Effects of Seasonal Rest Grazing on Soil Aggregate Stability and Organic Carbon in Alpine Grasslands in Northern Xizang

Abstract

Seasonal rest grazing is key to the recovery and sustainable use of alpine grasslands in northern Xizang. Postgrazing changes in soil structure and organic carbon stability are indicative of grassland recovery. However, the mechanisms by which seasonal rest grazing affects these soil properties remain unclear. This study examined alpine grasslands subjected to 5 years of seasonal rest grazing to assess its impact on plant community traits, soil aggregate stability, and the soil organic carbon content. The results show that (1) compared with traditional grazing, seasonal rest grazing significantly improved the height, coverage, undecomposed litterfall, and biomass of alpine grasslands while also substantially reducing the root–crown ratio. (2) Seasonal rest grazing resulted in a pronounced increase in the soil water content, whereas the soil bulk density, pH, soil organic carbon, total nitrogen content, and carbon–nitrogen ratio decreased. (3) Seasonal rest grazing enhanced aggregate stability and increased the proportion and organic carbon content of macro‐aggregate soil (> 0.25 mm), but the contents of micro‐aggregates (0.25–0.053 mm), silt + clay particles (< 0.053 mm), and their associated organic carbon decreased. (4) Redundancy analysis and structural equation modeling indicated that the effects of the soil organic carbon of each aggregate, physical properties, and chemical properties on the soil organic carbon content after seasonal rest grazing were more significant than those after traditional grazing and that macro‐aggregate soil organic carbon was the key factor affecting the soil organic carbon content. In conclusion, seasonal rest grazing can improve the productivity and soil organic carbon stability of alpine grasslands and plays an important role in alpine grassland ecosystem maintenance and organic carbon fixation, which is related to altitude.