Contrasting soil C and N dynamics inferred from δ13C and δ15N values along a climatic gradient in southern China

Abstract

Secondary grasslands reestablished after deforestation in subtropical and tropical regions greatly alter terrestrial carbon (C) and nitrogen (N) dynamics and their associated ecosystem functions. However, reliable evaluations of C and N dynamics in secondary grasslands across regional climatic gradient remain challenging. We investigated natural 13C and 15N abundance in plants and soil as well as their associations with environmental factors (including climatic, plant and edaphic variables) from 20 sites across a 600 km climatic gradient in secondary grasslands of southern China. The δ13C values in plants and soil declined with increasing mean annual precipitation (MAP) but increased as the mean annual temperature (MAT) increased. These changes were mostly attributed to the shift in plant functional group between C4 and C3. In contrast, increasing MAP and decreasing MAT had positive effects on soil δ15N values, which were mainly related to changes in edaphic factors, including soil pH, soil C and N content and soil C:N ratios. Our findings indicate inverse patterns and different controls on soil δ13C and δ15N values along the climatic gradient, providing novel insights into the underlying mechanisms of ecosystem C and N dynamics in response to climate and vegetation change in secondary grasslands.