To identify salt-tolerant germplasm resources of Agropyron cristatum， this study subjected 31 germplasm samples to salt stress treatment with a soil salt content of 0.9%. Chlorophyll fluorescence parameters （phi2， NPQt， qL， Fv/Fm， Fo， Fm， Y（NPQ）， Y（NO）， and Y（II）） and physiological indicators （MDA， Pro， SS， and POD） were determined， and their salt tolerance was comprehensively evaluated using correlation analysis， principal component analysis （PCA）， and cluster analysis. The results showed that the coefficient of variation of the measured indicators of 31 samples ranged from 0.03 to 0.99. PCA indicated that the contribution rates of the top four principal components were 43.152%， 22.847%， 9.746%， and 8.882%， respectively. Cluster analysis suggested that the first group had higher photosynthetic efficiency and POD activity， and lower MDA content； the second group had moderate photosynthetic rate； the photosynthesis and physiological indices of the third group were severely affected. Based on PCA and cluster analysis， combined with changes in physiological responses， six salt-tolerant Agropyron germplasm （20-02， 20-03， 20-06， 20-08， 20-11， 20-17） were screened， most of which belonged to A. latissimum. In conclusion， the salt-tolerant germplasm obtained in this study could be used as the candidate materials for the breeding of new varieties of Agropyron， and also provide germplasm resources for the exploration of excellent salt-tolerant genes.

Based on the concept and practice of grassland livestock equivalent and “Standard sheep unit”， this paper defines the “Standard rodent unit” and explores its practical significance in grassland rodent survey， monitoring and pest control management. Referring to “Standard sheep unit” conception and the research progress of grassland rodents prevention and control in recent years， we analyzed the measurement indicators for relevant rodent standard unit and the methodologies for calculating rodents food equivalents. The definition of “Standard rodent unit” was as follows， based on the common weight of the average grassland rodents， one unit represents the daily loss caused by a 100 g rodent species consuming， cutting and storing 50 g fresh grass （about 50 % of its body weight）， which converts to 10 g of dry grass （assuming a moisture content of 20 %）. Eighty rodent units are equivalent to one standard sheep unit， with conversion of different rodents based on their weight differences. A preliminarily measurement relationship among “rodent-grass-livestock” at the level of forage intake was established， which will provide standard and basis for quantifying the foraging and food equivalents of different herbivores.

Shrub encroachment in grasslands， intensified by climate change and anthropogenic activities， represents a substantial threat to the health of grassland ecosystems. This underscores the pressing need for effective and precise biomass monitoring methodologies. The present study was carried out in the shrub-encroached grasslands of the Xilingol League， to investigate optimal above ground biomass （AGB） estimation model by utilizing unmanned aerial vehicle-based LiDAR and hyperspectral data validated against field measurements. Stepwise multiple linear regression， support vector machine， and random forest algorithms were employed for analysis. The results demonstrated a robust correlation between AGB and both LiDAR-derived mean canopy height and hyperspectral reflectance within the red-edge spectral region. Hyperspectral data demonstrated superior accuracy to LiDAR for herbaceous AGB inversion （R²=0.87 vs. 0.24）， whereas LiDAR performed better than hyperspectral data for shrub AGB inversion （R²=0.58 vs. 0.47）. Data fusion significantly improved the model performance， with the random forest model integrating features from both LiDAR and hyperspectral data achieving R² values of 0.88 and 0.64 for herbaceous and shrub AGB， respectively. The related findings offer critical scientific support for the sustainable utilization and precise management of shrub-encroached grasslands.

Microbial necromass carbon （MNC） constitutes a significant component of soil organic carbon （SOC） and plays a vital role in maintaining and enhancing carbon sequestration capacity of grassland ecosystems. The temperate grasslands of northern China represent a crucial component of global grassland ecosystems， but systematic understanding of their microbial necromass carbon content and its driving factors remains limited. To address this gap， this study established transects along a natural rainfall gradient from east to west in Inner Mongolia， covering three grassland types： meadow grassland， typical grassland， and desert grassland. Soil amino sugar content was measured using the biomarker method. By integrating climate and soil characteristics， the study systematically analyzed the distribution of soil microbial necromass carbon and its driving factors. Results indicate that the average microbial necromass carbon content in topsoil is 10.65 g·kg^-1， comprising 4.79 g·kg^-1 bacterial necromass carbon and 14.80 g·kg^-1 fungal necromass carbon. Structural equation modeling reveals that microbial necromass carbon is primarily regulated by annual mean temperature， dissolved organic carbon， and pH. These findings deepen our understanding of the distribution patterns and driving mechanisms of microbial necromass carbon in northern China's temperate grasslands， providing scientific support for regional grassland carbon management and enhancing soil carbon sequestration potential.

In order to screen out the germplasm resources of Medicago falcata L. with strong drought tolerance， 20 resources of M. falcata were selected in this study， and their drought tolerance was comprehensively evaluated by analyzing the changes in the content of morphological and physiological indexes of the seedlings， and by adopting the affiliation function method and cluster analysis.The results showed that under different drought stress treatments， all the 20 M. falcata germplasm resources showed different drought responses， as indicated by a downward trend in plant height， leaf area， survival rate， above ground biomass and chlorophyll fluorescence parameters. The drought resistance of the 20 M. falcata seedlings was classified into 7 categories by cluster analysis， among which， the material A2Z311 had extremely drought-resistant， and the material A2Z525 had the weakest drought-resistant. Based on the D value of the affiliation function， the drought resistance was ranked from strong to weak as A2Z311>A2Z588>A2Z355>A2Z600>A2Z317>A2Z480>A2Z423>A2Z534>A2Z528>A2Z316>A2Z350>A2Z436>A2Z302>A2Z491>A2Z351>A2Z594>A2Z599>A2Z622>A2Z353>A2Z525. The present study indicates that the material A2Z311 could better adapt to the treatment of drought stress， and the survival rate， leaf area and chlorophyll fluorescence parameters all being 1， showing stronger drought resistance， which provides a theoretical basis for the selection and breeding of alfalfa varieties in arid areas.

Seeds diffusion involving ants is a key link in the renewal of plant populations in desert ecosystems. Analyzing the interaction mechanisms between ants and plants is of great value for the conservation of endangered species. This study focused on Ephedra rhytidosperma， a plant species endemic to the Helan Mountains. Through field behavior observations （continuous tracking and recording for 3 days）， controlled experiments （removal treatment of aril， density gradients of 10， 20 and 30 individuals·m^-2） and combined with laboratory analysis， this study revealed the mechanism of action of Cataglyphis aenescens in the seeds dispersal of this species. The results showed that the peak of seeds transportation by Cataglyphis aenescens occurs from 10：00 to 11：00 in the morning， with an average transportation distance of 4.0 meters. The aril， due to its high nutritional content， has become a key factor affecting the transportation of Ephedra rhytidosperma seeds. The transportation quantity of Cataglyphis aenescens for the three different types of targets is as follows： intact seeds > aril > seeds with aril removed， and the transportation efficiency also decreases after aril removal. Cataglyphis aenescens shows bidirectional regulation in the transportation of seeds of different densities. High-density seeds are more likely to attract ants， but the removal rate is lower. This study revealed the nutritional reciprocity mechanism of Ephedra rhytidosperma seeds diffusion mediated by Cataglyphis aenescens， providing an important scientific basis for the recovery of endangered plant populations in desert ecosystems.

Soil nematodes are pivotal for material cycling and energy flow in grassland ecosystems. Clipping is a widespread grassland management practice in northern China. However， the mechanisms by which clipping affects the composition and structure of soil nematode communities remain unclear. nematode functional footprints across plant communities remain poorly understood. This experiment examined how clipping influenced soil nematode composition， structure， and functional footprint across six plant communities in the typical steppe of Inner Mongolia， providing a theoretical basis for grassland ecosystem management. Clipping significantly increased the total abundance of soil nematodes， the relative abundance of bacterivores， the maturity index， and the Wasilewska index. At the same time， it reduced the relative abundance of plant parasitic nematodes， the nutritional diversity index， the Shannon-Wiener index， the evenness index， and the enrichment index. Fauna analysis revealed that clipping increased the functional footprint of soil nematodes and food web complexity， while it reduced the enrichment index. Soil nematode community composition was significantly affected by soil nitrate nitrogen content， total carbon content， and litter mass. Our results demonstrated that clipping restructured nematode community composition， reducing plant parasitic nematodes’ abundance， thereby improving soil nutrient functions and promoting plant growth. This study concludes that clipping effectively maintains soil nematode community structure in typical steppe， offering a science-based framework for sustainable grassland management in northern China.

To screen cold-tolerant Medicago falcata germplasms and to clarify their physiological response mechanisms to low-temperature stress， this study systematically evaluated the physiological and chlorophyll fluorescence characteristics of 20 accessions under gradient low-temperature stresses （25℃， 10℃， 5℃， 0℃）. By measuring seven key indicators， it was found that the contents of malondialdehyde （MDA）， soluble sugar （SS）， and proline （Pro）， as well as the level of initial fluorescence （F_o）， exhibited upward trends with decreasing temperature， all significantly increasing at 0℃ （P<0.05）； while the relative chlorophyll content （Soil and plant analyzer development， SPAD）， maximum fluorescence （F_m）， and maximum photochemical efficiency of PSⅡ （Maximal photochemical efficiency of photosystem II， F_v/F_m） showed downward trends. A comprehensive evaluation using the membership function method combined with the standard deviation coefficient weighting method identified M₄， M₁， and M₁₀ as accessions with stronger cold tolerance. Stepwise regression analysis further established a cold tolerance prediction model （R²=0.932）， confirming F_v/F_m and SS content as critical evaluation indices. These results provide excellent germplasm resources and a theoretical basis for cold-tolerance breeding of alfalfa， and it is recommended that future research integrate omics technologies to further elucidate the underlying molecular regulatory networks.

To clarify the distribution characteristics of soil organic carbon （SOC） and its influencing factors under different grazing intensities in a typical Inner Mongolian grassland， this study measured and analyzed SOC， total carbon （STC）， total nitrogen （STN）， total phosphorus （STP）， soil water content （SWC）， soil pH， soil bulk density （SBD）， and aboveground biomass （AGB） across the 0-50 cm soil layers under no grazing （CK）， moderate grazing （MG）， and heavy grazing （HG） in Zhengxiangbai Banner， Xilingol League， Inner Mongolia. Key results included： SOC content decreased with soil depth under all grazing intensities， with the highest SOC content observed in the 0-10 cm layer. From 0 to 50 cm deep layers， SOC declined by 7% （CK）， 17% （MG）， and 8% （HG）. Moderate grazing significantly increased SOC content in the 0-30 cm layer， with the greatest increase （11%） in the 0-10 cm layer （from 35.33 to 39.45 g·kg^-1）. Grazing effects on SOC diminished with soil depth， showing weaker impacts on deeper layers.Grazing intensity altered SOC-environment relationships： SOC was primarily driven by AGB and SWC under CK， shifted to interactions with soil nutrients （STN） and physical properties （SBD， pH） under MG， and strongly correlated with STC， STN， STP， and SBD under HG. The study concludes that moderate grazing enhances SOC accumulation and transformation in the short term， while heavy grazing poses a risk of carbon loss despite no significant SOC reduction. Protecting surface carbon pools through controlled grazing intensity is critical for sustainable grassland management.

To investigate the effects of exogenous Melatonin （MT） on the growth and physiological characteristics of alfalfa （Medicago sativa） under low phosphorus stress， germplasms ‘7890’ and ‘15578’ were used as materials. The normal phosphorus （NP， 1.0 mmol·L^-1 KH₂PO₄） and low phosphorus （LP， 0.01 mmol·L^-1 KH₂PO₄） stresses were imposed by nutrient solution sand culture method. Five different concentrations of MT were applied to the roots of alfalfa seedlings under LP stress to determine their morphology and physiological indicators. The results show that： 90 μmol·L^-1 MT has the best effect in alleviating low phosphorus stress in alfalfa. The plant height， leaf area， aboveground and underground biomass， relative water content， root vitality， transpiration rate， stomatal conductance， net photosynthetic rate， contents of chlorophyll a， chlorophyll b， carotenoids， chlorophyll， proline， soluble sugar and soluble protein， as well as the activities of superoxide dismutase， peroxidase and catalase were all significantly increased. The concentrations of malondialdehyde and intercellular CO₂ were significantly reduced. Principal component analysis indicated that chlorophyll content， soluble sugar content， and leaf stomatal conductance could be used as key indicators for the growth and development of alfalfa under low phosphorus stress by MT. In conclusion， exogenous MT can enhance the activity of antioxidant enzymes and the content of osmotic regulatory substances in alfalfa seedlings under LP stress， and improve their tolerance to low phosphorus.