Delineating the Role of Calcium in the Large‐Scale Distribution of Metal‐Bound Organic Carbon in Soils
Simin Wang, Yufu Jia, Ting Liu, Yiyun Wang, Zongguang Liu, Xiaojuan Feng
Abstract
Abstract Metal‐bound organic carbon (OC) is vital for the persistence of soil organic carbon (SOC). However, its relative importance in different land types (e.g., upland vs. wetland) remains unclear. Here by analyzing metal‐bound OC by the classic citrate‐bicarbonate‐dithionite method (OC CBD ) from 62 soils from contrasting environments, we find that OC CBD constitutes an equally important proportion of SOC (OC CBD %) in wetlands as in uplands. Land‐use type and calcium (Ca) content are the best predictors of OC CBD %, likely owing to the contribution of OC directly associated with sulfate‐extractable Ca (OC Na2SO4 ) and Ca's bridging and aggregating effect on OC CBD . By further separating OC Na2SO4 , we find that OC Na2SO4 accounts for ∼24% of OC CBD in Tibetan‐Mongolian grasslands and its relative contribution to OC CBD shift in an S‐shaped mode along the pH gradient (6–9). These findings highlight Ca's important effect on the distribution of metal‐bound OC at regional scales.