Silicon fertilization drives metabolite–microbe synergy to stabilize rhizosphere nitrogen supply and improve drought resilience and yield stability in upland rice

Silicon alters rhizosphere metabolites and reshapes N-cycling microbial communities. Silicon stabilizes soil nutrient cycling under drought stress. Silicon maintains antioxidant capacity, supporting drought resilience and yield stability. Metabolite–microbe interactions are pivotal hubs for maintaining crop productivity under abiotic stress, and silicon (Si) fertilization has been widely recognized for enhancing plant stress tolerance. However, the mechanisms by which Si mediates rhizosphere metabolic reprogramming and microbial regulation to synergistically improve crop drought resilience remain unclear. Here, a two-year field experiment (2023–2024) was conducted using upland rice cultivar “Hanyou 73”. Treatments included well-watered conditions (CK), drought stress (D), and four Si application rates under drought (DS1-DS4, 25, 50, 75, and 100 kg ha -1 , respectively). We systematically investigated the coupled effects of Si on rhizosphere metabolites, microbial communities, and plant stress responses. Drought stress disrupted oxidative homeostasis, reduced photosynthetic capacity, and inhibited carbon and nitrogen metabolism, resulting in yield reductions of 27.96 and 20.37% in 2023 and 2024, respectively. Compared with D, DS3 significantly increased the levels of rhizosphere N- and sugar-related metabolites and enhanced soil microbial diversity, thereby stabilizing soil nitrogen cycling and enriching beneficial taxa ( g_Bacillus ). Consequently, nitrogen use efficiency increased by 26.21%, leaf superoxide dismutase (SOD) activity increased by 40.31%, and grain yield increased by 22.98 and 20.90% across the two years. Validation experiments further demonstrated that the combined application of Si and N/sugar-related metabolites (Ethanamine, Tagatose, Urea, Sorbose, and Fumaric acid) significantly promoted upland rice growth and soil nutrient accumulation, stimulated the proliferation of strain BT021, strengthened soil N cycling, increased soil N-related enzyme activities, and enhanced plant growth and antioxidant capacity. Structural equation modeling (SEM) revealed that Si directly regulated yield variation under drought through metabolite–microbiome coupling–driven nutrient cycling. Overall, Si fertilization reshapes rhizosphere processes via metabolite–microbe synergy, improves soil N cycling and rhizosphere environmental quality under drought, promotes plant nutrient transport, and stabilizes yield, providing new mechanistic insights and an applicable paradigm for green, stress-resilient yield improvement in upland agriculture.