Effects of different vegetation restoration on soil nutrients, enzyme activities, and microbial communities in degraded karst landscapes in southwest China

The karst area in southwestern China is one of the largest and continuous karst landforms in the world, and its ecosystem is highly sensitive and fragile. Appropriate vegetation restoration modes are of great significance for sustaining and improving the stability of the karst ecosystem, the dominant landform type in southwest China. Bacteria, linking soil and plants, play an important role in regulating the succession and restoration of karst vegetation. However, it remains unclear how soil bacterial communities and soil biochemical properties respond to vegetation restoration practices in karst areas. In this study, a 13-year long-term trial was performed using three planting restoration modes of deciduous broad-leaved, mixed evergreen and deciduous broad-leaved forest, and evergreen broad-leaved forests, with controls of natural enclosure. We aimed to investigate the impact of different vegetation restoration modes on the structure of soil microbial communities and their driving mechanisms using 16S rDNA Illumina sequencing, combined with the determination of 11 soil indicators and statistical models. The results showed that artificial restoration can improve soil nutrient contents, enzyme activities and microbial biomass more effectively than natural closure, which is beneficial to the rapid restoration of vegetation after abandoning of farmland. Among them, the effect of deciduous broad-leaved treatment on artificial restoration mode was better than that of mixed evergreen and deciduous broad-leaved forest and evergreen broad-leaved forest. In sequencing results, artificial restoration increased the relative abundance of Proteobacteria, but decreased that of Acidobacteria. In addition, pH, soil microbial biomass carbon, and urease activity significantly increased bacterial diversity. Different vegetation restoration measures significantly changed the soil bacterial community structure. The bacterial community of deciduous broad-leaved forest was the most beneficial to the benign development of soil. Mantel test showed that pH and soil microbial biomass carbon and nitrogen were the key driving factors of the soil bacterial community. FAPROTAX analysis showed a significant positive correlation between sucrase activity and phototrophy functional bacteria. The results demonstrated that compared with natural enclosure, artificial vegetation restoration promoted rapid community succession, and construction of deciduous broad-leaved forest was the most effective way to manage karst areas, improve soil nutrients, alter its key microbial populations, promote ecosystem services, and eventually benefit the restoration of vegetation in karst areas.