Effects of vegetation succession on topsoil C, N, and P contents and stoichiometry following agricultural abandonment in a representative karst trough valley

Abstract

Soil carbon (C), nitrogen (N), and phosphorus (P) are significantly altered by vegetation succession under execution of ecological restoration projects in China. However, the changes in soil C, N, and P contents and their molar ratios as affected by vegetation succession are elusive in fragile karst ecosystems. With space-for-time substitution, this study compared the soil C, N, and P contents and their molar ratios between different vegetation successional stages in a representative karst trough valley, Southwest China. Soil samples from four positive vegetation successional stages, including herb stage (HE), hern-shrub stage (HES), shrub stage (SH), and secondary forest stage (SF), were collected to determine the topsoil C, N, and P contents and molar ratios, and selected soil physicochemical properties. The results showed that soil C and N contents increased by 158.4% and 39.6% from HE to SF, respectively, while soil P content was not significantly affected by vegetation succession. From HE to SF, soil C:N and C:P ratios increased by 82.1% and 134.2%, but soil N:P ratio vary insignificantly, respectively. Soil bulk density (BD) and pH increased but electrical conductivity (EC) decreased markedly from HE to SF. Soil exchangeable K+, Ca2+, and Mg2+ contents did not differ among four successional stages. Soil pH, BD and exchangeable K+ were closely correlated with C and P contents, C:P, and N:P in different successional stages. Our results imply that vegetation succession driven by ecological restoration considerably increases topsoil C and N accumulations but equalizes P in the karst trough valley.