Soil water retention modulates effects of soil nutrients and stoichiometry on stability of organic carbon in a karst region, Southwestern China

AimsThe inhomogeneity of bare rock distribution and the diversity of underground rock structure in different soil-rock microsites resulted in high soil heterogeneity. The aim of this study was to investigate the responses of soil nutrients and stoichiometry to soil-rock microsites and evaluate the relationship between soil substrate and SOC stabilityMethodsSix soil-rock microsite types were selected in a karst area of Southwest China, including rocky soil surface (RSS), stone crevice (SC), stone gully (SG), stone cave (SCA), stone pit (SP) and soil surface (SS). Soil samples were collected from 0-10, 10-20 and 20-30 cm depths, and three carbon fractions were isolated by combining flotation and screening.ResultsThe stocks of carbon (C), nitrogen (N), phosphorus (P) and sulfur (S) in the soil profile among different soil-rock microsites were in the order of SS > RSS > SG > SC > SCA > SP. SCA and SS contained the highest and lowest values of C, N, P and S densities, respectively. The N, P and S were positively correlated with LF/SOC and negatively with MF/SOC, stoichiometric ratios were also negatively with MF/SOC. Moreover, the saturation moisture content, capillary moisture capacity, and saturated hydraulic conductivity are important indicators that affect the SOC stability.ConclusionsThese results imply that soil-rock microsites regulate the stability of SOC by affecting the heterogeneity of soil nutrients and water, and the retention of soil water modulates the effects of soil nutrients and stoichiometry on the stability of SOC in karst areas.