Effects of biological soil crusts on soil labile organic carbon of patchy alpine meadows in the Source Zone of the Yellow River, West China

•BSCs is superior to the vascular vegetation in degraded meadow patches, especially restoring LOC, TN and SOM in soil.•Altitude and soil depth significantly reduced the content of LOC in soil.•BSCs promote the restoration of soil LOC by increasing soil TN content. Biological soil crusts (BSCs) play an important ecological role in the biogeochemical cycles, but there is limited knowledge about their effects on the composition of soil labile organic carbon (LOC) in the soil of patchy alpine meadow. In patchy alpine meadow with different altitudes, the different LOC compartments, vegetation, soil properties and C-hydrolase activity of active patches (with plateau pika), inactive patches (without plateau pika), restored patches, BSCs patches, and healthy alpine meadow were analyzed to assess the effects of BSCs on LOC. The key influence pathway of eco-environmental factors of LOC was determined by the structural equation model (SEM). The results showed that the BSCs at the altitude of 3570 m increased dissolved organic carbon (DOC), easily oxidized organic carbon (EOC) and microbial carbon (MBC) by 293%, 73% and 36%, respectively, compared with active patches in the 0–2 cm layer, which was significantly higher than those of inactive patches and recovered patches. There was no significant difference among DOC, EOC and MBC in different patches at the altitude of 4224 m. The MBC content of active patches decreased, but other patches and healthy alpine meadow showed a Λ- shaped change with altitude. The contents of soil total nitrogen and organic matter of BSCs patches were generally higher than those of active and inactive patches at three different altitudes. Structural equation model results showed that at the altitude of 3570 m, total nitrogen had a strong positive correlation with DOC, with a path coefficient of 0.677. There was a direct negative relationship between soil organic matter and DOC (path coefficient = −0.278) at the altitude of 4013 m. At the altitude of 4224 m, there was no direct correlation among soil nutrient, C-hydrolase activity, and soil LOC. Therefore, BSCs mainly promote the accumulation and recovery of LOC by increasing the soil total nitrogen content in different patches at different altitudes, which are beneficial to the restorations of LOC, total nitrogen and soil organic matter. Hence, they should be considered as key factors in the processes of restoring patchy alpine meadows.