THE NETWORK OF ORGANO-MINERAL-ASSOCIATION (OMA) AND DISSOLVED ORGANIC MATTER (DOM) STIMULATES ELECTRON TRANSFER OVER CM DISTANCE IN MINERAL SOILS

Electron transfer processes dominated by natural organic matter have been widely studied in organic soils, wetlands and freshwater sediments. Previous research has demonstrated that diffusion-electron hopping networks comprised of dissolved (DOM) and particulate organic matter (POM) were found to be able to mediate electron transfers over centimeter (cm) distances. However, it is still unclear whether this long-distance electron transfer also occurs in mineral soils, where POM is commonly bonded with mineral phases (i.e., organo-mineral associations, OMA) and are thus less mobile and accessible. Here we collected mineral soil samples from Schönbuch forest in Germany and extracted the DOM and OMA to investigate their roles in transferring electrons. By performing a series of microbial iron(III) reduction experiments over a 2-cm distance, we found that neither DOM nor OMA alone were able to mediate electron transfer from microbes to iron(III) minerals. Rather, the co-existence of both components significantly accelerated iron reduction. We further identified a minimum DOM to OMA ratio of 0.03 for sustaining long-distance electron transfer. Our findings demonstrate, for the first time, the ability of DOM and OMA networks in transferring electrons over centimeter distances and call for future research to focus on its effect in regulating matter and energy transformations in mineral soils.