More microbial than plant-derived compounds preserved in the bound form: implications for microbial contribution to soil organic matter stabilization

Mineral protection is vital for soil organic matter (SOM) preservation. However, the proportions of mineral-bound organic compounds that have different structures and biological sources in soils remain unclear, impeding a deeper understanding of the mechanisms underlying OM-mineral interactions. Here we used offline pyrolysis to quantify the mineral-bound lipids in soils with increasing water content as well as aquatic sediments. The proportions of mineral-bound microbial lipids were higher than the plant-derived lipids, while the proportions of bound microbial lipids with diverse structures were at a comparable level, indicating that the importance of OM biological source may exceed the chemical structure in the formation of organo-mineral association. In addition, the proportion of bound microbial lipids was higher under drier conditions, whereas the proportion of bound plant-derived lipids was not affected by the water content. Our results indicate microbial physiology, particularly hydrotaxis, should be regarded as a new biogeochemical agent for the stability of OM.