Impacts of land use change on soil carbon storage and phosphorus fractions in tropics

Human-induced land use transformations in tropical regions have notably impacted soil nutrient dynamics, particularly of carbon (C) and phosphorus (P). This study investigates soil C stocks and P fractions across six distinct land use types (fallow, residential, woodland, garden plots, cultivated lands, and grasslands) and their influence on soil P distribution at varying soil depths in Hainan Island, China. Higher concentrations of total carbon (TC) and soil organic carbon (SOC) were found in woodland (1.29 %, 1.21 %), garden plot (1.18 %, 1.1 %), and grassland (1.12 %, 1.02 %) soils at the topsoil (0–20 cm), with a noticeable decrease in deep soil layers (20–180 cm) compared to fallow, residential, and cultivated lands. In deeper soil layers (20–100 cm and 100–180 cm), woodland and grassland soils exhibited higher SOC and TC densities (10.09, 15.77 kg m⁻²; 15.29, 17.03 kg m⁻², respectively). Using Hedley’s modified Tiessen and Moir scheme, P fractionation analysis indicated P limitation in different land use systems. Grassland soils had higher organic P fractions (NaOH-Po, NaHCO₃-Po, HClc-Po) at 0–20 cm depth, remaining consistent at deeper layers. In cultivated and grassland soils, the inorganic P fraction (HCl_D-Pi) was the most significant contributor to total P across all depths. There was a steady trend in residual P across the land use depths. Correlations between labile (NaHCO₃-Pi, NaHCO₃-Po), moderately (NaOH-Po, NaOH-Pi, HCl_D-Pi) available P fractions and carbon stocks across all depths further revealed the crucial role of SOC in the regulation of P availability. It can thus be concluded that land use differentially influences SOC and P storage potential in Hainan Island, with divergence in soil layers. These findings highlight the significance of region-specific land management practices for maintaining soil health to mitigate climate change.