Effects of land use change from natural forest to plantation on C, N and natural abundance of (13)C and (15)N along a climate gradient in eastern China

Soil C and N turnover rates and contents are strongly influenced by climates (e.g., mean annual temperature MAT, and mean annual precipitation MAP) as well as human activities. However, the effects of converting natural forests to intensively human-managed plantations on soil carbon (C), nitrogen (N) dynamics across various climatic zones are not well known. In this study, we evaluated C, N pool and natural abundances of δ(13)C and δ(15)N in forest floor layer and 1-meter depth mineral soils under natural forests (NF) and plantation forest (PF) at six sites in eastern China. Our results showed that forest floor had higher C contents and lower N contents in PF compared to NF, resulting in high forest floor C/N ratios and a decrease in the quality of organic materials in forest floor under plantations. In general, soil C, N contents and their isotope changed significantly in the forest floor and mineral soil after land use change (LUC). Soil δ(13)C was significantly enriched in forest floor after LUC while both δ(13)C and δ(15)N values were enriched in mineral soils. Linear and non-linear regressions were observed for MAP and MAT in soil C/N ratios and soil δ(13)C, in their changes with NF conversion to PF while soil δ(15)N values were positively correlated with MAT. Our findings implied that LUC alters soil C turnover and contents and MAP drive soil δ(13)C dynamic.