Biotic and Abiotic Factors Controlling Spatial Variation of Mean Carbon Turnover Time in Forest Soil

Soil carbon persistence in forests plays a pivotal role in regulating terrestrial feedback to climate change. However, the relative contributions of biotic and abiotic factors in controlling geographic variation of forest soil carbon turnover time (tau(soc)) remains unclear. Here, we first sampled soils from 12 permanent forest plots across eastern China and detected higher radiocarbon-derived mean turnover time of soil organic carbon in the deep (30-100 cm; 2,087 +/- 246 years) than the surface (0-30 cm; 249 +/- 80 years) layer. Further analyses based on the partial Mantel test and structural equation model illustrated that the interactions of climate, vegetation, and soil factors are more complex in deep than surface soils. Then, we established a global database of radiocarbon-derived tau(soc) from 1897 forest soil samples. On the global scale, tau(soc) was significantly higher in the deep (3,081 +/- 398 years) than the surface (332 +/- 56 years) layer. Soil depth alone explained 11.7% of the spatial variation in tau(soc), and the interactions between climate, stand age, and soil depth account for 68.6% of the variation. These findings highlight the joint control of climate, vegetation, and soil depth in the spatial variation of soil carbon persistence in global forests. Plain Language Summary The soil in the forest ecosystem plays a vital role in modulating feedback between the atmosphere and biosphere under climate change. However, the underlying mechanism of climatic, vegetation, and soil properties regulating soil carbon turnover time (tau(soc)) at a geographic scale is still unclear. Here, we established a local data set by collecting soil samples from 12 permanent forest plots in eastern China. The statistical results showed significantly longer tau(soc) in the deep layer than in the surface layers and different processes at two depths. We then established a global database of forest stand age and radiocarbon-derived tau(soc). This study provides fundamental evidence of joint control of climate, vegetation, and soil factors in the spatial variation of soil carbon persistence in global forests.