mechanisms of microbial regulation of P cycling in grassland ecosystems.

Effects of Isolated LAB on Chemical Composition, Fermentation Quality and Bacterial Community of Stipa grandis Silage.

This study aimed to screen and identify lactic acid bacteria (LAB) strains from the Stipa grandis and naturally fermented silage, and assess their effects on the silage quality and bacterial community of Stipa grandis after 60 days of the fermentation process. A total of 38 LAB were isolated, and strains ZX301 and YX34 were identified as Lactiplantibacillus plantarum and Pediococcus pentosaceus using 16S rRNA sequences; they can normally grow at 10−30 °C, with a tolerance of pH and NaCl from 3.5 to 8.0 and 3 to 6.5%, respectively. Subsequently, the two isolated LAB and one commercial additive (Lactiplantibacillus plantarum) were added to Stipa grandis for ensiling for 60 days and recorded as the ZX301, YX34, and P treatments. The addition of LAB was added at 1 × 105 colony-forming unit/g of fresh weight, and the same amount of distilled water was sprayed to serve as a control treatment (CK). Compared to the CK treatment, the ZX301 and YX34 treatments exhibited a positive effect on pH reduction. The water-soluble carbohydrate content was significantly (p < 0.05) increased in ZX301, YX34, and P treatments than in CK treatment. At the genus level, the bacterial community in Stipa grandis silage involves a shift from Pantoea to Lactiplantibacillus. Compared to the CK treatment, the ZX301, YX34, and P treatments significantly (p < 0.05) increase the abundance of Pediococcus and Lactiplantibacillus, respectively. Consequently, the results indicated that the addition of LAB reconstructed microbiota and influenced silage quality. The strain ZX301 could improve the ensiling performance in Stipa grandis silage.

Multi-omics analysis reveals the molecular changes accompanying heavy-grazing-induced dwarfing of Stipa grandis.

Heavy grazing significantly reduces Stipa grandis growth. To enhance our understanding of plant responses to heavy grazing, we conducted transcriptomic, proteomic, and metabolic analyses of the leaves of non-grazed plants (NG) and heavy-grazing-induced dwarf plants (HG) of S. grandis. A total of 101 metabolites, 167 proteins, and 1,268 genes differed in abundance between the HG and NG groups. Analysis of Kyoto Encyclopedia of Genes and Genomes pathways among differentially accumulated metabolites (DAMs) revealed that the most enriched pathways were flavone and flavonol biosynthesis, tryptophan metabolism, and phenylpropanoid biosynthesis. An integrative analysis of differentially expressed genes (DEGs) and proteins, and DAMs in these three pathways was performed. Heavy-grazing-induced dwarfism decreased the accumulation of DAMs enriched in phenylpropanoid biosynthesis, among which four DAMs were associated with lignin biosynthesis. In contrast, all DAMs enriched in flavone and flavonol biosynthesis and tryptophan metabolism showed increased accumulation in HG compared with NG plants. Among the DAMs enriched in tryptophan metabolism, three were involved in tryptophan-dependent IAA biosynthesis. Some of the DEGs and proteins enriched in these pathways showed different expression trends. The results indicated that these pathways play important roles in the regulation of growth and grazing-associated stress adaptions of S. grandis. This study enriches the knowledge of the mechanism of heavy-grazing-induced growth inhibition of S. grandis and provides valuable information for restoration of the productivity in degraded grassland.

Effects of Grazing on Soil Organic Carbon in the Rhizosphere of Stipa Grandis in a Typical Steppe of Inner Mongolia, China

The ability of grassland ecosystems to sequester carbon has a great potential to achieve carbon neutralization. Rhizosphere deposition is the most uncertain part of the soil carbon cycle. Since grazing is one of the main ways to utilize grasslands, we conducted experiments to clarify the role of rhizosphere on soil organic carbon (SOC) cycling under grazing in a typical steppe region of Inner Mongolia, China. The experiment was conducted in grasslands under light, moderate, and heavy grazing and in a control (no grazing) in Inner Mongolia, China. Here, we present our analysis of the total soil organic carbon (TOC) and fractions in both the rhizosphere and bulk soil. Light and moderate grazing increased SOC contents in rhizosphere soil, and we found more SOC in rhizosphere soil than in bulk soil. The rhizosphere showed SOC enrichment effect, and this effect increased with an increase in grazing intensity. As grazing intensity increased, microbial biomass carbon content and its percentage of TOC increased in rhizosphere soil and were more stable than those in bulk soil. Dissolved organic carbon content and its percentage of TOC also increased in rhizosphere soil with increasing grazing intensity. These changes were more than those observed in bulk soil. Changes in potentially mineralizable carbon and particulate organic carbon in the rhizosphere and bulk soil were not synchronized in plots under different grazing intensities. Grazing changed the quantity of bacteria, fungi, and actinomycetes, as well as the community structure of soil microbes, in rhizosphere soil and bulk soil. It also influenced the content and structure of SOC. Acidic components (e.g., organic acids) of root exudate reduced the pH in rhizosphere soil to less than that in bulk soil, which may have affected SOC cycling. The results can provide support to improve the ecosystem carbon sink function and help to achieve the goal of carbon peaking/carbon neutral target.

Differential Responses of Dominant Plants to Grazing in Typical Temperate Grassland in Inner Mongolia

Leymus chinensis, Stipa grandis, Artemisia frigida, and Cleistogenes squarrosa are the dominant plant species in typical temperate grasslands in Xilingol. Intensive studies related to overgrazing, which resulted in a dominant plant shift, have been carried out in recent years, but the ways in which these four species respond to different grazing intensities remain elusive. In this study, the contents of primary metabolites, secondary metabolites, and phytohormones in the leaves of these species under five grazing intensities were assayed and compared. The results showed that A. frigida contained higher amounts of lignin, while C. squarrosa contained higher amounts of total flavonoids than the other species. Leymus chinensis showed a different accumulation of cellulose and tannin in response to grazing, compared with the other three species. Stipa grandis and A. frigida increased in soluble protein contents in response to different grazing treatments. In particular, the contents of phytohormones, such as abscisic acid, salicylic acid, and gibberellins, were markedly changed under grazing. Leymus chinensis exhibited different abscisic acid and gibberellins accumulation patterns compared with the other species, under the different grazing intensities. Patterns of salicylic acid accumulation were similar (except under light and moderate grazing intensities in A. frigida) among the four species. The results indicated that the four species differed in adaptive strategies to cope with the different grazing intensities, and phytohormones played important roles in coordinating the regulation of their growth and grazing tolerance. This study provides a foundation for elucidating the mechanisms of overgrazing-induced degradation of the Xilingol grassland.

Seasonal grazing alters nutrient resorption and conservation, and affects spring growth ofStipa grandis

AbstractNutrient resorption in autumn is a key mechanism of perennial plants for nutrient conservation and efficient use in grassland. Grazing effects on plant nutrient resorption may alter root nutrient conservation and affect plant growth in the subsequent spring. There are many studies on nutrient resorption and conservation of plants in grazing grassland, but few studies have investigated the effect of grazing on plant growth in subsequent spring. Taking Stipa grandis, a dominant perennial grass in a semi-arid steppe as a model plant, we examined plant nitrogen (N) and phosphorous (P) resorption traits (resorption efficiency, proficiency and flux) and root nutrient conservation traits (root biomass and nutrient pool) in autumn, and plant growth traits (height, biomass and nutrient pool) in the subsequent spring, in an experimental grassland under four grazing season treatments (i.e. grazing in spring, summer or autumn or no grazing). We found that (i) 51%–66% of N and 58%–80% of P in S. grandis shoots were resorbed in autumn, and the resorption flux was the lowest under autumn grazing, and highest under spring grazing. (ii) Root nutrient conservation traits were significantly reduced by summer grazing, slightly decreased by spring grazing, but not affected by autumn grazing. (iii) Plant growth in next spring was the best under early spring grazing and the worst under autumn grazing, which was mainly affected by soil moisture rather than root nutrient storage. Our study provides insights into the process of plant nutrient cycling and a theoretical basis for establishing grazing system for grassland protection and rational utilization.

Rhizosphere priming effect of four non-woody perennials after leaf senescence and before shoot regrowth

Living roots and its rhizodeposition can stimulate or retard soil organic matter (SOM) decomposition via the rhizosphere priming effect (RPE). However, little is known about the RPE during non-growing seasons. In this study, we measured the RPEs of two perennial grasses (Elymus dahuricus, Stipa grandis) and two legumes (Medicago sativa, Melissilus ruthenicus) after leaf senescence and before shoot regrowth using a 13C natural tracer method. All four species produced positive RPEs at each sampling time, with the magnitude ranging from 40% to 238% compared to unplanted soil. Further, the inter-specific variation in the RPE during the non-growing season was partly explained by the root:shoot ratio, average root diameter and root tissue density. Overall, these results demonstrate that live roots of non-woody perennials could accelerate SOM decomposition even during the non-growing season.

Summer grazing by three livestock species at moderate intensity enhances primary productivity and drives community divergence in a semi‐arid steppe

AbstractAimsThe general effects of grazing by large herbivores on plant species composition and productivity are well known. Meanwhile, how different livestock species affect community structure is not fully understood. In northern China, livestock species composition is changing rapidly and hence, it is imperative to understand the resulting effects on grassland productivity and composition.LocationXilingol, Inner Mongolia, China.MethodsWe studied how grazing by three major livestock species affects typical steppe dominated by Leymus chinensis, Stipa grandis, Cleistogenes squarrosa and Carex korshinskyi, in a 4‐year field experiment using a random block‐design with four treatments (sheep, goat, cattle, no grazing), under summer grazing at moderate intensity. We calculated above‐ground net primary productivity (ANPP) and a selectivity index (SI) based on biomass to quantify livestock forage preferences.ResultWe found that (i) sheep preferred Leymus chinensis and mixed subordinate species, cattle preferred Stipa grandis, and goat preferred Carex korshinskyi and Cleistogenes squarrosa. (ii) Consistent with these preferences, sheep increased the relative biomass of Stipa grandis, but reduced that of Carex korshinskyi; cattle reduced the relative biomass of Stipa grandis and Carex korshinskyi but increased that of mixed subordinate species; and goats reduced the relative biomass of Cleistogenes squarrosa and Carex korshinskyi but increased that of mixed subordinate species. (iii) Overall, grazing significantly increased ANPP, mainly due to an increase in ANPP of Leymus chinensis and subordinate species, at the cost of Stipa grandis.ConclusionsSummer grazing by different livestock species at moderate intensity can increase ANPP, while livestock forage preferences can drive divergent changes in species composition. Our results also imply that livestock composition can be used as a mean to manage vegetation dynamics.

Variations in Plant Water Use Efficiency Response to Manipulated Precipitation in a Temperate Grassland

Water use efficiency (WUE) plays important role in understanding the interaction between carbon and water cycles in the plant-soil-atmosphere system. However, little is known regarding the impact of altered precipitation on plant WUE in arid and semi-arid regions. The study examined the effects of altered precipitation [i.e., ambient precipitation (100% of natural precipitation), decreased precipitation (DP, −50%) and increased precipitation (IP, +50%)] on the WUE of grass species (Stipa grandis and Stipa bungeana) and forb species (Artemisia gmelinii) in a temperate grassland. The results found that WUE was significantly affected by growth stages, precipitation and plant species. DP increased the WUE of S. grandis and S. bungeana generally, but IP decreased WUE especially in A. gmelinii. And the grasses had the higher WUE than forbs. For different growth stages, the WUE in the initial growth stage was lower than that in the middle and late growth stages. Soil temperature, available nutrients (i.e., NO3–, NH4+, and AP) and microorganisms under the altered precipitations were the main factors affecting plant WUE. These findings highlighted that the grasses have higher WUE than forbs, which can be given priority to vegetation restoration in arid and semi-arid areas.

Leaf Carbon Exchange of Two Dominant Plant Species Impacted by Water and Nitrogen Application in a Semi-Arid Temperate Steppe.

Photosynthetic characteristics are widely used as indicators of plant responses to global environmental changes such as precipitation change and nitrogen (N) deposition increase. How different plant species respond physiologically to the future precipitation change combined with increasing N availability is largely unclear. A field experiment was conducted to study responses in seasonal and interannual leaf carbon (C) exchange of two dominant plant species, Leymus chinensis and Stipa grandis, to additional water (either as spring snow or as summer water) and N application in a semi-arid temperate steppe of China. Our results showed that spring snow and summer water addition both increased the maximum photosynthetic rate (Amax) of two dominant species. Such effect was likely caused by raised light saturation point, the maximum apparent quantum yield, stomatal conductance, and transpiration rate. The N application combined with spring snow or summer water addition both enhanced Amax of S. grandis in both experimental years, whereas N application only increased Amax of L. chinensis combined with summer water addition. Their responses were attributed to a concurrent increase in leaf N concentration (Nleaf) and decrease in leaf phosphorus (P) concentration (Pleaf), indicating that Nleaf and Pleaf affect photosynthetic characteristics to regulate leaf C exchange. Our results suggest that differentiated responses among different species in photosynthetic characteristics may lead to changes in ecosystem structure and functioning under increasing precipitation and N deposition.