Microbial-accessibility-dependent electron shuttling of in situ solid-phase organic matter in soils.

Abstract The associations between electron shuttling of in situ organic matter and its microbial accessibility in natural soils remain elusive. In this study, through combining soil physical fractionation with incubation experiments, we show that the in situ solid-phase organic matter in soils is a heterogeneous pool with varied electron shuttling capacities due to the diverse soil organic matter protection mechanisms against microbial accessibility. The microbial accessibility of in situ solid-phase organic matter in soils largely acts as a crucial factor in determing the number of redox-active functional groups involved in shuttling electrons from microorganisms to Fe(III) oxides, and therefore the relationship between electron shuttling capacity of in situ solid-phase organic matter and its intrinsic chemical structures. Graphical abstract Unlabelled Image Highlights • Electron shuttling of in situ solid-phase SOM was associated with its microbial accessibility. • Not all redox-active moieties in the in situ solid-phase OM were available for shuttling electron. • In situ solid-phase SOM is a heterogeneous pool with varied electron shuttling capacities. • Electron shuttling capacity of in situ solid-phase SOM decreased with decreasing aggregate size. [ABSTRACT FROM AUTHOR]