Changes in soil organic carbon and its forms in recovering alpine meadows of various lengths in relation to altitude

Soil organic carbon (SOC) plays a crucial role in the global carbon cycle, but little is known about its changes (and its forms) in recovering patches of degraded alpine meadows of various lengths in relation to altitude. This study explores how altitude and the recovering period of patchily degraded meadow affect surface layer SOC and its forms in alpine meadow on the Qinghai-Tibet Plateau. The key pathways of environmental factors influencing SOC and its forms were determined via structural equation modeling (SEM). The results showed that SOC, light fraction organic carbon (LFOC), heavy fraction organic carbon (HFOC), dissolved organic carbon (DOC), easily oxidizable organic carbon (EOC) and particulate organic carbon (POC) exhibit negative correlations with elevation, whereas microbial biomass carbon (MBC) shows a positive correlation. SOC and its forms exhibit positive correlations with recovery length, SOC, LFOC, HFOC, DOC, MBC, EOC and POC increased by 20.67 %, 23.10 %, 20.64 %, 27.35 %, 36.98 %, 16.13 % and 33.62 % from 0.5 to 30 years. The content of SOC and its forms exhibited a significant downward trend (P < 0.05) with elevation in a shorter period of recovery, over which SOC became more sensitive to altitude. Individually, recovery length is more important to SOC variation than altitude, but only after a certain threshold. Altitude regulates SOC dynamics via multiple mechanistic pathways. SEM showed that recovery length had a direct positive effect on DOC, MBC, POC, TC, and SC (path coefficients of 0.823, 0.715, 0.489, 0.879, and 0.586, respectively). Elevation had direct negative effects on SOC, temperature and soil water content (path coefficients of −0.674, −0.639, −0.808, respectively), while exhibiting direct positive effects on POC and precipitation (path coefficients of 0.388 and 1.127, respectively). Secondly, through precipitation, elevation specifically influenced DOC and MBC. Additionally, elevation indirectly affected DOC, POC and MBC by influencing temperature and precipitation. The spatial distribution of SOC content is regulated by altitude and ecosystem factors such as vegetation characteristics and soil physicochemical properties during the recovery of degraded patches. Therefore, vegetation restoration and artificial precipitation enhancement should be prioritized in the rehabilitation of patchily degraded alpine meadows. This study provides a theoretical foundation for SOC management in alpine meadows, and recommends implementing differentiated restoration measures across various elevational zones.