SOM and Microbes—What Is Left From Microbial Life

Understanding processes of soil organic matter (SOM) formation is crucial for sustainable land use and for mitigation of global change. In recent decades, novel analytical tools have allowed significant progress in this field. SOM is now considered to be a continuum of plant and microbial residues at various stages of decay. Microbial residues play a particularly important role in SOM formation, which is embedded in the trilateral interrelationship between soil, plants, and microorganisms. Plant-derived material is processed by microorganisms into microbial biomass and finally necromass. Microbial carbon-use efficiency and stabilized necromass are thus the key flux-controlling factors. Carbon use efficiency depends on microbial metabolism and on environmental factors. Further degradation of microbial necromass is prevented by its spatial organization and by interactions with soil minerals. Here we provide the latest insights into these processes, with the aim of providing considerable help in developing and improving process-based models of SOM turnover and sustainable soil management.