Unlocking plant-microbial interactions in deep Mollisols in the Midwestern US: Linking depth gradients in roots, microbial activity, and soil carbon in agroecosystems

Deeply rooted perennial plants may help build soil carbon (C) stocks, but most research has focused on shallow soils, resulting in gaps in our understanding of how the balance between decomposition and C inputs shift and drive soil C accumulation with depth. To address this challenge, researchers at the Center for Advanced Bioenergy and Bioproducts Innovation (CABBI) assessed the distribution and assimilation of ¹³C-labeled simple carbon in meter-deep pits under mature perennial miscanthus stands.

Researchers dug five quantitative soil pits under mature miscanthus plots in Urbana, IL, separated and quantified fine root biomass by depth, quantified soil C, microbial respiration, and potential nitrogen mineralization and nitrification, and traced ¹³C-labeled glucose to the soils to determine the fate of simple C inputs with depth.

Fine root biomass, total soil C, mineral-associated organic C (MAOC), particulate organic C (POC), and microbial activity declined with depth. POC declined more rapidly than MAOC, resulting in an increase in MAOC:POC with depth. Incorporation of simple ¹³C inputs into MAOC were similar across depths. However, these inputs led to net MAOC losses in shallow soils and either small loses or gains in deeper soils.

This work suggests that depth gradients in soil C stocks represent a balance between inputs, decomposition, and microbial necromass production and that increase in root C inputs by deep-rooted plants may have the potential to build stable MAOC.

This work was funded by CABBI, a U.S. Department of Energy-funded Bioenergy Research Center, with a grant from the DOE Office of Science, Biological and Environmental Research Program.

Images available upon request.