Dissolved Organic Carbon Changes Nitrogen Transformations by Mediating Soil‐Microbiome Interactions to Enhance Rice Nitrogen Use Efficiency

ABSTRACT Geographic variation in rice nitrogen (N) use efficiency (NUE) is shaped by complex interactions among climate, soil, and microbiome, yet the exact mechanistic drivers remain unclear. This study disentangled these effects through a factorial experiment combining microbiome reciprocal transplantation (northern vs. southern China soils) with climate condition simulations (temperate vs. subtropical conditions), using 15 N tracing and numerical modelling to quantify gross N transformation rates, plant uptake rates, and NUE. The results demonstrated that climate dominated N dynamics, with warmer southern climate conditions increasing N mineralization (+1.7 mg N kg −1 day −1 ), heterotrophic nitrification (+1.2 mg N kg −1 day −1 ), NH 4 + uptake (+5.5 mg N kg −1 day −1 ), NO 3 − uptake (+3.4 mg N kg −1 day −1 ), and NUE by 7%, while reducing soil N loss by 9%, compared to northern climates. The climatic impact on NUE was modulated by soil properties, with an 11% increase in southern soil but only 3.5% in northern soil. Soil‐microbiome interactions significantly influenced NUE ( p < 0.001), with dissolved organic carbon (DOC) identified as a key mediator that enhanced microbial biomass N, bacterial abundance and nif H gene activity to stimulate N mineralization. Notably, native soil inoculated with non‐native microbiome achieved the highest NUE (32%), revealing microbial synergy with soil properties. Structural equation modelling confirmed N mineralization as the primary driver of NUE, facilitated by DOC‐induced microbial activity. These findings reveal an innovative dual approach that integrates DOC‐driven microbiome engineering with spatially resolved soil–plant–climate simulations, demonstrating synergistic improvements in NUE and climate‐resilient ecosystem functioning.