Soil microbial community structure is an effective indicator to reflect changes in soil quality. Little is known about the effect of alpine meadow degradation on the soil bacterial and fungal community. In this study, we used the Illumina MiSeq sequencing method to analyze the microbial community structure of alpine meadow soil in five different degradation levels (i.e., non-degraded (ND), slightly degraded (LD), moderately degraded (MD), severely degraded (SD), and very severely degraded (VD)) in the Qinghai-Tibet Plateau. Proteobacteria, Actinobacteria, and Acidobacteria were the mainly bacterial phyla in meadow soil across all five degradation levels investigated. Basidiomycota was the mainly fungal phylum in ND; however, we found a shift from Basidiomycota to Ascomycota with an increase (severity) in degradation level. The overall proportion of Cortinariaceae exhibited high fungal variability, and reads were highest in ND (62.80%). Heatmaps of bacterial genera and fungal families showed a two-cluster sample division on a genus/family level: (1) an ND and LD group and (2) an SD, VD, and MD group. Redundancy analysis (RDA) showed that 79.7%and 71.3% of the variance in bacterial and fungal composition, respectively, could be explained by soil nutrient conditions (soil organic carbon, total nitrogen, and moisture) and plant properties (below-ground biomass). Our results indicate that meadow degradation affects both plant and soil properties and consequently drives changes in soil microbial community structure.

Alpine meadows on the Qinghai-Tibet Plateau constitute a critical pastoral production base in China. Nevertheless, these grasslands have experienced some degree of degradation, largely associated with the combined effects of climate change and anthropogenic activities. How grassland degradation relates to forage quality and carrying capacity, particularly from a nutritional perspective, remains insufficiently quantified. In this study, we investigated alpine meadows along a degradation gradient (non-degraded (ND), moderately degraded (MD), and severely degraded (SD)) in the Yangtze River source region. We measured forage yield and quality (crude protein (CP), acid detergent fiber (ADF), and crude fat (EE)) during both the peak growing and senescence periods, and calculated quantity, metabolizable energy, and digestible protein carrying capacity. The results demonstrated that (1) Community forage yield decreased by 38.56 and 55.14% during the peak growing period, and by 44.27 and 60.08% during the senescence period under MD and SD, respectively, relative to ND. (2) ADF and CP contents generally increased along the degradation gradient at both community and functional-group levels, whereas EE content declined. (3) All three carrying capacity metrics were substantially reduced under degradation; notably, metabolizable energy carrying capacity exhibited the largest relative decline during the senescence period (60.08% reduction under SD), suggesting that energy limitation becomes the primary nutritional constraint in degraded conditions. These findings provide quantitative evidence that grassland degradation diminishes not only forage quantity but also the nutritional base for livestock production. Among the metrics evaluated, metabolizable energy carrying capacity appears to be a more informative indicator for assessing grazing pressure in degraded alpine meadows than traditional yield-based estimates. We suggest that grazing management should consider degradation severity and prioritize energy-based carrying capacity thresholds, though these recommendations require further validation across broader spatial scales.