Transect-scale controlling factors for soil microbial biomass carbon

Soil microbial biomass carbon (MBC) plays an essential role in driving and regulating global cycling of carbon (C) which is critically important to climate system. However, the pivotal transect-scale determinant factor for the content of soil MBC, along with the variation pattern in different natural forests and soils has not been sufficiently investigated. In this study, 252 soils samples (6 replicates and 3 depths for each site) were sampled from 14 forests which lie in 7 soil types along the 4000 km North-South transect of Eastern China. We found that the highest content of soil MBC in the whole soil profile with 556.69 ± 14.59 mg C kg^− 1 occurred in the subalpine coniferous forest, and the lowest content was observed with 53.11 ± 10.22 mg C kg^− 1 in warm coniferous forest. From the angle of soil type, in the whole soil profile Haplic Andosol had the highest content of soil MBC with 480 mg C kg^− 1, while Haplic ferralsol possessed the lowest content of MBC with 102 mg C kg^− 1. In addition, over the North-South transect of Eastern China the strongest correlation was observed in between the content of soil MBC and altitude (ALT) (R² = 0.64), followed by soil type (R² = -0.61), mean annual temperature (MAT) (R² = -0.56). We concluded that the content of soil MBC in natural forests is mainly controlled by ALT on a transect scale. We believed that the soil C in Yue spruce-fir forest was relatively stable, which can be an option to be a specific forest to optimize forest management and to contribute to mitigating climate change.