Patterns of δ 13 C and δ 15 N in soil profiles under seasonally dry evergreen and deciduous tropical forests

Aims Evergreen and deciduous forests can coexist at different spatial scales in the seasonally dry tropics of Southeast Asia. At present, the main drivers for their differences in soil carbon (C) stock remains unclear. We aim to characterize the patterns of C and nitrogen (N) isotope ratios in soil profiles of two forest types to get a better understanding of how soil organic matter (SOM) pools are maintained under different types of forest ecosystem. Methods We analyzed the coupled trends in the natural abundances of C and N isotopes (δ 13 C and δ 15 N) in leaf litter, and mineral soil and its density fractions, collected from eight sites in Cambodian tropical forests. Results The mean value of the beta coefficient, which was calculated as the slope of the regression line for δ 13 C values against the logarithm of the C concentration and can serve as a natural indicator for SOM turnover, was − 1.9, while the Δ 15 N, which was the difference in δ 15 N between the leaf litter and mineral soil at 15 − 30 cm depth, was 6.2‰. Contrary to our expectations, these indexes did not differ significantly between evergreen and deciduous forest types. Conclusions The absence of clear difference in beta coefficients and Δ 15 N values between forest types was considered as derived from counteracting effects of several factors, e.g., tree biomass, precipitation and soil mineralogy, associated with multiple processes of C and N cycles. We especially highlighted the significant role of soil acidity in characterizing SOM cycles in seasonally dry tropical forests.