Speciation of Ca-bearing minerals and its relation to MAOM in semi-arid agricultural soils: a combined XRPD - XANES approach

Calcium (Ca) is increasingly recognized as a key factor in promoting carbon persistence in semi-arid soils, which are typically characterized by low soil organic carbon content, alkaline pH, and Ca abundance. However, direct evidence or a clear mechanistic understanding of Ca contribution to carbon persistence remains limited, due partly to the lack of established techniques for determining Ca species in soils, especially Ca-bearing minerals. We therefore aimed to investigate the relationship between Ca species and mineral-associated organic matter (MAOM) fraction (>1.7 g cm-3,