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. The primary goal of our recently initiated JGI/EMSL project is to determine 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 tracked the movement of 13C from labeled exudates and 15N from labeled root litter into the soil microbial community. 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, our ultimate goal is to identify the molecular pathways that are stimulated in the soil microbiome in response to root litter, living roots, and their intersection.  We will use this information to identify key traits of grassland soil microorganisms that impact their fitness as members of the rhizosphere and detritosphere, and will develop and parameterize trait-based models of microbial community function to interpret and predict carbon stabilization and turnover.

Mapping soil carbon from cradle to grave: 'Omic and isotope based measurements of root C transformations

248th National Meeting (2014)

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