Background Grassland ecosystems play a crucial role in maintaining biodiversity and supporting animal husbandry, yet degradation severely threatens these functions. The Xiwuzhumuqin meadow steppe in Inner Mongolia's semi-arid to arid ecotone experiences significant degradation from climate change and human activities. Understanding vegetation-soil feedback mechanisms in this typical region is essential for restoration strategies across northern China's vulnerable grasslands. This study systematically investigates relationships between plant community structure and soil properties across degradation gradients.

Methods Four degradation levels were surveyed: non-degraded (NDG), lightly degraded (LDG), moderately degraded (MDG), and severely degraded (SDG) grasslands. Vegetation characteristics (coverage, height, biomass, density, frequency) were documented. Soil samples (0-20 cm) were analyzed for bulk density, water content, pH, electrical conductivity, soil organic carbon (SOC), total nitrogen (TN), and total phosphorus (TP). Principal component analysis (PCA) and Pearson correlation analysis identified key drivers.

Results With intensifying degradation, plant community coverage, height, and biomass significantly decreased, showing a consistent pattern of NDG > LDG > MDG > SDG. Specifically, total coverage declined from 85.3% (NDG) to 72.6% (LDG), 58.4% (MDG), and 32.7% (SDG); average height decreased from 45.2 to 38.7, 29.3, and 18.6 cm; aboveground biomass dropped from 186.4 to 142.8, 95.6, and 48.3 g/m² respectively. Vegetation diversity indices differed significantly (P < 0.05) across degradation levels with varied patterns: the Shannon-Wiener index peaked at MDG (2.34), compared to NDG (2.08), LDG (2.28), and SDG (1.76); Simpson's index increased from 0.15 (NDG) to 0.38 (SDG). Soil bulk density increased progressively from 1.12 (NDG) to 1.25 (LDG), 1.36 (MDG), and 1.45 g/cm³ (SDG), while electrical conductivity rose from 86.4 to 102.5, 124.8, and 142.7 μS/cm. Conversely, soil water content declined from 18.6% to 15.2%, 12.4%, and 9.3%; pH decreased from 7.8 to 7.5, 7.1, and 6.9; SOC dropped from 21.4 to 17.6, 13.2, and 8.7 g/kg; TN decreased from 1.86 to 1.54, 1.12, and 0.73 g/kg; TP declined from 0.54 to 0.46, 0.35, and 0.28 g/kg across the degradation gradient. Correlation analysis revealed highly significant positive correlations (P < 0.01) between SOC, TN, TP, pH and vegetation coverage, biomass, height, and density, while no significant correlation was found with vegetation frequency. PCA identified soil nutrients as the primary driver of plant distribution, contributing 71.6% of the variance, forming a feedback mechanism of nutrient loss and vegetation degradation.

Conclusions This study reveals non-linear responses and feedback mechanisms within the vegetation-soil system during meadow steppe degradation. The diversity peak under moderate degradation provides scientific evidence for graded management and targeted restoration in semi-arid to arid ecotone grasslands.