PNNL

Abstract

The rhizosphere, where plant roots interact with soil, is a hub of biogeochemical activity with ecosystem impacts on carbon stocks and soil health. While root-derived carbon has been shown to contribute more to soil carbon stocks than aboveground litter, the molecular and functional chemodiversity of root exudates remains poorly understood due to limited characterization and annotation. In this study, we investigate the potential for rhizodeposition to promote soil health and carbon persistence by quantifying carbon and nitrogen inputs and characterizing the molecular chemodiversity of metabolites and lipids in root exudates from mature tall wheatgrass (Thinopyrum ponticum) grown in a marginal soil. Rates of lipid derived carbon inputs were approximately double that of metabolites with markedly higher carbon to nitrogen ratios. Notably, in this unprecedented characterization of intact lipids in root exudates, we discovered a diversity of lipids, including substantial levels of triacylglycerols (~19 µg/g fresh root per min), fatty acyls, sphingolipids, sterol lipids, and glycerophospholipids, some of which were not previously known to be exuded by roots. This new evidence supports the significant, yet understudied role of lipids in rhizodeposition and emphasizes the importance of atmospheric CO2 transport into soil biogeochemical pathways by deep-rooted perennial plants. Our metabo-lipidomics approach substantially increased the characterization of root exudate chemodiversity by employing both tandem mass spectral library searching and deep learning-based chemical class assignment. Together our results demonstrate the significant contribution of root exudate lipids to belowground carbon inputs and unveil their chemodiversity. Our findings underscore the potential for root exudate lipids to contribute to managing or modifying root-soil carbon dynamics to promote soil health and carbon persistence.