Endophytes Enhance Rice Inorganic Nitrogen Use Efficiency and Mitigate Nitrogen Loss Via Dissimilatory Nitrate Reduction To Ammonium in Paddy Soils

Rice cultivation involves the large amounts of fertilizers application, but nitrogen (N) use efficiency remains low. Endophytes are considered key microorganisms that regulate nitrogen utilization and gaseous nitrogen loss in rice paddy ecosystems. However, systematic studies on the effectiveness and underlying mechanisms of endophytes in nitrogen utilization by crops within paddy fields are still scarce. This study employed microcosmic experiments to investigate the effects of endophytes on gaseous nitrogen loss from paddy soil and inorganic nitrogen utilization in rice plants. Results demonstrated that colonization of endophytes increased the efficiency of inorganic N use by approximately twofold. The simultaneous addition of rice roots colonized with endophytes to the soil resulted in a significant increase in ammonium (NH₄⁺) concentrations by 121-138% as well. Notably, colonization with endophytes reduced cumulative nitrous oxide (N₂O) emissions by 13-21% compared to the control. Importantly, the endophytes were shown to enhance soil redox capacity by increasing Clostridium abundance and Fe²⁺ concentration, thereby promoting the dissimilatory nitrate reduction to ammonium (DNRA) and mitigating soil N loss. These findings underline the potential of rice endophytes in paddy field management to enhance soil nitrogen retention and reduce nitrogen loss.