First Author: ZHAO Tianqi
Corresponding Author: ZHANG Bin
Journal: Journal of Environmental Management

Abstract

Grazing exerts a significant influence on the accumulation of soil organic carbon (SOC) in grasslands. However, the relationship between SOC dynamics under different grazing intensities and changes in microbial necromass carbon (MNC) remains unclear.

In this study, a long-term continuous sheep grazing experiment was established in 2004 in the semi-arid steppe of Inner Mongolia, including a non-grazed control and multiple stocking rate treatments. After 17 years of grazing, soil samples were analyzed for physical, chemical, and microbial properties. Results showed that grazing reduced both SOC and MNC contents and the contribution of MNC to SOC.

Structural equation modeling (SEM) and enhanced regression analyses revealed that, with increasing grazing intensity, reduced plant carbon input led to a decline in MNC. Declines in plant carbon input, microbial abundance, and microbial diversity directly lowered MNC levels, which in turn decreased SOC content.

This study suggests that continuous heavy grazing likely reduces the contribution of MNC to SOC, though it may simultaneously enhance the cycling efficiency of grassland ecosystems. Maintaining low stocking rates helps preserve higher MNC and SOC contents, thereby contributing to grassland soil carbon sequestration and supporting the sustainable utilization of grassland resources.

Keywords: Nitrogen addition; Carbon sequestration; Semi-arid steppe; Microbial necromass; Stocking rate