Soil carbon quantity and form are controlled predominantly by mean annual temperature along 4000 km North-South transect of Eastern China

The forest ecosystem plays a key role in mitigating global climate change through carbon sequestration in its biomass and soils to limit the rising atmospheric concentration of CO₂. However, the combined overall interaction of climate and forest type on the quantities and forms of soil carbon (organic vs. inorganic) has not yet been sufficiently investigated. In this study, the contents of soil total carbon (STC), soil organic carbon (SOC) and soil inorganic carbon (SIC) were measured along the 4000 km North-South Transect of Eastern China. We sampled 252 soil samples (6 replicates for each site, 3 depths for each site) from four long-term ecosystem  experimental stations in Dinghushan, Shennongjia, Beijing and Changbaishan, along the transect from south to north, including 14 different forest types. The contents of STC, SOC, and SIC in the upper 60 cm soil layer varied in different types of forest with 34–107 g C kg⁻¹, 31–104 g C kg⁻¹, and 1.5–8 g C kg⁻¹, respectively. The northern fir and birch forest, most notably in Changbaishan, had the highest STC and SOC contents. The higher SIC contents were found in the southern evergreen broad-leaved forests in Dinghushan and Shennongjia. The contents of STC, SOC and SIC differed significantly in terms of mean annual temperature (MAT), mean annual  precipitation (MAP), forest type, and soil depth. In the upper 60 cm soil layer, the most significant correlations occurred between SOC (or STC) and MAT (R²_SOC = −0.62, R²_STC =−0.60) when compared with the correlation between SOC (or STC) and MAP (R²_SOC= −0.45, R²_STC=−0.45) or elevation (R²_SOC=0.48, R²_STC=0.48). The soil stratification ratio (SR) of STC and SOC were typically ~2–3 in most forests and even reached 5–7 in Changbaishan forest, indicating a well-functioning ecosystem overall. We concluded that on the near-continental scale (4000 km), forest soil carbon contents and forms (SOC, STC, SIC) were controlled most strongly by temperature (MAT). Therefore, an innovative selection of a specific forest type (fir or broad-leaved forest) within set temperature regimes can better contribute to maximizing soil carbon content and thus optimize its sequestration on the national to near-continental scale to mitigate climate change.