Soil nutrients, enzyme activities, and microbial communities differ among biocrust types and soil layers in a degraded karst ecosystem

Being different from the well-known and extensively researched counterparts in arid and semi-arid regions, biological soil crusts (BSCs) in degraded karst ecosystems with subtropical humid climate have been paid little attention. In this study, we investigated the differences of nutrient content, enzyme activity, and microbial communities between different types of BSCs (cyanobacterial crusts, moss crusts, moss-cyanobacteria mixed crusts, and bare soils), and between the BSCs layer and underlying soil. The results showed that the soil nutrient (total nitrogen [TN], total phosphorus [TP], and NH₄-N) contents and enzyme activity (urease) in the late-successional stage (moss crusts) were higher than those in early-successional stages (cyanobacterial crusts, moss-cyanobacteria mixed crusts, and bare soils). The species richness of the bacterial community increased with the succession of BSCs, but that of the fungal community did not change. The diversity and composition of both bacterial and fungal communities were not significantly different among biocrust types. The nutrient content (TN, NH₄-N), enzyme activity (urease, nitrate reductase, sucrase), and the richness of bacteria and fungi were significantly higher in BSCs layer than in subsurface soils. For either bacteria or fungi, there was a significant difference in community species composition but not in diversity between BSCs layer and subsurface soils. Besides, the results of network topological properties showed that the network structures of both bacteria and fungi in the BSCs layer were more complex than that in the subsurface, and positive links dominated both networks. These results indicate the importance of the BSCs layerespecially moss crusts for nutrient accumulation and microbial genetic resources, and provide an essential basis for further understanding the ecological functions ofBSCsin degraded karst ecosystems with subtropical humid climate.