Stable isotopic signatures of carbon and nitrogen in soil aggregates following the conversion of natural forests to managed plantations in eastern China

Abstract

Land cover change (LCC) from natural forest (NF) to plantations (PF) has occurred worldwide over the past several decades. However, the different LCC effects on soil aggregate C and N turnover in various climatic zones remain uncertain. Soil samples were taken from both NF and PF at five sites along an approximately 4200 km north-south transect in eastern China. We measured soil aggregate C and N concentrations, and δ13C and δ15N. The soil aggregate distribution is similar between NF and PF, except that the mass proportion of microaggregate is lower in NF. The impacts of LCC on soil C and N concentrations, and δ13C and δ15N vary among five climate zones. The changes in soil aggregate C and N concentrations and δ15N induced by LCC show nonlinear relationships with climatic factors (i.e., MAT and MAP), and there is a linear relationship between soil aggregate Δδ13C (calculated by subtracting PF from NF) and MAT and MAP. The soil aggregate C and N concentrations, and δ13C and δ15N show clear trends along the climatic transect. In addition, the impacts of LCC are more obvious in topsoil than in subsoil. Our findings highlight that the impacts of LCC on soil C and N concentrations are related to climatic factors. Specifically, that the increased decomposition of soil C in PF than NF can be compensated by higher C inputs with increasing MAT and MAP.