Response of Soil Carbon Mineralization to Grassland Management Practices on the Qinghai-Tibetan Plateau

Abstract

Grassland management practices strongly influence soil carbon dynamics, yet their effects on carbon mineralization processes in high-altitude regions remain poorly understood. We examined soil carbon mineralization patterns under four common grassland management practices implemented on the Qinghai-Tibetan Plateau (i.e., seasonal grazing, continuous grazing, perennial artificial grasslands, and annual artificial grasslands) using a 147-day incubation experiment. We also analyzed soil properties, microbial communities, and carbon degradation genes to understand the mechanisms driving carbon mineralization. We observed distinct depth-dependent responses to management practices. In surface soils (0–0.15 m), seasonal grazing exhibited the highest cumulative carbon mineralization (2993.32 mg CO₂-C kg⁻¹), 1.5-fold higher than annual artificial grasslands. However, in subsurface soils (0.15–0.30 m), continuous grazing showed the greatest cumulative carbon mineralization (2355.18 mg CO₂-C kg⁻¹), 1.5-fold higher than perennial artificial grasslands. Collectively, soil properties, carbon degradation genes, and fungal diversity explained 74% of the variation in cumulative carbon mineralization, with soil properties showing the strongest direct effect (path coefficient = 0.62). Interestingly, bacterial diversity exhibited a negative relationship with cumulative carbon mineralization, suggesting previously underappreciated mechanisms of carbon preservation involving microbial-derived compounds and their interaction with soil minerals. The variability in the abundance of specific carbon degradation genes across grassland management practices revealed that peroxidase and limonene 1,2-epoxide hydrolase genes showed positive correlations with cumulative carbon mineralization. Our results suggest that optimal soil carbon management in high-altitude grasslands is challenging and requires careful consideration of both grassland management practices and soil depth, especially spatial and temporal patterns of grazing pressure.