Contrasting Trends in Plant Diversity and Soil Carbon Mineralization Under Precipitation-Driven Vegetation and Soil Carbon Dynamics in the Mongolian Plateau.

Climatic shifts critically regulate soil organic carbon (SOC) dynamics, biodiversity, and productivity in grasslands. However, the mechanisms linking abiotic/biotic factors to plant diversity-SOC mineralization synergies remain unclear. To study this mechanistic relationship, we established 12 sampling sites along an east-west precipitation gradient across the China-Mongolia steppe. We measured plant diversity and biomass for both species and functional groups in 12 grassland sites. In the laboratory, we analyzed soil nutrients and microbial communities. We also measured the SOC mineralization potential using 28-day incubations. The results indicated that: (1) Aboveground biomass (AGB) increased through two opposing strategies, enhancing or reducing plant diversity, with thresholds at Shannon-Wiener indices of 1.14 (arid west) and 2.19 (humid east). AGB shifts altered resource competition and microenvironments, directly impacting diversity. (2) Plant diversity was primarily regulated by soil pH, SOC, and mean annual temperature (MAT). (3) Perennial grasses dominated productivity, while perennial forbs drove diversity via niche complementarity. (4) Microbial biomass carbon (MBC) was the direct driver of SOC mineralization, modulated by mean annual precipitation (MAP) through SOC mediation. (5) SOC mediated contrasting ecosystem effects by suppressing plant diversity through pH-driven nutrient limitations while simultaneously enhancing mineralization rates via stimulation of microbial decomposer activity. SOC properties and precipitation govern divergent changes in grassland diversity and carbon cycling. Strategic management of SOC pools, coupled with precipitation adaptation and biodiversity conservation, can enhance ecosystem resilience under climate change. This mechanistic framework advances understanding of grassland responses to global change.