Role of Fe and Mn in organo-mineral-microbe interactions: evidence of carbon stabilization and transformation of organic matter leading to carbon greenhouse gas emissions.

Up to 90% of organic matter (OM) in soils and sediments are stabilized and protected against microbial decomposition through organo-mineral interactions, formation of soil aggregates, pH and oxygen availability. In soils and sediment systems OM is associated with mineral constituents promoting carbon persistence and sequestration of which iron (Fe) and manganese (Mn) are crucial components. Under anoxic condition, microbes couple the decomposition of OM to the oxidative/reductive transformation of Fe/Mn minerals leading to carbon greenhouse gas (C-GHG) emissions (i.e., CH4 and CO2). Although these organo-mineral-microbe interactions have been observed for decades, the bio-geochemical mechanisms governing the switch from OM stability toward OM degradation are not fully understood. Interest in this field have been growing steadily given the interest in global warming caused by OM decomposition leading to C-GHG emissions. This review emphasizes the dual role of Fe/Mn minerals in both OM stability and decomposition. Additionally, we synthesize the conceptual understanding of how Fe/Mn minerals govern OM dynamics and the resultant C-GHG emissions via microbial-mediated carbon transformation. We highlight the need for interdisciplinary research to better understand organo-Fe/Mn mineral-microbial interactions to develop management handles for climate mitigation strategies.