Land-use changes alter soil bacterial composition and diversity in tropical forest soil in China

Tropical forests, under pressure from human activities, are important reservoirs of biodiversity and regulators of global biogeochemical cycles. Land-use and management are influential drivers of environmental change and ecosystem sustainability. However, only limited studies have analysed the impacts of planting age and vegetation type under land-use change on soil microbial community in tropical forests simultaneously. Here, we assessed soil bacterial community composition and diversity under different land-use in Hainan Province, China, using high-throughput sequencing combined with PICRUSt analysis. Land-use included natural forest, 5-year-old crop-land, young (5-year-old) rubber tree plantation, and old (30-year-old) rubber tree plantation. Land-use changes altered the soil bacterial community composition but had a non-significant influence on alpha diversity (P>.05). We found that bacterial beta-diversity significantly decreased in young rubber tree plantation soils and cropland soils compared to natural forest as a control. In contrast, soil bacterial beta-diversity increased in old rubber tree plantation soils, indicating the effects of time since planting. There was no difference in microbial beta-diversity between soils from cropland and young rubber tree plantation. Soil bulk density and moisture, not pH, were the main environmental factors explaining the variability in microbial diversity. PICRUSt analysis of soil bacterial predicted gene abundances within metabolic pathways and indicated that land-use change altered soil functional traits, e.g., amino acid-related enzymes, ribosomes, DNA repair/recombination proteins and oxidative phosphorylation. Also, vegetation type, not planting age, had significant impacts on soil functional traits. Overall, planting age had the greatest influence on soil bacterial beta-diversity, while vegetation type was more crucial for soil functional traits (