PNNL

Abstract

Plant roots and associated microbes release a diverse range of functionally distinct exudates into the surrounding rhizosphere, with direct impacts on soil carbon storage, nutrient availability, and contaminant dynamics. Yet mechanistic linkages between root exudation and emergent biogeochemical processes remain poorly resolved, largely due to difficulties associated with probing dynamic rhizosphere environments. Here we show that spatiotemporal dynamics of exudates during root growth coincide with the emergence of distinct biogeochemical microenvironments. Using a novel combination of in-situ microsensors with high-resolution mass spectrometry, we found significant variations in metabolites and dissolved organic carbon (DOC) as well as microbial growth, redox, and pH dynamics during root growth and maturation. Surprisingly, the amount of DOC did not significantly correlate with variations in other biogeochemical parameters. However, the presence of specific sugars significantly correlated with declines in redox potential, while that of specific phenols and organic acids significantly correlated with declines in pH following the arrival of the root tip. Our results suggest the differential release of functionally diverse exudates along growing plant roots creates biogeochemically distinct microenvironments within the rhizosphere. This work suggests that the fate of carbon, nutrients and contaminants in soils are, in part, regulated by transient microenvironments in the rhizosphere.