Dual Isotopes Tracing Carbon and Nitrogen Dynamics during Leguminous and Non-Leguminous Litter Decomposition under Controlled Precipitation

Abstract

Plant litter decomposition figures importantly in the cycling of C and N pools in terrestrial ecosystems. We investigated how C and N fluxes changed during the decomposition of leguminous and non-leguminous leaf litters, and how these processes responded to different precipitation regimes. We used the dual-isotope tracing method to investigate differences in leaf and soil C and N, along with δ13C and δ15N, in the soil of the Loess Plateau in China. The δ15N and δ13C values were 3604‰ and 56‰ for Robinia pseudoacacia (Leguminosae) and 8115‰ and 452‰ for Populus tomentosa (Salicaceae) leaf litters. Through decomposition, δ13C decreased in all litters, and δ15N in the leguminous litter increased while it decreased in the non-leguminous litter. In the surface soil, the fraction of litter-derived N (14%) from the leguminous litter was significantly higher than that of the non-leguminous litter after 16 months. The C and N concentrations of both litters and soil always had a positive correlation during decomposition, and the responses of N to C changes in soil were reduced by the litter cover. Increased precipitation enhanced the litters’ C and N correlation. The 600 mm precipitation treatment most benefited litter C’s transformation to SOC, and drought conditions promoted the transformation of legume litter N to soil TN, but inhibited non-legume litter N. In the soil and both litters, C and N changes always had a positive correlation. After 16 months, the proportion of soil N from legumes was higher than that from non-legumes. Reduced precipitation could promote leguminous N in soil. Our results provide a scientific basis for accurately predicting the C and N cycles in terrestrial ecosystems.