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.

中文翻译：

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描述钙在土壤中金属结合的有机碳的大规模分布中的作用

金属结合的有机碳（OC）对于土壤有机碳（SOC）的持久性至关重要。但是，其在不同土地类型（例如高地与湿地）中的相对重要性仍不清楚。在这里，通过对比传统环境中62种土壤的经典柠檬酸盐-碳酸氢盐-二硫代石方法（OC _CBD）分析了金属结合的OC ，我们发现OC _CBD在湿地中的SOC（OC _CBD％）与旱地一样重要。土地用途类型和钙（Ca）含量是OC _CBD％的最佳预测指标，这可能是由于OC与硫酸盐可萃取的Ca（OC _Na2SO4）直接相关，以及Ca对OC _CBD的桥接和聚集作用所致。通过进一步分离OC_Na2SO4，我们发现OC- _Na2SO4约占藏蒙草原草原OC _CBD的24％，其对OC _CBD的相对贡献沿pH梯度呈S形变化（6-9）。这些发现凸显了Ca对区域范围内金属结合的OC分布的重要影响。