Abstract: Climate and grazing have a significant effect on vegetation structure and soil organic carbon (SOC) distribution, particularly in mountain ecosystems that are highly susceptible to climate change. However, we lack a systematic understanding of how vegetation structure reacts to long-term grazing disturbances, as well as the processes that influence SOC distribution. This study uses multiple sets of data spanning 20 years from a typical alpine grassland in the Qilian Mountains to investigate the effects of climate and grazing on various root-type grasses as well as the mechanisms that drive SOC distribution. We found that grazing increases the biomass of annual, biennial and perennial taproots while decreasing that of perennial rhizomes. We also found that various root-type grasses have different responses to climate and grazing. Multiple factors jointly control the variation of SOC content (SOCc), and the variation of SOC stock (SOCs) is mainly explained by the interaction between climate and grazing years. Climate and grazing can directly or indirectly affect SOCc through vegetation, and SOCs are mainly dominated by the direct effects of grazing years and grazing gradients. Grazing gradients and root-type grass biomass have a significant effect on SOC, with little effect from climate factors. Therefore, long-term grazing may affect the root-type grass and further affect SOC distribution through differences in nutrient acquisition ability and reproductive pathways. These findings provide important guidance for regulating soil carbon sequestration potential by varying the proportion of different root-type grass in the community via sowing, livestock configuration, or grazing time.

Key words: Alpine grassland, Climate factors, Grazing management, Soil organic carbon, Vegetation composition

摘要： Climate and grazing have a significant effect on vegetation structure and soil organic carbon (SOC) distribution, particularly in mountain ecosystems that are highly susceptible to climate change. However, we lack a systematic understanding of how vegetation structure reacts to long-term grazing disturbances, as well as the processes that influence SOC distribution. This study uses multiple sets of data spanning 20 years from a typical alpine grassland in the Qilian Mountains to investigate the effects of climate and grazing on various root-type grasses as well as the mechanisms that drive SOC distribution. We found that grazing increases the biomass of annual, biennial and perennial taproots while decreasing that of perennial rhizomes. We also found that various root-type grasses have different responses to climate and grazing. Multiple factors jointly control the variation of SOC content (SOCc), and the variation of SOC stock (SOCs) is mainly explained by the interaction between climate and grazing years. Climate and grazing can directly or indirectly affect SOCc through vegetation, and SOCs are mainly dominated by the direct effects of grazing years and grazing gradients. Grazing gradients and root-type grass biomass have a significant effect on SOC, with little effect from climate factors. Therefore, long-term grazing may affect the root-type grass and further affect SOC distribution through differences in nutrient acquisition ability and reproductive pathways. These findings provide important guidance for regulating soil carbon sequestration potential by varying the proportion of different root-type grass in the community via sowing, livestock configuration, or grazing time.

关键词: Alpine grassland, Climate factors, Grazing management, Soil organic carbon, Vegetation composition