Shifted Carbon Cycling Functions of Microbial Communities Along with Natural Restoration in Degraded Karst Areas

Soil carbon (C) cycling is mainly mediated by microorganisms. Natural restoration projects have been widely implemented in the degraded karst areas of southwest China. However, their impacts on the functional genes and microbial communities involved in soil C cycling have not been well recognized. In the present study, metagenomic sequencing was adopted to explore the functional genes and microorganisms involved in soil C cycling in three natural restoration stages (shrubbery, TG; secondary forest, SG; old growth forest, OG) in the southeast of Guizhou Province, China. The results indicated that natural restoration changed the composition of microbial genes involved in soil C cycling. When TG was restored into OG, the relative abundance of genes responsible for soil C decomposition increased, and that of the genes related to soil C biosynthesis increased first and then decreased. Correlation analysis and structural equation modeling revealed that plant diversity directly drove the changes of C biosynthesis-related genes (R = 0.50, p < 0.05); C decomposition-related genes were directly affected by both plant diversity (R = 0.43, p < 0.05) and soil nutrients (R = 0.34, p < 0.05). It was also found that Proteobacteria (31.87%–40.25%) and Actinobacteria (11.29%–26.07%) were the main contributors to soil C biosynthesis and C decomposition, but their contributions varied in three restoration stages. It can be concluded that natural restoration in degraded karst regions changed the C cycling functions of soil microbial communities by enhancing C decomposition potentials and first increasing and then decreasing C biosynthesis potentials. The results provide new insight into the regulation of soil C cycling during the restoration of degraded karst vegetation from genetic and microbial perspectives