Mapping Soil Carbon from Cradle to Grave: ‘Omic and Isotope Based Measurements of Root C Transformations

Carbon cycling in the rhizosphere is a nexus of biophysical interactions between plant roots, microorganisms, and the soil organo-mineral matrix. Plant roots are the primary inputs of soil organic C; the presence of roots significantly alters rates of organic matter mineralization by soil microbes. Our research on how roots influence decomposition of soil organic matter in both simplified and complex microcosms uses geochemical characterization, molecular microbiology, isotope tracing, ‘omics and novel imaging approaches (‘ChipSIP’ and ‘STXM-SIMS’) to trace the fate of isotopically labelled root exudates and plant tissues. Our work seeks to understand the genomic basis for how organic C transformation and decomposition in soil is altered by interactions between plant roots and the soil microbial community (bacteria, archaea, fungi, microfauna). We hypothesize that root-exudate stimulation of soil microbial populations results in the altered expression of transcripts and proteins involved in decomposition of macromolecular C compounds. Using an isotope array that allows us to follow root C into bacterial, fungal, and microfaunal communities, we have tracked movement of ¹³C from labeled exudates and ¹⁵N from labeled root litter into the soil microbial community, and linked this data to 16S profiles and community gene transcripts. By integrating stable isotopes as tracers of natural resource utilization (i.e. root litter), and analysis of the functional properties of the communities that respond to those resources, we can identify the molecular pathways that are stimulated in the soil microbiome in response to root litter, living roots, and their interfaces.