Responses of soil labile organic carbon fractions and enzyme activity in Kubuqi Desert to different vegetation restoration measures

Vegetation restoration is a key strategy for reversing desertification and restoring ecosystem functions in drylands. However, its effects on soil labile organic carbon fractions, enzyme activity, and carbon pool stability in desertified areas are still largely unclear. This study focused on three typical artificial vegetation restoration measures in the Kubuqi Desert— Caragana korshinskii shrubs (NT), Salix psammophila shrubs (SL), and Corethrodendron fruticosum shrubs (YC)—alongside mobile sandy land. Combining field surveys and laboratory analyses, we investigated the distribution and dynamics of soil organic carbon (SOC) and its labile fractions (MBC: microbial biomass carbon, DOC: dissolved organic carbon, EOC: easily oxidizable organic carbon, LFOC: light-fraction organic carbon). We also examined the response of soil physicochemical properties and key enzyme activities, to clarify their interrelationships. Vegetation restoration measures significantly increased SOC content and storage, with NT showing the strongest effect, followed by SL and YC. Vegetation restoration measures also markedly altered the distribution of soil labile organic carbon fractions. NT significantly enhanced all measured labile carbon fractions, while YC notably increased EOC content and SL also markedly boosted LFOC. In addition, NT and SL reduced the proportion of labile carbon relative to the total SOC, indicating improved carbon pool stability. Restoration effects were pronounced in the 0–40 cm soil layer but limited at a depth of 40–60 cm. NT and SL significantly enhanced the activity of β-1, 4-glucosidase (BG), cellulobiose hydrolase (CBH), sucrase (SUC) and polyphenol oxidase (PPO), whereas YC only significantly increased SUC. Soil total nitrogen, total phosphorus, and enzyme activities were strongly correlated with labile carbon fractions and the carbon pool management index. Path analysis indicated that vegetation restoration promotes carbon transformation and sequestration by improving soil nutrient conditions and activating hydrolytic and oxidative enzyme systems. These measures drive a synergistic mechanism linking nutrients, enzymes, and carbon pools, with soil enzyme activity serving as a key indicator of carbon pool quality improvement. This study provides scientific basis for optimizing vegetation restoration strategies in desertification management and holds significant implications for assessing the soil carbon sequestration potential of ecological restoration.