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 (HClD-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, HClD-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.