Influence of plateau pika disturbance on soil organic carbon in Zoige alpine grasslands — based on the role of soil aggregate

Soil aggregate plays a critical role in the sequestration of soil organic carbon (SOC) on the Qinghai-Tibetan Plateau (QTP). However, the impact of plateau pika (Ochotona curzoniae) on these processes remains uncertain. In this study, we examined both control and pika disturbed alpine grasslands across various degradation levels, including undegraded (UDM), lightly (LDM), moderately (MDM) and severely (SDM) degraded sites. Through analyzing variations in aggregate size distribution, stability, aggregate associated SOC (ASOC) and bulk SOC (BSOC) concentration, we investigated the influence of plateau pika disturbance on SOC, and compared these effects across varying degradation levels. The results indicate that: (ⅰ) pika disturbance decreases soil water content (SWC) by 26.3% and 22.2% in LDM and SDM at the surface soil layer, while increasing SWC by 34.1% and 30.4% in LDM and MDM at the subsurface soil layer. It significantly reduces bulk density (BD) across all soil depths and grassland types, with most significant effect in LDM; (ⅱ) Plateau pika disturbance increases the macroaggregate proportion in both dry-sieved aggregate (DSA) and water-stable aggregate (WSA), particularly in LDM. It enhances mean weight diameter (MWD) and geometric mean diameter (GMD) for both DSA and WSA, especially in MDM; (ⅲ) Pika disturbance mitigates the negative effect of soil properties on aggregate stability, particularly in LDM and MDM, thereby enhancing the positive effect of aggregate stability on ASOC and improving BSOC content, especially in LDM. These findings provide novel insights into the effects of plateau pika disturbance on SOC dynamics in alpine grasslands.