Soils store more carbon than the atmosphere and biosphere combined, yet the mechanisms that regulate soil C remain elusive. While plant roots are the dominant source of carbon (C) that enters belowground food webs, microbial transformations of this C determine whether it is retained as soil organic matter (SOM) or returned to the atmosphere (CO2, CH4). Since soil C and associated organic molecules are so critical to soil fertility, water holding capacity, and the C balance of our planet, a predictive understanding of soil C residence time and turnover (i.e. ‘persistence’) is essential. It has recently become clear that microbial cell materials (‘necromass’) play a critical role in the persistence of SOM. However, current soil C models continue to emphasize stabilization by abiotic mechanisms (sorption, occlusion, and recalcitrance), largely ignoring the impacts of microbial ecophysiology. We hypothesize that microbial biochemistry, functional potential and physiology may be of comparable, or greater importance relative to abiotic stabilizing effects. We further suggest that the basis of microbial impacts results from their specific ecophysiological ‘traits’ (e.g. cell wall composition, hyphal growth, EPS production, spore formation, carbon use efficiency, extracellular enzymes, adhesion genes, and specific growth rate) that can be genomically resolved through soil metagenomics and quantified via isotope tracing.
Results/Conclusions
In this presentation, I will discuss a list of potential traits that may be fruitful targets for metagenomic studies evaluating the persistence and importance of microbial products as SOM precursors. With new quantitative stable isotope probing approaches, it is now possible to link these genome-resolved ecophysiology traits to directly measure taxon-specific population dynamics. I will also discuss our results showing that soil mineral type influences the microbial communities that colonize mineral surfaces. With rhizosphere isotope tracing, we find that plant carbon that flows to soil microbial cells is transformed in the process, and that both microbially-transformed carbon and microbial cell materials directly associate with mineral surfaces. Finally, I will propose a series of integrated approaches that used together can examine how genomic capacity and activities of soil microbiomes are shaped by edaphic conditions (moisture, temperature, redox regimes) and fundamentally affect the terrestrial soil C pool.