Enhancing rice nitrogen use efficiency via plant-microbe-soil interactions: Insights from 15N tracing

Abstract

To improve crop fertilizer nitrogen use efficiency (NUE) for sustainable agriculture, it is important to understand plant-microbe-soil interactions. Here we use a ¹⁵N tracing technique to characterize the gross N transformation rates in rice-soil systems. We found that rice cultivation inhibited gross N mineralization (M) by 70 %, compared with the bulk soil. Gross NH₄⁺ oxidation (O_NH4) and gross NH₄⁺ immobilization (I_NH4) in the rhizosphere were also significantly reduced. In contrast, gross heterotrophic nitrification (O_Nrec) significantly increased. Slow release of organic N and low NH₄⁺ oxidation were beneficial for improving rice N absorption efficiency, reducing N loss in flooded paddy field. Rice NUE is mainly controlled by NH₄⁺ uptake, while soil pH plays a central role in regulating the rice NH₄⁺ uptake rate. The stimulation of O_NH4 and I_NH4 due to rising pH had a negative impact on rice NH₄⁺ uptake. NUE also differed with respect to the rice varieties. Rice NH₄⁺ uptake accelerated with increasing M but was negatively correlated with I_NH4 and O_NH4. Nitrate uptake, on the other hand, was positively correlated with O_Nrec but negatively correlated with I_NH4. Our analysis revealed that rice cultivars with high N uptake capacity can regulate the soil N transformation rates and microbial properties in the rhizosphere to meet their N demand. The negative correlation between rice NH₄⁺ uptake and bacterial abundance also suggests that microbial competitiveness was declining. These results contribute to our understanding of agroecosystem with low N input by optimizing microbially-mediated soil N transformations.