Abstract
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 δ13C and δ15N 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 δ13C was significantly enriched in forest floor after LUC while both δ13C and δ15N values were enriched in mineral soils. Linear and non-linear regressions were observed for MAP and MAT in soil C/N ratios and soil δ13C, in their changes with NF conversion to PF while soil δ15N values were positively correlated with MAT. Our findings implied that LUC alters soil C turnover and contents and MAP drive soil δ13C dynamic.
Highlights
Soil C and N turnover rates and contents are strongly influenced by climates as well as human activities
Forest floor C mean content was lower in natural forest (NF) with 399.8 ± 86.1 g kg−1 across six sites as compared to plantation forest (PF) with 438.6 ± 70.9 g kg−1 while an opposite trend was observed in forest floor N content with 13.6 ± 1.8 g kg−1 in NF and 10.3 ± 2.6 g kg−1 in PF
Soil C ranged from 2.98 g kg−1 to 49.55 g kg−1 whereas soil N was in the range of 0.23 g kg−1 to 4.23 g kg−1 in mineral soil across the sampling sites (Table 2)
Summary
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. There are some inconsistencies in soil C and N pool estimations such as the increasing of plant cover through reforestation and afforestation programs, the lack of data from repeated inventories, the variety of methods used to assess the carbon balance of China and the variation of climate conditions within those studies which vary from one period to another. The increasing needs for timber and other economic forest products in China, means that large areas of NF has been converted to intensively managed plantations[12,34,35] but there is still significant uncertainty concerning changes in forest floor and mineral soil C and N stocks and turnover processes potentially induced by forest conversion along the 4200 km transect from northern China to southern China
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