Soil organic carbon (SOC) plays a critical role in global carbon cycling and climate regulation, particularly in high-altitude permafrost regions. However, the impact of altitudinal gradients of alpine shrubs on SOC fractions remains poorly understood. In this study, we evaluated the rhizosphere SOC fractions and microbial biomass of Potentilla parvifolia along an altitudinal gradient (3,204, 3,350, 3,550, and 3,650 m). Our findings revealed that P. parvifolia significantly increased gram-positive bacterial and fungal biomass at medium and low altitudes (3,204, 3,350, and 3,550 m), enhancing the contribution of mineral-associated organic carbon (MAOC) to total SOC compared to bare soil. Moreover, SOC accumulation was primarily driven by the buildup of microbial necromass carbon, particularly fungal necromass carbon, within the MAOC fraction. These results improve our understanding of how altitudinal gradients influence SOC dynamics and microbial mechanisms, providing a scientific basis for developing effective bioprotection strategies to conserve high-altitude ecosystems under global climate change.IMPORTANCEThis study addresses critical knowledge gaps in understanding how altitudinal variation of shrubs affects soil carbon dynamics in the Qilian Mountains' seasonal permafrost. Investigating the redistribution between particulate organic carbon and mineral-associated organic carbon, along with microbial necromass (fungal vs bacterial), is vital for predicting alpine carbon-climate feedbacks. Shrub encroachment into higher elevations may alter vegetation-derived carbon inputs and decomposition pathways, potentially destabilizing historically protected permafrost carbon stocks. The unique freeze-thaw cycles in seasonal permafrost likely modulate microbial processing of necromass into stable carbon pools, a mechanism poorly understood in cold biomes. By elucidating altitude-dependent shifts in carbon fractions and microbial legacy effects, this research provides mechanistic insights into vegetation-mediated carbon sequestration under climate change. Findings will inform models predicting permafrost carbon vulnerability and guide alpine ecosystem management strategies in this climate-sensitive headwater region critical for downstream water security.

PurposeThe ecological damage caused by cut slopes in mountainous areas is serious, and ecological restoration is urgently needed. In this context, outside soil spray seeding (OSSS) combined with a frame beam is often used in mountainous areas of southwestern China. The aims of this study were (1) to determine the differences in soil organic carbon (SOC) and its fractions of cut slopes under different restoration methods and (2) to explore the factors influencing SOC and its fractions of cut slopes in this study area.Materials and methodsTwo cut slopes restored by different restoration methods (framed slope, using OSSS combined with a frame beam, FS; rimless slope, unassisted restoration, RS) were selected, and a nearby naturally developed slope that had not been cut was used as a reference (NS). The SOC, SOC fractions, and related soil parameters were investigated.Results and discussionCompared with RS, the available phosphorus, urease activity, amylase activity, microbial biomass carbon (MBC), and light-fraction organic carbon (LFOC) levels of FS were significantly higher. However, there were no significant differences in pH, bulk density, available nitrogen, saccharase activity, SOC, particulate organic carbon (POC), and readily oxidizable organic carbon (ROC) between FS and RS. Notably, the MBC contents of FS and RS were higher compared to that of NS, which may be due to the fact that the deep soil was exposed to the air after stripping the surface soil of the cut slopes, which facilitated the growth of aerobic microorganisms. The dissolved organic carbon (DOC) content of FS was lower than that of RS, most likely because of the higher MBC content of FS compared with RS. The main soil parameters influencing soil SOC and its fractions were available nitrogen, available phosphorus, and bulk density.ConclusionsDespite the implementation of ecological restoration measures, the SOC and its fractions of the cut slope did not fully recover, and there was a gap between the soil quality of FS and NS. Further research is needed to determine whether OSSS combined with frame beams is an effective ecological restoration method for cut slopes in this area.