Vegetation restoration of abandoned cropland improves soil phosphorus availability and microbial activities in the Danxia degraded region

Abstract

Phosphorus is a limiting nutrient in subtropical region soils. The Danxia degraded region (DDR) is a typical ecologically degraded area in the south subtropical region of China, and mitigation measures for reconverting farmland to forest have been implemented to prevent further land degradation. However, whether vegetation restoration can alter soil P fractions (SPF) and P availability in the DDR remains unclear, and the mechanisms influencing P availability require further study. In this study, we collected soil samples from the main vegetation cover types, namely arbor forest, shrubland, and abandoned cropland, in the DDR to explore the characteristics of SPF, acid phosphatase (ACP), microbial community and their influencing factors. Results showed that vegetation restoration significantly affected soil P availability by modifying the SPF. Labile, moderately labile, and aggregate-occluded P content in the soil increased, whereas the proportion of stable P decreased. Vegetation restoration promoted the secretion of soil ACP and significantly increased the abundance of soil bacteria, fungi, actinomycetes, arbuscular mycorrhizal fungi, and the overall microbial abundance. Arbor forest soils presented higher SPF content and microbial activity than the soils from abandoned croplands and shrublands. This increases in soil microbial abundance was significantly correlated with soil microbial biomass and dissolved organic carbon. The results of redundancy and variance partitioning analyses indicated that soil nutrients and soil properties jointly drove SPF transformation in the DDR. Soil nutrient supply significantly affected soil microbial activity and SPF transformation. Vegetation restoration increased microbial activity by increasing the soil nutrient supply, and the resulting synergistic effect altered the SPF distribution and availability. This study provides a theoretical basis for the sustainable use of soil P resources in the DDR.