Aims In the context of global climate change, frequent extreme precipitation events will affect the soil nitrogen transformation processes in the semi-arid steppe. However, it remains unclear how the key processes of soil nitrogen transformation respond to precipitation change and how the total nitrogen mineralization rate is sensitive to different precipitation levels.

Methods This study was conducted on the meadow steppe, typical steppe, and desert steppe of the Global Change Network test platform of the northern China Steppe. In this study, the gross nitrogen mineralization rate (GNM) and gross nitrification rate (GN) of soil were measured by the ¹⁵N isotopic pool dilution method, as well as related biological (microbial biomass carbon content, microbial biomass nitrogen content, background biomass (BGB)), and abiotic (soil temperature (ST), soil water content (SWC)), soil substrate (soil ammonium nitrogen (NH₄⁺-N) content, nitrate nitrogen (NO^-₃-N) content, soluble organic carbon content, soluble organic nitrogen content) indexes.

Important findings The results showed significant differences in GNM among different steppe types. The highest GNM was in meadow steppe ((3.284 ± 0.613) mg·kg^-1·d^-1), followed by typical steppe ((1.370 ± 0.167) mg·kg^-1·d^-1) and desert steppe ((0.724 ± 0.216) mg·kg^-1·d^-1). However, the 50% decrease in precipitation had no significant effects on the GNM and GN of the three grasslands. The sensitivity of GNM and GN to precipitation reduction in typical steppe and desert steppe soil was significantly higher than that of precipitation increase. In contrast, the sensitivity of GNM and GN in meadow steppe soil was not significantly different between precipitation increase and decrease. Structural equation model (SEM) analysis revealed that SWC was the main factor affecting the soil GNM. These results indicate that short-term extreme precipitation has no significant effects on the GNM and GN of three important grasslands in northern China, but changes their sensitivity to precipitation change. How the increase of extreme precipitation events will affect the soil nitrogen conversion process in terrestrial ecosystems in the future needs to be systematically studied over long time scales and large spatial patterns.

Aims In the salinized grassland of the agro-pastoral ecotone with limited nutrients, the increase of nitrogen input induced by agricultural fertilization and the change of land use patterns usually causes changes in soil available nutrients, which could further affect the net primary productivity of plants. However, due to the impact of annual precipitation, it is still uncertainty about whether the response of net primary productivity of plants to nitrogen addition and mowing varies with changes in rainfall.

Methods This study investigated plant net primary productivity under nitrogen addition and mowing at salinized grassland in the agro-pastoral ecotone of northern China, based on the experimental platform for nitrogen forms and mowing at the National Research Station of Grassland Ecosystems on the Loess Plateau in Youyu, Shanxi Province. There were six treatments including control and simulated nitrogen deposition experiments with two common nitrogen compounds (ammonium nitrate and urea), combined with and without mowing.

Important findings The results showed that: (1) Regardless of mowing or un-mowing treatments, short-term addition of ammonium nitrate and urea significantly increased the content of inorganic nitrogen in the soil, thereby increasing the aboveground (ANPP), belowground (BNPP), and total net primary productivity (NPP); (2) ANPP, BNPP, NPP, inorganic nitrogen content, and soil water content showed significant interannual differences, with higher values observed in the wet year (2018) than in the dry year (2017); (3) The interaction between short-term nitrogen addition and year had a significant impact on NPP. In the wet year, the positive effect of nitrogen addition on NPP was significantly higher than that in the dry year, which was mainly related to the synergistic effect of soil nitrogen and water; (4) Mowing decreased NPP and had a significant interactive effect with the year on the BNPP:ANPP. In the dry year, mowing generally decreased BNPP:ANPP. However, in the wet year, this negative effect gradually weakened and even turned into a positive effect. These results highlighted the crucial role of natural precipitation in regulating the response of net primary productivity of salinized grassland in the agro-pastoral ecotone to anthropogenic disturbances, and further indicated that the salinized grassland ecosystem in the agro-pastoral ecotone is jointly limited by nitrogen and water.

Aims Reseeding is one of the key measures for grassland restoration, and selecting reseeding species and their combination is crucial for the restoration effect. The key to grassland restoration is how to rationally combine multiple species to maximize functional complementarity and ensure community stability and multifunctionality.

Methods This study conducted a multi-species combination experiment of native grasses in a typical degraded alpine meadow in Maqu County, Gansu Province.

Important findings The results showed that multi-species reseeding significantly increased the biomass, coverage and species richness of the grassland. We comprehensively evaluated the indexes of aboveground biomass, species richness and proportion of high-quality forage in grassland after mixed reseeding different species combinations. Eventually, the combinations with better performance were screened out as: combinations based on grass mixtures: Elymus nutans + Festuca sinensis + Poa pratensis + Festuca rubra+ Poa crymophila + Puccinellia tenuiflora; combinations based on grass-legume mixes: Elymus nutans + Festuca sinensis + Poa pratensis+ Festuca rubra+ Tibetia himalaica + Medicago ruthenica and Elymus nutans + Festuca sinensis + Poa pratensis + Festuca rubra+ Tibetia himalaica + Medicago ruthenica + Vicia unijuga + Astragalus laxmannii; combinations based on grass-legume-sedge mixes: Elymus nutans + Festuca sinensis + Poa pratensis + Festuca rubra+ Tibetia himalaica + Medicago ruthenica + Vicia unijuga + Astragalus laxmannii +Cyperaceae. These multi-species mixing combinations maintained better community stability and grass production performance during the restoration of alpine degraded meadows in Gannan. This study can provide a reference for alpine grassland restoration in similar degraded areas.

Aims The influencing factors on the loss and accumulation of soil organic carbon in degraded grasslands need to be clarified. The lignin phenols derived from plant are important composition of soil organic carbon, and the decomposition of lignin phenols caused by benzene ring opening is an important process of soil organic carbon loss in degraded grasslands, however, studies on this point are not fully understood.

Methods Soil samples were collected in four degradation severities of typical grasslands in Xilin Gol, Nei Mongol. The content of lignin phenolic and the abundance of the key functional gene for benzene ring opening, catechol-1,2-dioxygenase gene (catA), and product (cis,cis-muconic acid) were measured. And variations of lignin phenols and the abundance of catA gene along the degradation gradient and their correlation with soil organic carbon content were also analyzed.

Important findings The results showed that 1) compared to the non-degraded grasslands, the content of lignin phenols in the soil of light, medium, and severe degraded grasslands decreased significantly, and showed a decreasing trend with increasing degradation. The content of lignin phenols showed the same pattern with significantly positively correlation with soil organic carbon content. 2) The abundance of catA gene significantly increased in degraded grasslands, and the abundance of its decomposition product cis,cis-muconic acid was significantly higher in moderate and severe degradation compared to that in the light and non-degradation grasslands. 3) The abundance of catA gene was significantly positively correlated with the abundance of cis,cis-muconic acid, while the content of lignin phenols was significantly negatively correlated with the abundance of catA gene. The abundance of catA gene and cis,cis-muconic acid were both significantly negatively correlated with soil organic carbon content. The results showed that, at the sample site scale, the decomposition of lignin phenols caused by benzene ring opening could be a potential mechanism in explaining the changes in soil organic carbon content in degraded typical grasslands in Nei Mongol. Thus, our results are expected to provide a new perspective for the driving mechanism of soil organic carbon loss and accumulation in degraded grasslands, and thereby providing a certain theoretical basis for the restoration of degraded grasslands.

Aims Grasslands provide many kinds of ecological services, including carbon sequestration, sand fixation, and biodiversity maintenance. However, some grasslands are experiencing degradation. To provide scientific theoretical support for grassland restoration, it is necessary to understand the limiting factors for vegetation restoration in degraded grasslands. In this study, we explored nutrient limiting factors for vegetation restoration under different degradation stages in typical steppe of Nei Mongol.

Methods Plant and soil samples were collected during August in 2021-2022, from 13 sampling sites (four plant communities under different degradation stages within each site: non-degradation, light degradation, moderate degradation, and heavy degradation) in typical steppe. We examined the effects of degradations on above-ground biomass, coverage, and density of plant communities. Soil organic carbon, nitrogen and phosphorus contents were measured. Multiple statistical analyses, including least squares regression analysis, redundancy analysis, and multiple linear regression analysis, were used to clarify the nutrient limiting factors for vegetation restoration in degraded grasslands.

Important findings Plant community above-ground biomass, coverage, and density, as well as the contents of soil organic carbon, total nitrogen, and available phosphorus significantly decreased with the intensification of degradation. Under the whole degradation sequence and adjacent degradation succession stages, soil nitrogen content was the most influential factor on plant community properties, while soil phosphorus content marginally affected the overall degradation sequence. These results indicate that soil nitrogen availability is the most important nutrient factor limiting vegetation restoration. Consequently, nitrogen fertilization should be concerned in the future restoration works.

Aims In China, the restoration of degraded grasslands is impeding the management of grasslands and their sustainable utilization. Soil nutrient deficiency is one of the main constraints for restoring degraded grassland. The essence of soil nutrient regulation is to restore the original dominant species, promote grassland productivity and the occupancy of high-quality forage in degraded grasslands, and meanwhile diminish the negative environmental effects caused by nutrient addition.

Methods Taking advantage of a restoration experiment carried out in a degraded grassland of Hulun Buir, in terms of the deficient soil nutrients, the limiting elements for plant growth and the nutrient specificity for different plant species, we developed soil nutrient regulation technique.

Important findings The key technical points are as follow: demand-based dosage, synergy of nitrogen and phosphorus, microelements supplemention, early-spring fertilization, deep fertilizaiton and strip operation. Soil nutrient regulation technique has broad prospects in application in Hulun Buir grassland, China. Improving the productive and ecological functions of degraded grasslands is of great significance for increasing the income of farmers and herders, ensuring the security of fodder grass supply, and safeguarding ecological security and national unity in northern China.

Aims The severe degradation of grassland ecosystems is restricting China’s ecological security and economic development, and this makes it a scientific and technological challenge for pastoral areas to effectively restore degraded grasslands. To date, multiple grazing management and human assisted improvement techniques have been developed, the implementation of these techniques played important roles in grassland restoration, but their effectiveness was constrained for degraded grasslands with severe damaged community structure and propagule shortage.

Methods We introduce a propagule regulation technique which can remove propagule limitation and target at restoring moderately and severely degraded grasslands. This technique includes two key technical aspects, namely, cultivation and transplantation of “propagule island”. The cultivation of “propagule island” is planting high-quality forage combining with nutrient management to promote the rapid growth of rhizomes (or lateral buds), i.e., cultivating “propagule island” with rich propagule pool (tiller rhizomes or branching buds). The transplantation of “propagule island” is replenishing the propagule pool to degraded grasslands, and restores grasslands relying on clonal growth (or asexual reproduction) of high-quality forage.

Important findings The main purpose of this technique is to rapidly restore the structure and function of communities in degraded grasslands taking the advantages of clonal growth of high-quality forage. According to the technical demonstration in the meadow grassland, “propagule island” of Leymus chinensis and Medicago falcatahad significant effects on restoration, and they increased the productivity of the two communities from 214.5 to 358.7 and 286.4 g·m^-2, respectively. They also increased the proportions of high-quality forage from 18.4% to 54.7% and 31.5%, respectively. This technique can provide important data and technical supports for the targeted restoration of propagule-restricted grasslands.

Aims The alpine meadows on the eastern Qingzang Plateau have degraded in some areas due to long-term overgrazing. As a crucial resource for degraded ecosystem restoration, the dynamics of soil seed banks and their role in degraded alpine meadow restoration remain unclear.

Methods We chose four different degradation levels of alpine meadows to construct a degradation gradient on the eastern Qingzang Plateau. We investigated the plant community and soil seed bank along the degraded gradient, explored the changes of plant community and seed bank along the degradation gradient, and analyzed the potential role of seed banks in alpine meadow regeneration and degraded alpine meadow restoration.

Important findings The results showed that: 1) the species richness and relative abundance of the plant community decreased significantly along the degradation gradient, but the species richness of the seed bank increased first and then decreased, and the seed density decreased significantly along the degraded gradient. 2) The similarity of species composition between the plant community and soil seed bank gradually increased with the degradation gradient, which suggests that the role of soil seed bank in plant community regeneration increased along the degraded gradient. 3) Compared with the plant community, there is a hysteresis response of the soil seed bank to alpine meadow degradation, which can buffer the influence of alpine meadow degradation on the plant community to a certain extent. Our findings indicated that the different responses of plant community and soil seed bank to degradation, and soil seed bank is crucial for the degraded alpine meadow restoration on the Qingzang Plateau. However, the potential role of the seed bank in the degraded alpine meadows restoration will be limited because of the depletion of seed bank resources at the seriously degraded level. These results can provide a scientific basis for the protection, restoration, and management of degraded alpine meadows on the Qingzang Plateau.

Aims Constructing multifunctional group species combination model is crucial for restoring severely degraded alpine grassland. However, the responses of multifunctional group species combination to severely degraded alpine meadows and relationship between plant diversity and ecosystem multifunctionality on the Qingzang Plateau remain unclear.

Methods In the study, we focused on the severely degraded alpine meadow at the Maqên County in the Sanjiangyuan Nature Reserve, and constructed four species combination models including grass mixture, grass + legume mixture, grass + legume + sedge mixture and grass + legume + forb mixture. The study evaluated the ecosystem multifunctionality under different species combination models by measuring plant diversity, primary productivity, and soil factors. Furthermore, the relationship between plant diversity and ecosystem multifunctionality was analyzed.

Important findings The results showed that: (1) Among the four species combination modes, the grass + legume + sedge mixture had the highest species richness and Shannon-Wiener index, whereas there was no significant differences in Simpson index and Pielou index between the multifunctional group species combination models. (2) The biomass increased significantly with the addition of plant functional group numbers, and was the highest in the grass + legume + sedge mixture. (3) Except for pH, conductivity, and available phosphorus content, all other indicators increased significantly under the grass + legume + sedge mixture. (4) Ecosystem multifunctionality was the highest under the grass + legume + sedge mixture, and the ecosystem multifunctionality showed decreasing pattern along with the increase of plant diversity. Our results indicated that the grass + legume + sedge mixture has a significant impact on promoting the recovery of soil nutrients and improving primary productivity in severely degraded alpine meadows. The study provides a multifunctional group species combination reference for the restoration of severely degraded alpine meadows in the Sanjiangyuan region, and is of great significance for promoting the theoretical development of ecological restoration in severely degraded alpine meadows on the Qingzang Plateau.

Aims The grassland dominated by Leymus chinensisis one of the most important grassland types in northern China, providing important ecosystem service functions. However, due to long-term irrational utilization, the nutrients in the ecosystem stay in a state where outputs exceed inputs, leading to widespread degradation of the current Leymus chinensis grassland. The degradation affects its ecological and production functions. Previous studies have shown that the coupling of livestock and poultry can promote the restoration of degraded grasslands. This study aims to clarify the impacts of the coupling of livestock and poultry on L. chinensis at the individual, population and community scales.

Methods This study compared the differences in the individual traits, population and community characteristics of L. chinensis in livestock and poultry coupled plots (LP), grass mowing plots (GM), and traditional cattle and sheep grazing plots (CS).

Important findings The results showed that the soil NO- 3-N content in LP was 2.5 to 3 times higher than in GM and CS, and the soil available phosphorus content was more than 2 times that of GM and more than 6 times that of CS. The increase in soil nutrients content significantly improved the individual traits and population characteristics of L. chinensis. The chlorophyll content, specific leaf area, nitrogen content and phosphorus content of L. chinensis leaves in LP were significantly higher than those in GM and CS. The important values of the L. chinensis population in LP significantly increased by 29.7% and 173.2% compared to GM and CS in the first year, respectively. The leaf area index of L. chinensis population in LP reached above 3.4, while GM remained around 1.0 and CS remained around 0.2. The aboveground biomass of L. chinensis population in LP increased to (431.5 ± 45.3) g·m^-2 in the second year, which was 1.6 times that of GM and 9 times that of CS. The development of the L. chinensis population promoted positive communities’ succession, with plant cover in LP reaching over 90%, significantly higher than GM (around 60%) and CS (approximately 40%). The aboveground biomass of the plant community in LP increased to (597.6 ± 61.3) g·m^-2 in the second year, close to twice that of GM and 3 times that of CS. Under the utilization of coupling livestock and poultry, chickens fertilize the degraded grassland with manure during the plant growing seasons, which promotes the individual growth and development of L. chinensis, thereby increasing the important value of the L. chinensis population, as well as enhancing plant community coverage and aboveground biomass, ultimately leading the degraded L. chinensis grasslands toward near-natural recovery.

Aims Most of the grasslands in the Sanjiangyuan area are degraded to varying degrees, and planting artificial grassland is an important measure to restore the ecological function of severely degraded grasslands. Moss crust affects soil nutrient cycling and the structure of microbial communities, so it is critical to investigate the feasibility of using moss crust to promote the restoration of degraded grasslands to understand the ecological role of bioconjugate crusts and develop reasonable and effective ecological restoration measures.

Methods In this study, four different grass combinations and three types of moss crust inoculation were set up to investigate the effects of moss crust inoculation on the soil microenvironment of artificial grassland in the “black soil beach” of Sanjiangyuan.

Important findings Moss crusts increased soil organic carbon, available phosphorus, ammonium nitrogen contents, and nitrate nitrogen contents, and available nutrients content were significantly higher in the artificial grassland than in the “black soil beach”. Actinobacteria, Proteobacteria, Acidobacteriota, Chloroflex, and Firmicutes were the top 5 dominant taxa in terms of mean relative abundance at the phylum level for bacteria, while Ascomycota, Basidiomycota, Mortierellomycota, unclassied_k_Fungi, and Olpidiomycota were the top 5 dominant taxa in terms of mean relative abundance at the phylum level for fungi. With the increase of moss crust inoculation, the number of bacterial operational taxonomic unit (OTUs) decreased and the number of fungal OTUs increased, and the moss crust inoculation did not significantly affect the microbial diversity index. The mixed-effects model results indicated that the moss crust significantly had a significant effect on the effective phosphorus, nitrate nitrogen, ammonium nitrogen contents, and microorganisms affecting their accumulation. Redundancy analysis shows that the bacterial community structure is susceptible to soil factors. Mantel test results showed that moss crust A1 (700 g·m^-2) inoculation had a significant effect on bacterial community composition than fungal community. Additionally, effective phosphorus, ammonium nitrogen, and nitrate nitrogen contents were positively correlated with the bacterial community. The above findings suggest that moss crust inoculation may affect soil nutrient accumulation and cycling by altering the microbial community environment, as well as promote the recovery of ecological function of the artificial grassland in Sanjiangyuan, providing a theoretical basis for future research into moss crust addition to restore the ecological function of soil in extremely degraded grassland.

Aims Leymus chinensis grassland is one of the most representative vegetation types in northern temperate grassland of China. Overgrazing causes great decline in the proportion of L. chinensis biomass to community biomass. Application of organic and inorganic fertilizers can significantly promote the recovery of L. chinensis population, but the underlying mechanisms are still poorly understood.

Methods In a degraded L. chinensis grassland in Hulun Buir, the effects of organic and inorganic fertilizers on plant community, L. chinensis populations and individuals were explored with the same amount of nitrogen (10 g·m^-2·a^-1) and phosphorus (3 g·m^-2·a^-1) application.

Important findings At the plant community level, the application of organic and inorganic fertilizers both consistently and significantly increased above-ground biomass in all three years (2021-2023), with the higher biomass under organic fertilizer application. While the application of organic fertilizer significantly reduced the species richness in the second and third year at community level. At the population level, both organic and inorganic fertilizers significantly increased the aboveground biomass of L. chinensis and its proportion in community-level biomass, with higher values under organic fertilizer application. In the third year, the density of L. chinensis with inorganic and organic fertilizer treatments significantly increased by 1.79 and 8.89 times, respectively. At the individual level, the biomass of L. chinensis with inorganic and organic fertilizer treatments significantly increased by 85.3% and 69.1%, respectively. Variance partition analysis suggested that the population density and individual biomass respectively explained 81.8% and 6.2% of the variation in population biomass of L. chinensis. Our results suggested that the application of organic or inorganic fertilizer can promote the restoration of degraded L. chinensis grassland. The increase in population density rather than individual biomass of L. chinensis is the predominant mechanism for its population recovery.

Aims Soil extracellular enzymes are crucial for soil organic matter decomposition and nutrient cycling. Soil enzyme activity and stoichiometry can provide insights into microbial resource limitations and soil nutrient availability. This study investigated the effects of grazing, particularly overgrazing that often leads to grassland degradation, on soil enzyme activity and stoichiometry, and identifies nutrient limitations in temperate grasslands.

Methods We conducted grazing experiments with varying stock rates in a typical steppe of Nei Mongol, and investigated the changes in the activities and stoichiometric ratios of soil extracellular enzymes. Enzyme activities related to carbon (C), nitrogen (N), and phosphorus (P) cycling were analyzed, and a vector model was applied to determine soil nutrient limitations under different grazing intensities.

Important findings 1) Soil hydrolase activities in the studied grassland ranged from 0 to 300 nmol·g^-1·h^-1, which is relatively low compared with the global averages. Grazing intensity significantly impacted the activities of soil enzymes, including α-glucosidase, cellulose hydrolysis, xylosidase, β-d-cellubiosidase, β-1,4-N-acetylamino-glucosidase, glycosaminidase, leucine aminopeptidase, and acid phosphatase. The enzyme activities peaked under moderate grazing and recommended grazing. 2) The Standardized Major Axis (SMA) regression analysis revealed strong linear relationships between the enzyme activities associated with C, N, and P cycling. The soil enzyme C:N:P stoichiometric ratio was 1:2.3:1.3, deviating from the global average 1:1:1. 3) The vector model based on soil enzyme stoichiometry indicated that the grasslands were co-limited by N and P, with P limitation becoming more pronounced as grazing intensity increased in Nei Mongol.

Aims Declining soil quality is one of the key limiting factors for recovery in moderately degraded alpine meadows. Furthermore, the irrational application of nitrogen and phosphorus fertilizers has a significant negative effect on the biodiversity of the Qingzang Plateau. However, there have been limited studies on the soil quality improvement techniques for moderately degraded alpine meadows on the Qingzang Plateau from a systematic perspective. The objective of this study was to investigate the effects of nitrogen and phosphorus fertilizers and microbial fertilizers on soil chemical properties and enzyme activities in moderately degraded alpine meadows.

Methods This study investigated the plant community characteristics, soil physicochemical properties and enzyme activities of different treatments under different treatments, including nitrogen and phosphorus fertilizers coupled with microbial fertilizers, in moderately degraded alpine meadows on the Qingzang Plateau.

Important findings The results indicated that both nitrogen and phosphorus fertilizers, when coupled with microbial fertilizers, significantly increased aboveground biomass. A significant interaction was observed in the effects on soil nutrient-related indexes, conductivity, and enzyme activities associated with carbon, nitrogen and phosphorus cycling. Overall, the application of both nitrogen and phosphorus fertilizers, in combination with microbial fertilizers, demonstrated clear restoration effects on moderately degraded alpine meadows. Microbial fungal fertilizers were found to enhance soil multifunctionality, and the combination of nitrogen, phosphorus, and microbial fertilizers yielded better results than the application of nitrogen and phosphorus fertilizers alone. The optimal physiological response was observed with the application of 45 kg·hm^-2nitrogen, 20 kg·hm^-2 phosphorus, and 225 kg·hm^-2microbial fertilizers. These findings provide a scientific basis for promoting the restoration of moderately degraded alpine degraded meadows on the Qingzang Plateau and enhancing ecosystem service functions.

Aims Plateau pika (Ochotona curzoniae) is a dominant small herbivorous mammal on the Qingzang Plateau, which affects the grassland ecosystem function through feeding, digging and excreting. Eimeriaspp., as the main intestinal parasite of plateau pika, has relatively high species specificity and is a potential new model for population control of plateau pika. However, it is still unclear about the change of plant communities in alpine grassland after control of plateau pika by Eimeriaspp.

Methods In this study, the grassland after control of plateau pika by Eimeria spp. and the control grassland were selected, and the plant diversity and network stability of alpine grassland after different treatments were analyzed to explore the effects of control of plateau pika by Eimeriaspp. on the plant community structure of grassland.

Important findings After field placement of Eimeriaspp., the active burrow entrance of plateau pika decreased significantly. After Eimeriaspp. treatment, grassland total coverage, Shannon-Wiener index, Simpson index and β diversity index increased significantly. The results of the mixed-effects model showed that Eimeriaspp. treatment had a greater impact on the Simpson index and Pielou evenness index. Increased inter-community correlations and average connectivity and stability in co-occurrence network analyses of plant communities after control of plateau pika by Eimeriaspp., and grassland keystone species changed from forbs to gramineae and cyperaceae. The results of this study provide new insights for biodiversity conservation, glires control, and ecosystem adaptive management of alpine grassland on the Qingzang Plateau.

Aims During the past decades, about a half of the global grasslands have been degraded as the results of climate change and anthropogenic activities. Grassland degradation substantially alters plant diversity and community composition; however, it remains elusive how these changes link to ecosystem productivity across broad geographic scales.

Methods Using a standardized survey from 45 grassland degradation sequences at 15 sites across three grassland types (i.e., alpine steppe, alpine meadow and alpine swamp meadow) on the Qingzang Plateau, we aim to explore changes in plant diversity and functional groups upon grassland degradation and their linkages with aboveground net primary productivity (ANPP).

Important findings Across the three grassland types, species richness, Shannon-Weiner diversity index, Simpson diversity index and Pielou evenness index all exhibited a first increase and then decrease pattern as degradation intensified. The coverage of sedge and grass declined, but legume coverage showed no significant changes and forb coverage increased along the degradation gradient. Mixed-effects models showed that degradation-induced change in ANPP was mainly associated with changes in coverage of original dominant species but minimally influenced by plant diversity for all grassland types. These results indicate that the degradation-induced productivity reduction is caused by the decline in dominant species rather than losses of plant diversity. The findings mentioned above provide important clues for alpine grassland restoration: restoring dominant species would be an effective approach for boosting ecosystem productivity in degraded grasslands on the Qingzang Plateau.

Aims China harbors extensive grassland resources, yet nearly 70% of these grasslands are afflicted by varying degrees of degradation under the combined pressure of climate change and human activities. Pinpointing the pivotal factors driving grassland degradation and establishing a rapid diagnostic system is imperative for precise condition assessments.

Methods This study was conducted in the Hulun Buir meadow steppe of Nei Mongol. The selected sites were categorized into four degradation levels: non-degraded, lightly degraded, moderately degraded, and heavily degraded. Vegetation and soil indicators were collected. Leveraging the random forests algorithm, degradation indicators were screened and weighted, with efforts made to reconcile ecosystem service priorities between the government and pastoralists.

Important findings This study identified ten key factors characterizing degradation, including aboveground biomass, proportion of high-quality forage, community height, litter biomass, species richness, leaf dry matter content, leaf thickness, soil density, soil water content and soil inorganic water content. These indicators encapsulate diverse ecosystem services, including forage supply, erosion control, biodiversity conservation, vegetation resilience, and water and nutrient regulation. Using non-degraded sites as a benchmark, a degradation index (DI) for the meadow steppes of Nei Mongol was developed, accompanied by delineated DI thresholds for different degradation levels. This study provides foundational data to support judicious selection of indicators for both national and regional standards.

Aims Seed coating is an effective measure to enhance seedling establishment and growth in extreme environment. Currently, seed coating is most commonly used in crops, this study designed multiple seed coating formulations to address poor field emergence and low establishment rates of major reseeding grass species on the Qingzang Plateau. Our work aims to providing technical support for efficient application of native grass species in restoring degraded alpine grasslands on the Qingzang Plateau.

Methods We designed multiple seed coating formulations using different levels of nutrients (N), microbial inoculants (MC), and growth regulators (G). We performed laboratory growth experiment and field experiments to evaluate the effects of different seed coating treatments on the seed emergence and growth of three grass species.

Important findings Emergence rates of Elymus nutans and Poa pratensis treated with microbial fertilizers + compound microbial inoculant + growth regulator (NMCG) were higher than those treated with other formulations. Such a formulation increased the emergence rates by 27% and 44% compared with the control (filler coating, CK3), respectively. Both the aboveground and belowground biomasses of Elymus nutans treated with microbial nutrients + microbial inoculant (NMC) were the highest. The above-ground biomasses of Festuca sinensis treated with compound microbial inoculant (MC2) were the highest, and the below-ground biomasses of Festuca sinensis treated with NMC were the highest. The above-ground and below-ground biomasses of Poa pratensis treated with NMCG were the highest. The field experiment showed grasslands reseeded with seeds treated using NMCG, they had the highest height, coverage, and above-ground/below-ground biomass. The restoration effects of other formula-coated reseeding were also better than those of grassland (CK1). Finally, all coating formulation containing microbial inoculants significantly increased the proportion of high-quality forage grass species in the restored grassland.

Aims The reed (Phragmites australis) is a long-rhizomed clonal plant, which is distributed worldwide and has the plasticity and adaptability to change its morphology, even growth form with environmental change. The creeping ramets of reeds are a special growth form generated from their rhizomes extending out of alkaline soil patches. This study aims to explore the growth of creeping ramets and their underlying mechanisms.

Methods Using methods such as regular tracking of ramet growth by hanging tags, measurement of photosynthetic physiology of leaves of different ages, and determination of ¹⁵N isotope transfer, we measured and analyzed the growth rhythms and patterns of creeping reed ramets, their photosynthetic characteristics, and indicators of physiological integration between ramets.

Important findings We found that in highly alkaline areas, reeds’ creeping ramets displayed different growth patterns compared to control, upright ramets. After 120 days of growth, the creeping ramets had an average length of (685.25 ± 118.75) cm, and their average growth rate during the observation period was (6.64 ± 3.51) cm·d^-1. This was 15.4 times faster than the control, upright ramets, indicating a logarithmic allometry growth process that started quickly but then slowed down. In contrast, the control ramets showed a relatively stable linear isogonic growth process. Young leaves at the top of the creeping ramets had the same maximum photosynthetic capacity as mature functional leaves. The net photosynthetic rate of leaves on the creeping ramets varied in a logistic curve with increasing leaf order, while the control ramets varied in a quadratic curve that first increased and then decreased. Moreover, the theoretical maximum net photosynthetic rate of creeping ramets was 19.4% higher than that of the control ramets. Creeping ramets treated with ¹⁵N isotopes had significantly higher levels of ¹⁵N abundance in various organs compared to untreated creeping ramets. Creeping ramets are a new adaptive feature of this widespread plant in extremely harsh alkaline habitat patches. The superior growth of creeping ramets is attributed to the high photosynthetic rate of young apical leaves and the physiological integration between tufted basal ramets and creeping ramets. This study provides new insights into the adaptation of reeds to extreme habitats and offers a method for analyzing the superior growth of creeping ramets based on matter production and physiological integration, with important theoretical implications.

Aims Understanding the adaptive strategies of plant root morphological traits and biomass allocation in alpine meadows under degradation is crucial for exploring the synergistic relationship between root morphological plasticity and biomass distribution. This knowledge is essential for deepening our insight into the stress tolerance strategies of plants in degraded alpine meadows.

Methods In this study, we investigated the aboveground and belowground biomass, root morphological traits, and their interrelationships in grasses (Poa pratensis and Elymus nutans), sedges (Carex alatauensis and C. moorcroftii), and forbs (Anemone rivularis and Saussurea nigrescens) across alpine meadows with varying degrees of degradation (nondegraded, lightly degraded, moderately degraded, and severely degraded).

Important findings The results show that: 1) Carex alatauensis exhibited the greatest reduction in aboveground biomass under moderate degradation (71.44%) while its root-to-shoot ratio increased the most under light degradation (216.92%) among all species examined. Both Poa pratensis and Anemone rivularis showed increased aboveground and belowground biomass under moderate degradation, and their root-to-shoot ratios showed no significant change with increasing degradation. The relative abundance of aboveground biomass in Anemone rivularis and the relative abundance of belowground biomass in Elymus nutans increased the most under severe degradation (384.90% and 299.57%, respectively). 2) Carex alatauensis showed the greatest decrease in total root length under severe degradation (72.81%), whereas Carex moorcroftii had the greatest increase in total root length under light degradation (14.81%). Degradation increased the average root diameter of Poa pratensis, Carex alatauensis, Carex moorcroftii, and Anemone rivularis while recuding their specific root length. The number of root tips and branching in Poa pratensis, Elymus nutans, Carex alatauensis, Anemone rivularis and Saussurea nigrescens decreased as degradation intensified. 3) The relative abundance of Poa pratensis belowground biomass was significantly correlated with the number of root tips. The relative abundance of belowground biomass in both Elymus nutans and Carex alatauensis depended on the total root length and the number of branching. For Carex moorcroftii, the relative abundance of aboveground biomass was mainly correlated with total root surface area, while the relative abundance of belowground biomass depended on root volume and specific root length. The relative abundance of aboveground biomass in both Anemone rivularis and Saussurea nigrescens was significantly associated with total root length, while their relative abundance of belowground biomass was influenced by specific root length. In conclusion, different dominant plant species adapt to the soil microenvironments caused by degradation by adjusting their biomass allocation and root morphological traits, and these adaptive strategies vary among species, reflecting the diversity of stress tolerance strategies in alpine meadow plants.

Aims Soil CH₄ and CO₂ fluxes, as key components of global carbon cycle, have a central role in mitigating and adapting to climate change. However, how soil CH₄ and CO₂ fluxes respond to climate warming and nitrogen (N) deposition during freeze-thaw cycles remain poorly understood.

Methods Here we investigated the effects of long-term (18 years) warming and N addition on soil CH₄ and CO₂ fluxes continuously during freeze-thaw cycles in a desert steppe of Nei Mongol used the SF-3500 multi-channel automatic soil gas flux measurement and control system from May 2021 to April 2022.

Important findings We found that warming, but not N addition, increased soil temperature. Warming and N addition did not change soil moisture. Annual cumulative CH₄ uptake flux ranged from 344 to 471 mg C·m^-2 in this desert steppe. Warming prolonged the duration of autumn freeze and increased soil cumulative CH₄ uptake flux, whereas N addition and warming plus N addition decreased CH₄ uptake during this period. On average, soil CH₄ uptake flux during the frozen winter period contributed to 8% of the annual total flux and no significant differences among different treatments. The contribution of soil CH₄ uptake during the spring thaw to annual total flux was 14%, and did not be changed by the warming and N addition treatments. Annual cumulative CO₂emission flux ranged from 101 to 106 g C·m^-2 in this desert steppe. Soil CO₂ emission flux during the autumn freeze period contributed most to non-growing season flux, and it tended to increase with warming and N addition. In particular, soil CO₂ flux shifted from emission to absorption during the frozen winter period. Both warming and warming plus N addition significantly increased CO₂ emission flux during the spring thaw. Overall, soil CO₂ flux during the non-growing season contributed to 9% of the annual total CO₂flux. Soil CH₄ absorption and soil CO₂emission were significantly correlated with soil temperature and moisture. Our results indicate that the desert steppe ecosystem acted as CH₄ uptake and CO₂ emission throughout the whole year, which help to understand the response, strength and direction of carbon source-sink under global change scenarios.

Leymus chinensis alliance, one of the most widely distributed communities in China’s temperate steppe, is a grassland vegetation type with the highest utilization value for animal husbandry. Investigating the distribution and community characteristics of Leymus chinensis formations can provide data for the management and restoration of natural grasslands. In this study, we investigated the characteristics of L. chinensis communities of 46 sites in Nei Mongol, including species composition, ecological characteristics, and community classification of L. chinensis alliance. A total of 187 vascular species, belonging to 109 genera and 37 families, were recorded. Asteraceae was the family with the most species, while Artemisia was the genus with the most species. Perennial herbs were the dominant life form, accounting for 71.66% of the total species. Xerophyte dominated the communities, accounting for 67.38% of the total species. The geographic composition of the system was dominated by the Eastern Palearctic species, followed by the Central Asian species. The L. chinensis alliance could be divided into 8 association groups, including Leymus chinensis - tussock, Leymus chinensis - semi-shrubby, Leymus chinensis - rhizome, Leymus chinensis - Carex, Leymus chinensis - annual/biennial, Shrub - Leymus chinensis, Leymus chinensis - bulbiferous herb and Leymus chinensis - forb and 26 associations.

Aims Plants and soil microorganisms play crucial roles in regulating the function and stability of terrestrial ecosystems. Exploring the variations in community composition and diversity of plants and soil microorganisms and their driving mechanisms along altitude gradients provides a better understanding of their responses to changes in terrestrial ecosystems and the mechanisms that maintain biodiversity under global change.

Methods In this study, a vertical gradient experiment was conducted across three grassland types on the northern slope of Kunlun Mountains. High-throughput sequencing was employed to assess soil bacterial and fungal communities. The study examined the patterns of variation in community structure, composition, and species diversity of plants and soil microorganisms along an altitudinal gradient (2 200-3 800 m) and explored their potential interrelationships.

Important findings The species diversity and productivity of plants, as well as the diversity of soil microorganisms (including bacteria and fungi) and soil nutrients content, all increased monotonically along the altitudinal gradient, with peak values observed in the alpine steppe. Soil fungi were more sensitive to environmental gradient than bacteria. The aboveground plant community and soil fungal community showed significant variation along the altitude gradient, while the structure and composition of the soil bacterial community remained largely unchanged. The species diversity and aboveground biomass of the plant community were significantly correlated with the diversity of the soil microbial community, with a stronger relationship observed with bacterial diversity than with fungal diversity. The species diversity of soil microorganisms and plants was positively correlated with mean annual precipitation (MAP) and soil carbon and nutrient (phosphorus and potassium) contents, but negatively correlated with mean annual air temperature (MAT). The pattern analysis showed that altitude (geographical distance) and climate factors had greater contributions to microbial and plant diversity than soil factors. The variation in climate factors (MAT and MAP) due to the altitude gradient was the dominant drivers of community dynamics in both plant and soil microorganisms, though their roles differed. Soil nutrients also played an important role in the diversity of both soil microorganisms and plants. In summary, the regional distribution pattern of aboveground plant and soil microbial communities in mountain steppe ecosystems is co-regulated by climate and soil factors associated with the altitude gradient in arid regions. This study highlights that climatic factors in arid areas are the dominant drivers of variations in the distribution pattern and structural composition of plant and soil microbial communities. Moreover, soil microbial diversity, especially bacterial diversity, plays a crucial role in enhancing grassland community productivity. The findings of this research provide valuable insights for grassland ecosystem management and biodiversity conservation in arid regions.

Aims The subalpine meadow of Wuyi Mountain is the highest meadows in the subtropical region of southeastern China. Identifying the variation characteristics of soil carbon flux components, and exploring their relationships with environmental factors and temperature sensitivity (Q₁₀) are of great significance for accurately estimating regional soil carbon balance and improving the knowledge about carbon flux dynamics in subalpine meadows.
Methods From May 2020 to April 2021, the LI-8100 CO₂ flux analyzer was utilized to systematically monitor the soil respiration rate (RS) in the meadow located at the summit of Wuyi Mountain. Additionally, the root exclusion method was applied to distinguish between the autotrophic respiration rate (RA) and heterotrophic respiration rate (RH).
Important findings (1) The dynamics of RS, RA and RH followed bimodal patterns, with consistently higher rates record from May to October compared to other months. Notably, the RA exhibited greater variability than RH throughout the year, accounting for 45% of RS. (2) A multi-model comparative analysis suggested that the temperature (T) exhibited an exponential correlation with soil respiration rate and its components in the subalpine meadow soil of Wuyi Mountain. The ranking of Q₁₀ values for soil respiration rate and its components was RA (Q₁₀ = 1.96) > RS (Q₁₀ = 1.94) > RH (Q₁₀ = 1.67). Although soil moisture (W) had a certain effect on RS, there was no significant relationship between RA and RH. The two-factor models including both T and W provided a better fit for RS than single-factor models, jointly explaining 48% of the variation in RS. In conclusion, soil respiration was primarily driven by heterotrophic respiration, while autotrophic respiration was more sensitive to temperature. Additionally, soil temperature and humidity were crucial environmental factors influencing soil respiration in the subalpine meadow of Wuyi Mountain, with soil respiration inhibited by low temperatures and high humidity. This study contributes to enhancing our understanding of the seasonal dynamics and influencing factors of soil respiration and its components in the subalpine meadow, providing valuable insights for regional soil carbon flux and carbon cycle research.

Aims This study primarily aims to investigate the spatiotemporal evolution patterns of fractional vegetation cover (FVC) in the grasslands of Xinjiang section of Tianshan Mountains over the period 2001 to 2020. It seeks to elucidate the determinants of these patterns, emphasizing the influence of vegetation types, livestock farming practices, precipitation levels, and mean annual air temperature. Ultimately, the goal is to contribute important insights that will inform decisions concerning the sustainable management and ecological conservation of these grasslands.

Methods The investigation into the spatiotemporal evolution patterns of vegetation in Xinjiang section of Tianshan Mountains and the factors influencing these patterns leveraged MODIS NDVI remote sensing data spanning two decades. A suite of analytical techniques, including Senʼs Slope Estimator + Mann-Kendall trend analysis, coefficients of variation, and land-use dynamics assessments, were employed to analyze the spatiotemporal variations in grassland FVC.

Important findings The study revealed a general stability in FVC, with the multi-year average varying between 0.33 and 0.42. Notable FVC increases were observed in the northeastern and southwestern low-altitude areas of the range, comprising 3.14% of the analysis area. In contrast, significant FVC declines were predominantly in the Ili River Basin, representing 15.81% of the area studied. The dynamics of grassland FVC were primarily driven by vegetation types and the total value of livestock farming output, each influencing over 29.85% of the variation. When considering the interaction with precipitation and mean annual air temperature, the influence of these factors on FVC increased to above 48.70%. Furthermore, a positive association between FVC and both annual precipitation and average annual temperature was noted, with areas displaying a correlation to precipitation covering 80.84% of the total area, largely encircling the basins flanking Tianshan Mountains range. Meanwhile, a correlation with mean annual air temperature spanned 71.69% of the area, predominantly at higher elevations. These findings offer valuable reference data to support strategic planning for the sustainable use and protection of grassland ecosystems in the Tianshan Mountainous region.

Aims Soil available nitrogen (N), generated from a series of soil mineralization processes, is a major limiting factor of terrestrial ecosystem productivity. Soil N availability depends on soil microorganisms, vegetation types, and soil physical and chemical properties. Soil microorganisms are very sensitive to environmental changes, especially the temperature change, which is closely related with microbial growth and reproduction. Therefore, it is important to understand the temperature sensitivity (Q₁₀) of microbial regulation of N mineralization rates in a large spatial scale for predicting the impacts of global climate changes on terrestrial ecosystem productivity.
Methods Three types of grasslands (namely meadow steppe, typical steppe, and desert steppe) were selected in Nei Mongol Plateau, Loess Plateau, and Qingzang Plateau, respectively. Soil net N mineralization rates were measured at different temperatures in the laboratory, and then Q₁₀ of N mineralization rates were calculated across different grassland types. Relative parameters, including soil microbe, soil physical and chemical properties, were also analyzed.
Important findings (1) The highest Q₁₀ of soil net N mineralization rates was found in all of three grassland types of Loess Plateau than those of Nei Mongol and Qingzang Plateaus. (2) The Q₁₀ values of soil net N mineralization rates in the meadow steppes and typical steppes on the Loess Plateau and Nei Mongol Plateau were significantly higher than those in the desert steppes, while on the Qingzang Plateau, the values in the alpine meadow steppes were significantly lower than that in the alpine typical steppes and alpine desert steppes. (3) Q₁₀ values of soil net N mineralization rates was closely correlated with soil microbial biomass carbon content across different grassland types. (4) The spatial pattern of Q₁₀ is jointly regulated by microorganisms, soil texture and substrate. The results of this study provide important data for understanding of the response of soil N cycle to global change in different grassland types in China, which is valuable for optimization of N cycle models of terrestrial ecosystems in the future.

Aims Soil organic carbon (C) pool plays an important role in regulating terrestrial C cycle and global climate, etc. The purpose of this study is to furnish data that will facilitate the scientific prediction of the C sink function of the grasslands in semi-arid regions under global change.

Methods Based on a two-factor field experiment of precipitation change (-50%, -30%, natural, +30%, +50%) and nitrogen (N) addition (0 and 5 g·m^-2·a^-1) established in 2017 in a desert steppe in Ningxia, we explored the response patterns and driving factors of soil organic C characteristics (content, storage, and components) in 0-60 cm soils after 4 years of treatments.

Important findings N addition had little effects on soil organic C characteristics. In contrast, precipitation exerted a significant influence on soil organic C characteristics, with the magnitude of the effect contingent up on the N level and soil depth. In the absence of N addition, both increasing and decreasing precipitation had a minimal impact on organic C characteristics across the whole 0-60 cm depth. In contrast, a 30% reduction in precipitation led to a significant increase in the content of easily oxidized organic C and dissolved organic C, while a 30% increase in precipitation resulted in a significant increase in the content of particulate organic C and light fraction organic C under 5 g·m^-2·a^-1 N addition. The content of soil organic C and its storage were positively correlated with soil water content, cellobiohydrolase activity and alkaline phosphatase activity. Conversely, they were negatively correlated with soil NO₃^--N. The content of easily oxidized organic C, particulate organic C and light fraction organic C was found to be positively correlated with soil leucine aminopeptidase activity and the Simpson dominance index, while negatively correlated with microbial biomass N content. Dissolved organic C and microbial biomass C content showed the opposite relationship with the three indices above. These findings indicate that alterations in precipitation levels exert minimal influence on soil organic C content and its storage in the context of N addition. However, moderate increases and decreases in precipitation will diminish soil organic C stability by influencing soil water content, N availability, enzyme activity and plant community dominance, which may, in turn, elevate the risk of soil C emission in desert steppes.

Aims Populations are the basis for the formation and development of the structure and function of grassland ecosystems. However, long-term grazing and global climate change like nitrogen addition profoundly impact the growth and reproduction of populations, such as Stipa bungeana, a dominant species in typical steppe of the Loess Plateau that has a high ecological and economic value. This study investigated how grazing and nitrogen addition affect the growth of S. bungeana.

Methods The study was based on a long-term rotational sheep grazing experiment in the typical steppe of the Loess Plateau. A completely randomized split-plot experimental design was employed, with stocking rate (0, 2.7, 5.3, 8.7 sheep·hm^-2) as the main factor and nitrogen addition levels (0, 5, 10, 20 g·m^-2) as the secondary factor. Morphological traits, aboveground biomass, the proportion of population biomass to total community aboveground biomass (PPB) and the relationship between them in S. bungeana were examined to investigate the effects of stocking rate, nitrogen addition and their interaction.

Important findings As the stocking rate increased, the plant height, canopy diameter, tiller density, seedlings, aboveground biomass, and PPB all followed a “single peak” curve trend, while the population density decreased. Nitrogen addition increased the plant height, canopy diameter, reproductive branch density, tiller density, aboveground biomass and PPB, while density of seedlings initially increased and then decreased as the nitrogen addition levels rose. The total effect of grazing on population aboveground biomass and the PPB was small compared with that of nitrogen addition. Specifically, grazing had a direct negative effect on aboveground biomass and affected PPB by regulating tiller density, population density and aboveground biomass. Nitrogen addition had a positive effect on aboveground biomass, both directly and indirectly through increasing plant height, reproductive branch density. It also impacted the PPB through regulating population density, canopy diameter, tiller density, and reproductive branch density. Overall, nitrogen addition increased canopy diameter and reproductive branch density and grazing increased density of seedings. The interaction of grazing and nitrogen addition significantly affected reproductive branch density. Stipa bungeana had maximum aboveground biomass or community status at a stocking rate of 4.10 or 5.29 sheep·hm^-2. These results indicated that grazing and nitrogen addition regulated the aboveground biomass and community status of S. bungeana through affecting its morphological characteristics, providing a basis for the scientific management and sustainable development of grassland populations.

Aims The management policies of China’s rangeland have shifted from grassland fencing and grazing removal towards a more balanced approach between livestock loads and herbage biomass for grazing. This shift has led to a growing emphasis on the theoretical and practical significance of using smart grazing management to promote grassland restoration.

Methods In this study, we conducted a two-year experiment involving continuous grazing, traditional rotational grazing, and intensive rotational grazing as treatment groups and no grazing as a control group to estimate the ecological and economic impacts of implementing intensive rotational grazing in a typical steppe of Xilin Gol.

Important findings Intensive rotational grazing could restore the biomass of Leymus chinensis and Stipa spp., and significantly put weight on the adult sheep. Furthermore, the advantage of intensive rotational grazing lies in extending the post-grazing recovery time and curbing selective animal grazing through balanced livestock loads and herbage biomass. Therefore, our preliminary results suggest that employing intensive rotational grazing and following balanced livestock loads and herbage biomass could be a promising approach to achieve a harmonious blend of economic benefits and ecosystem services in rangeland management practices.

Aims Aging is an important process in the life cycle of plants, and the capacity of different organs to store nutrients and their activities in plants are important in judging individual aging. To date, the changes in these aspects during the aging process of different age-class ramets in clonal plants remain unclear.

Methods Aster pekinensis is a typical clonal plant with a root sucker. On the grassland of Northeast China, its ramets are mainly composed of three age classes (1a, 2a and 3a). In this study, the differences in water soluble carbohydrates (WSC) contents among storage organs (stem base, root collar, and taproot) or among age classes, and the seasonal variation of rhythm in the three ramets of Aster pekinensispopulations were analyzed quantitatively.

Important findings At the yellow-leaf stage, the WSC content of the taproot was higher than that of the root collar. The WSC content of root collars and taproots in 1a and 2a ramets was significantly higher than that in 3a ramets. The WSC content of stem bases was significantly lower in 1a ramets than in 2a and 3a ramets. Throughout the entire growth season, the root collars of 1a ramets always received priority allocation of nutrients, and their WSC content continued to accumulate in an exponential form. The nutrient contents in the root collars of the 2a and 3a ramets, as well as the taproots of the three age-class ramets, were all consumed first and then accumulated, and the WSC content changed in the form of a quadratic curve. The capacity of the taproot to store nutrients was generally greater than that of the root collar, whereas the activity of the root collar was greater than that of the taproot across the three age-class ramets in Aster pekinensispopulations. The nutrient storage capacity and activity of young ramets were strongest. There were no signs of aging in adolescent ramets. The old ramets were dramatically aged, and their nutrient storage capacity and activity reduced significantly. This study provides a new approach that combines qualitative and quantitative analyses to understand the relationship between the spatiotemporal changes in WSC content and the aging process of individuals in plant populations.

Aims How nitrogen (N) addition impacts the emission of greenhouse gases (GHGs) is now becoming a hot issue in the study of global change. We aim to delineate the effects of N addition on the emission of major greenhouse gases (CO₂, CH₄and N₂O).

Methods In order to achieve this goal, the flux of the three major GHGs was measured using static chamber gas chromatography during the growing seasons (May through September) of 2020 and 2021 in a meadow steppe of Hulun Buir in Nei Mongol. The experiment was conducted by applying NH₄NO₃ to simulate the atmospheric N deposition, which involved six N addition levels (i.e., 0, 2, 5, 10, 20, 50 g·m^-2·a^-1) and two grassland utilization levels (i.e., mown and unmown).

Important findings The results showed that the response of the three GHGs to N addition showed clear nonlinear patterns, but there was a remarkable difference in the patterns among the three GHGs. The emission of CO₂ was increased with increasing N addition but saturated at around 10 g·m^-2·a^-1. The uptake of CH₄ was promoted with increasing N addition when N addition was low (0-5 g·m^-2·a^-1), but this promotion effect was diminished with further increase in N addition (5-10 g·m^-2·a^-1), and the uptake of CH₄ was inhibited when N addition reached 50 g·m^-2·a^-1. The emission of N₂O increased significantly with the increase of N addition rates, but the response patterns and amplitude showed remarkable difference between the two years. With the data in the two years pooled, the CO₂ flux had a significant positive correlation with precipitation and nitrate nitrogen (NO- 3-N) content, and a significant negative correlation with pH; CH₄ absorption flux was significantly positively correlated with precipitation and ammonium nitrogen (NH+ 4-N) content, while negatively correlated with pH; N₂O flux was significantly positively correlated with soil temperature and NH+ 4-N content, while significantly negatively correlated with NO- 3-N content. Our findings demonstrated that the response of the three GHGs to increasing atmospheric N deposition was largely nonlinear, and the response patterns were remarkably different among the three GHGs. These findings may be of great importance for controlling N fertilizer use, selecting appropriate grassland use, and evaluating grassland ecosystem warming potential under increasing atmospheric N deposition.

Aims Arbuscular mycorrhizal fungi (AMF) are widely distributed in grassland ecosystems. They make great contribution to the productivity and stability of grassland ecosystems. Our purpose was to explore the AMF community distribution characteristics and driving mechanism in grassland ecosystems.

Methods This study was conducted in 18 different grassland types. We demonstrate the AMF community characteristics and driving factors by investigating plant community characteristics, analyzing soil physicochemical properties and AMF communities.

Important findings In different grassland types, the dominant genera of AMF community were Claroideoglomus, Septoglomus, Diversispora, Rhizophagus, Acaulospora, Glomus and Ambispora. In addition, there exist significant differences in speicies composition and diversity of AMF communities, and the AMF diversity and rare operational taxonomic unites (OTUs) in Stipa purpurea grassland was relatively higher than those of other grassland types. Results from the structural equation model showed that AMF community diversity was significantly influenced by plant community diversity and soil pH, and AMF community composition was significantly influenced by temperature, soil moisture content and plant community composition. To sum up, abundant AMF resources were contained within Chinese natural grassland, and the AMF community characteristics in different grassland types are significantly different. Meanwhile, plant communities have remarkable driving effect on AMF communities in grassland ecosystems. So protecting grassland plant diversity is of great importance for maintaining soil microbial community stability.

For the universal grassland degradation and associated human utilization in the world, authors expound ecosystem restoration, climate climax in ecological succession, environment change and grassland state transition, grazing and disturbance climax, restoration by human intervention, thereby put forward the restoration path and state model of the degraded grassland ecosystem. This paper emphasizes that the restoration of degraded grassland should be carried out from the perspective of ecosystem, rather than only vegetation or soil processes, because there will be multiple alternative restoration states for grasslands in the context of environmental change or human disturbance. Three basic restoration modes of degraded grassland and possible restoration states are described as the followings: (1) Gradual restoration according to natural succession: based on the theory of ecological succession, grasslands from light to moderate degradation under favorable environments might reach the climax or near climax state for a long time by the systematical self-organization. (2) Intervention restoration by human activity: for those severely or extremely degraded grasslands, it needs to break through a series of abiotic (soil structure, nutrients, etc.) and biotic (plant colonization, species interaction, etc.) restrictions, and restore to a certain equilibrium or stable state, even climax state by using engineering, physical, chemical or biological-ecological methods or practices. It will take a long-time. (3) Restoration by grazing disturbance: grassland ecosystem structure (species composition and diversity), productivity and nutrient processes could be regulated through light to moderate livestock grazing, thereby maintaining and promoting grassland ecosystem multifunctionality and stability. This restoration method can be selected for medium-mild degraded grasslands. In conclusion, the holistic goal of grassland restoration is to achieve its long-term stable ecosystem multifunctionality.

Aims Both the carbon cycle and the function of grassland ecosystem as a carbon sink are impacted by the rising nitrogen deposition. Active organic carbon content is an important measure that can reveal changes in soil carbon pool. For a thorough understanding of carbon cycling and the creation of sensible ecosystem management strategies, it is essential to investigate the impacts of nitrogen addition on the active organic carbon fractions of grassland soils.

Methods Five different nitrogen addition treatments were set up in a temperate typical steppe of Nei Mongol. Soil organic carbon fractions content, soil physical and chemical properties, aggregate stability, microbial activities and extracellular enzyme activities were measured. Pearson correlation and structural equation model (SEM) were used to examine the relationships.

Important findings Nitrogen addition reduced the contents of dissolved organic carbon (DOC), microbial biomass carbon (MBC), and easily oxidizable organic carbon (EOC). The contents of DOC, MBC, and EOC all decreased with the increases of soil depth. The treatment of 5 g·m^-2·a^-1 nitrogen addition significantly promoted the decomposition of active organic carbon fractions. The effect of nitrogen addition on soil active organic carbon fractions content was regulated by biotic (microbial biomass, extracellular enzyme activity, etc.) and abiotic (soil physical and chemical properties, aggregate stability, etc.) factors. Nitrogen addition reduced soil density, increased mean mass diameter and the proportion of large aggregates, increased the contact between organic matter and substrate, promoted the decomposition of active organic carbon, and reduced the contents of DOC and EOC. Nitrogen addition inhibited the activities of polyphenol oxidase and peroxidase, reduced the decomposition of difficult-to-decompose organic matter and the contents of EOC and MBC. Nitrogen addition increased the activities of β-glucosidase and cellulose hydrolase, promoted the utilization of DOC by microorganisms, and reduced the content of DOC. Our results indicated that nitrogen addition treatment can affect the decomposition process of active organic carbon by changing soil physicochemical properties and the secretion of extracellular enzymes from microorganisms, promoting the release of carbon in grassland soils. This provided a theoretical basis for further exploration of grassland soil carbon dynamics under nutrient addition in the future.

Aims Soil respiration is one of the most critical components of carbon cycle in terrestrial ecosystems. The study on temporal dynamics of soil respiration and its linkage with environmental factors in desert steppes under changing precipitation can provide data supports for a deep understanding of the regulatory mechanisms of key carbon cycling processes in fragile ecosystems.
Methods A field experiment involving five precipitation treatments (50% reduction, 30% reduction, natural, 30% increase, 50% increase) was set up in 2014 in a desert steppe in Ningxia. The temporal dynamics of soil respiration rate were explored during the growing season (from June to October) in 2019, and the relationships between soil respiration rate and soil properties and plant characteristics were analyzed.
Important findings Soil respiration rate showed a seasonal variation of an increasing and a decreasing trend across the growing season, with the maximum values (2.79-5.35 μmol·m^-2·s^-1) occurring in late July or early August. Compared with the natural condition, 30% reduction in precipitation did not result in a significant effect on soil respiration rate, reflecting the adaptability of soil respiration to moderate drought. Overall, 50% reduction in precipitation reduced soil respiration rate, whereas increased precipitation (especially the 30% increase) enhanced soil respiration rate, and this positive effect was especially obvious in the early growing season (June to July). Soil respiration rate had a significantly exponential relationship with soil temperature and a significantly linear relationship with soil water content. Soil physicochemical property had a highly independent explanatory power for soil respiration rate (R² = 0.36), and its effect was highly correlated with soil biological property and plant diversity (R² = 0.31). Precipitation could affect soil respiration rate either directly or indirectly through the influences on soil biological property and plant biomass. The results indicated that a moderate increase in precipitation could accelerate soil respiration by alleviating soil water limitation, stimulating soil enzyme activity, promoting microbial activity and plant growth in the desert steppe, and that an extreme increase in precipitation would lead to a decrease in soil permeability and a hindrance to microbial metabolic activity, thus inhibiting soil respiration.

Aims Grazing, one of the primary ways of grassland utilization in Nei Mongol, has essential influences on plant community properties of grasslands. However, the comprehensive response patterns of Nei Mongol grassland plant community properties to grazing remain unclear.
Methods Based on a dataset derived from 76 studies, the plant community characteristics and soil physicochemical properties of Nei Mongol grasslands under different grazing intensities, different grassland types and different grazing years were integrated and analyzed in order to comprehensively evaluate the response patterns of Nei Mongol grasslands to grazing.
Important findings Our results showed that grazing significantly reduced plant above/below ground biomass, cover, height, density, species richness, Shannon-Wiener diversity index, Pielou evenness index, Simpson diversity index, and soil water content. The negative effects of grazing were strengthened with increasing of grazing intensity and duration. Moreover, grazing had a greater negative effect on the grasslands with sparse vegetation and low environmental carrying capacity (e.g., desert grasslands, sandy areas, etc.). This study shows that the responses of plant community characteristics to grazing in Nei Mongol grasslands are regulated by multiple factors, and appropriate grazing intensity and grazing time should be set according to different types of grasslands to achieve sustainable utilization of grasslands. The standards of grazing intensity in current grazing studies are not uniform, making it difficult to compare different studies, and the results from some studies do not have statistical significance due to a lack of replications in the experiment. The exploration of uniform quantitative standards for grazing intensity will be an important and challenging issue in future grazing studies, and the rationality of experimental design should also be emphasized.

Aims Grassland is an important component of terrestrial ecosystems around the world and plays an important role in terrestrial carbon cycling. However, large uncertainties still exist in predictions of soil organic carbon (SOC) dynamics in grassland ecosystems using earth system models, partly due to an inadequate understanding of the spatial patterns and drivers of soil carbon components and the rate of decomposition. In this study, we explored the determinants of the contents of total SOC and its components as well as the rate of soil carbon decomposition in the topsoil of temperate grasslands of Nei Mongol.
Methods Soil samples at depths of 0-10 cm were collected during July to August 2015 from field sites on the Nei Mongol Plateau. We measured the contents of total SOC and its partitioning in three soil aggregate size-classes, and the decomposition rate based on laboratory incubation. In addition, we acquired a suite of explanatory factors including climatic, edaphic, vegetation, and mineral variables. Variance partitioning analyses were then used to investigate the relative importance of the four factors in affecting the contents of total SOC, aggregate-classified carbon fractions and soil carbon decomposition rate.
Important findings The contents of total SOC and three carbon fractions displayed an increasing trend from southwest to northeast of the study area, while soil carbon decomposition rate (standardized by SOC) showed a reverse trend. The carbon contents in bulk soil and different aggregate fractions are highest in the meadow steppe, followed by the typical steppe and the desert steppe; whereas soil carbon decomposition rate (standardized by SOC) was highest in the desert steppe, followed by the typical steppe and the meadow steppe. The spatial variations of carbon contents in the three soil aggregate fractions were mainly driven by climatic and mineral factors, with finer soil particles attaching greater relative importance in the effect by the mineral factor. The soil carbon decomposition rate (standardized by SOC) was affected by mineral, edaphic, and climatic factors. These findings highlight the importance of considering the differential influences by minerals in different soil aggregate carbon fractions, particularly the silt- and clay-associated carbon in the Earth system models, so as to improve the accuracy in the prediction of SOC dynamics in grassland ecosystems under changing environment.

Aims Precipitation regime alteration and increasing nitrogen deposition have substantially altered the structure and function of grassland ecosystems. However, the responses of stoichiometry in soil and vegetation remain elusive, which limits the accuracy in predicting functional changes of alpine meadow.

Methods Based on a manipulation experiment platform of nitrogen addition (10 g·m^-2·a^-1) and precipitation change (precipitation reduction by 50% and increase by 50%) in an alpine meadow on the southern foot of Qilian Mountains, organic carbon (SOC), total nitrogen (SN), total phosphorus (SP) contents in topsoil (0-10 cm), and foliar carbon (LC), nitrogen (LN), phosphorus (LP) and potassium (LK) contents of dominant plant species, including Gentiana straminea, Elymus nutans, Oxytropis ochrocephalaand Kobresia humilis,were continuously surveyed from 2017 to 2020.

Important findings The soil stoichiometry varied significantly among different years, but was not affected by experimental treatments. The aboveground plant biomass showed inter-annual variations and was significantly affected by nitrogen addition. The responses of leaf stoichiometry were species-specific. Foliar stoichiometry of a resource-conservative species, E. nutans, showed limited variations, while that of the sensitive species, K. humilis, fluctuated significantly. To exclude the impacts of temporal variations, we conducted the analysis based on the relative changes (Δ) between treatment plots and the control plots from the same year and the results showed that nitrogen addition significantly increased ΔPB by 15.6%. Precipitation reduction significantly decreased ΔLC of O. ochrocephala by 6.8% while increased ΔLP of K. humilis by 19.8%. Our findings suggest that only nitrogen addition increased aboveground biomass and precipitation reduction altered LC and LP contents in some plant species. The temporal or species-specific effect, rather than experiment treatments effect, dominated the stoichiometric variations of soil and vegetation, highlighting the complex responses of alpine meadow to precipitation regime alteration and nitrogen addition.

Aims Physiological responses at the leaf level are determined by anatomical structure. Quantitative analysis of the responses of leaf anatomy to grazing in desert steppe is of great theoretical implications to reveal the ecological adaptation mechanism of plants to harsh environment.

Methods We measured 13 anatomical indices for leaves of Cleistogenes songorica, a dominant species in desert steppe under different grazing intensities, including control (CK), lightly grazing (LG), moderately grazing (MG), and heavy grazing (HG). Many indices measured were related to photosynthesis, including protective tissue, vascular tissue, and Kranz structure area. Comparative analysis for all the indices was made among different grazing intensities.

Important findings The results showed that: (1) cuticle thickness, as well as the ratio of cuticle thickness to leaf thickness first decreased and then increased with increasing grazing intensity. The thickness of motor cells decreases first and then increases with the increase of grazing intensity, compared with control and moderately heavy grazing areas, the thickness of motor cells in lightly grazing areas significantly decreased. (2) In terms of vascular tissue, the area of vascular bundle, vessel area, and phloem area were firstly increased and then decreased with the increases of grazing intensity. xylem area first decreased and then increased with the increases of grazing intensity. In terms of vascular tissue proportion, the ratio of xylem to vascular bundle area increased with the increases of grazing intensity, while the ratio between dominant vessel to vascular bundle area decreased with the increases of grazing intensity. The phloem area increased first and then decreased with the increases of grazing intensity. Compared with the control, phloem area significantly decreased in the three grazing treatments. (3) The area of Kranz structure increased with the increases of grazing intensity. Compared with that in the control, the area of Kranz structure was significantly increased in the three grazing treatments.