Differential responses of mineral-associated organic carbon and particulate organic carbon upon desertification of the Inner Mongolian grassland.

Introduction: Grassland desertification substantially reduces soil organic carbon (SOC) stocks. However, the responses of two distinct SOC fractions-mineral-associated organic carbon (MAOC) and particulate organic carbon (POC)-to desertification, as well as the underlying mechanisms governing these responses, remain poorly understood. Methods: To address this knowledge gap, we conducted a field study across the typical steppe (TS) and desert steppe (DS) ecosystems of Inner Mongolia, China, to investigate the dynamics of MAOC and POC and their underlying drivers, including iron/aluminum (Fe/Al) oxides, exchangeable calcium (Ca Results: Our results reveal a significant decline in MAOC concentrations under desertification, with mean values of 15.66 g/kg (0-10 cm) and 14.99 g/kg (10-20 cm) in the TS, and 12.10 g/kg (0-10 cm) and 11.64 g/kg (10-20 cm) in the DS. Unlike MAOC, POC concentrations significantly varied in only the surface layers of TS and DS, with mean values of 6.22 g/kg in the TS and 4.73 g/kg in the DS. This indicates divergent vertical responses of MAOC and POC to grassland desertification. In the DS, reduced fungal abundance-coupled with lower concentrations of amorphous Fe/Al oxides (Fe Discussion: This study provides the first comprehensive assessment of the differential responses of MAOC and POC to desertification in Inner Mongolian grasslands and elucidates the associated biogeochemical mechanisms.