Impact of Arabidopsis thaliana Root Exudates on Dissimilatory Nitrate Reduction to Ammonium (DNRA) Activities in Shewanella loihica PV-4 and Agricultural Soil Enrichments

Enhancement of dissimilatory nitrate/nitrite reduction to ammonium (DNRA) in agricultural soils has recently gained attention as a means to decelerate nitrogen loss. Here, the potential effects of plant root exudates on the DNRA activity of a model organism Shewanella loihica and agricultural soil consortia were examined. The chemical composition of the root exudate collected from Arabidopsis thaliana (Col-0) plant was analyzed by gas chromatography time-of-flight mass spectrometry (GC TOF-MS) and applied to S. loihica cultures grown on lactate and $${\text{NO}}_{3}^{{^{ - } }}$$ to examine the effects on the $${\text{NO}}_{3}^{{^{ - } }}$$ fate. Additionally, artificial root exudate was synthesized consisting of the major root exudate constituents, and its impacts on denitrification vs. DNRA competition in agricultural soil extracts, as well as S. loihica cultures, were investigated. Incubation of S. loihica in media amended with A. thaliana root exudates or artificial root exudates both resulted in a significant enhancement of DNRA activity. The agricultural soil consortia amended with root exudates did not exhibit significant DNRA enhancement; however, artificial root exudates addition had significant DNRA enhancement effect, which was confirmed with $$^{{{15}}} {\text{NH}}_{4}^{ + }$$ production from added $$^{{{15}}} {\text{NO}}_{3}^{{^{ - } }}$$ . The findings of this study suggest that plants’ root exudates may have stimulatory impact on the environmentally beneficial DNRA pathway.