Optimizing nitrogen management can improve stem lodging resistance and stabilize grain yield of japonica rice in rice-crayfish coculture systems

Nitrogen (N) is a major factor affecting rice yield and lodging resistance. Previous studies have primarily investigated the impact of N management on rice lodging in conventional rice monoculture (RM); however, few studies have performed such investigations in rice-crayfish coculture (RC). We hypothesized that RC would increase rice lodging risk and that optimizing N application practices would improve rice lodging resistance without affecting food security. We conducted a two-factor (rice farming mode and N management practice) field experiment from 2021 to 2022 to test our hypothesis. The rice farming modes included RM and RC, and the N management practices included no nitrogen fertilizer, conventional N application, and optimized N treatment. The rice yield and lodging resistance characteristics, such as the morphology, mechanical and chemical characteristics, anatomic structure, and gene expression levels, were analysed and compared among the different treatments. Under the same N application practice, RC decreased the rice yield by 11.1–24.4% and increased the lodging index by 19.6–45.6% compared with the values yielded in RM. In RC, optimized N application decreased the plant height, panicle neck node height, centre of gravity height, bending stress, and lodging index by 4.0–4.8%, 5.2–7.8%, 0.5–4.5%, 5.5–10.5%, and 1.8–19.5% compared with those in the conventional N application practice, respectively. Furthermore, it increased the culm diameter, culm wall thickness, breaking strength, and non-structural and structural carbohydrate content by 0.8–4.9%, 2.2–53.1%, 13.5–19.2%, 2.2–24.7%, and 31.3–87.2%, respectively. Optimized N application increased sclerenchymal and parenchymal tissue areas of the vascular bundle at the culm wall of the base second internode. Furthermore, optimized N application upregulated genes involved in lignin and cellulose synthesis, thereby promoting lower internodes on the rice stem and enhancing lodging resistance. Optimized N application in RC significantly reduced the lodging index by 1.8–19.5% and stabilized the rice yield (>8,570 kg ha^–1 on average). This study systematically analysed and compared the differences in lodging characteristics between RM and RC, and these findings will aid in the development of more efficient practices for RC that will reduce N fertilizer application.