Impacts of Two Land-Use Conversion Pathways on Soil Properties and Microbial Communities in Tropical Forests of Hainan Island

Large-scale tropical forest conversion to plantations or cropland severely impacts soil health. However, most studies have relied on pairwise designs, single-type chronosequences, or multi-type comparisons that are often confounded by environmental heterogeneity, thereby overlooking the complexity of successive land-use transitions on a common land-use background. Here, we investigated the responses of soil physicochemical properties and microbial communities to two conversion pathways (NSF → ORF → YRF; NSF → ORF → URF → AL) within a single farm, where shared soil parent material and climate allowed for a direct comparison of land-use types with different conversion pathways. Soil properties and microbial diversity were analyzed using physicochemical methods and high-throughput sequencing, with samples collected from five land-use types (six biological replicates per type). Results showed NSF had the highest soil properties. Along NSF → ORF → YRF, TOC, DOC, TN, IN and C/N declined gradually. In contrast, URF exhibited severe degradation, with AL showing partial recovery. Bacterial diversity remained relatively stable, whereas fungal communities were highly sensitive, with diversity decreasing progressively and dominant phyla shifting with intensified disturbance. DOC, EC and SM were most strongly associated with microbial community ordination, with pH showing no significant association. URF had the highest predicted abundance of C/N/S cycling genes, while NSF maintained a balanced fungal trophic structure. This study provides a comparative assessment of soil properties and microbial communities along two tropical land-use conversion pathways, contributing empirical evidence for sustainable land-use management in tropical regions.