Exploiter no more: root metabolites driving denitrification inhibition from diverse plants

Abstract

Soil denitrifiers can profoundly benefit from plant root activities by utilizing the released labile carbon (C) in root exudates, though the plants may not receive direct benefits in return. However, the role of root metabolites in promoting or suppressing denitrification remains poorly understood across a wide range of plant species. Additionally, the underlying mechanisms driving these effects are still elusive. We used an optimized hydroponic-based approach to collect root metabolites in hydroponic solution from 100 plant species. We then assessed their differential effects on soil denitrification potential, microbial activity and the abundance of denitrification genes. Out of the 100 plant species tested, the root metabolites of 21 exhibited biological denitrification inhibition (BDI), while 51 stimulated denitrification under conditions of sufficient C supply. Some of the collected BDI root solutions inhibited soil denitrifying activity within the heterotrophic community and reduced the abundance of key denitrification genes, including nirK, nirS and nosZ. Several potential BDI-related secondary metabolites, such as flavonoids, were identified using untargeted LC–MS metabolomics. Our findings suggest that the inhibition of denitrification through root metabolites may be a widespread strategy among plant species, offering new insights for developing effective strategies to mitigate plant-mediated N losses in the rhizosphere.