Enhanced Mineral Preservation Rather Than Microbial Residue Production Dictates the Accrual of Mineral-Associated Organic Carbon Along a Weathering Gradient

Mineral preservation and microbial residue production are vital for the accumulation of mineral-associated organic carbon (MAOC) in soils. However, their relative importance and interactive effects remain unclear. Here MAOC content and composition are analyzed in tandem with soil mineral and microbial attributes along a weathering gradient on a volcanic soil sequence. We find that MAOC content increases with increasing mineral weathering states, accompanied by increasing microbial contribution to MAOC. Mineral attributes rather than microbial physiological traits are strongly related to MAOC contents, suggesting that weathering-enhanced mineral preservation capacity overrides microbial residue production in governing MAOC accumulation by increasing reactive minerals. Furthermore, mineral attributes have a strong interactive effect with microbial traits on MAOC accumulation and composition, likely related to increasing fungal abundance in the microbial community with increasing weathering. These findings highlight that mineral weathering may effectively boost persistent SOC in synergy with microbial conversion in the long term. The accrual of mineral-associated organic carbon (MAOC) is one of the key mechanisms promoting the long-term sequestration of atmospheric CO2 into soil organic carbon (SOC). Both microbial residue production and mineral preservation are vital for MAOC accumulation. However, their relative importance and interactive effects remain unclear, hampering our ability to understand how to effectively increase this important pool of persistent SOC. Here by analyzing MAOC content and composition in tandem with soil mineral and microbial attributes along a weathering gradient on a volcanic soil sequence (290 years-2.1 million years ago), we find that MAOC content increases with increasing weathering states, accompanied by increasing microbial contribution to MAOC. In contrast to short-term studies where microbial residue production predominantly influences MAOC accumulation, weathering-enhanced mineral preservation capacity overrides microbial residue production in governing MAOC accumulation in the long term by increasing reactive minerals. Furthermore, mineral attributes have a strong interactive effect with microbial traits on MAOC accumulation and composition, likely by enhancing the accumulation efficiency of microbial residues via affecting the microbial community composition. Our findings highlight mineral weathering may effectively boost persistent SOC pools in synergy with microbial conversion. The relative importance of mineral versus microbial attributes and their interactive effects in MAOC accumulation was compared Weathering-enhanced mineral preservation overrode microbial residue production in governing MAOC accumulation over the weathering gradient Mineral weathering strengthened microbial contribution to MAOC via affecting microbial community composition