Nitrogen regulated reactive oxygen species metabolism of leaf and grain under elevated temperature during the grain-filling stage to stabilize rice substance accumulation

Rational additional nitrogen is an important agronomic measure to cope with the adverse effects of warming on rice production. However, the mechanism by which nitrogen mitigated the adverse impact of substance accumulation due to elevated temperature is poorly clarified. Therefore, in this study, a field warming experiment during grain filling and 60 kg·ha⁻¹ of additional nitrogen was established. Under elevated temperature, panicle temperature was higher and increased more substantially than leaf temperature. However, nitrogen application did not significantly reduce the leaf, panicle, and canopy temperatures. Additional nitrogen under elevated temperature delayed the decline of chlorophyll, maintained leaf photosynthesis, and prolonged grain-filling period to alleviate the decrease of starch due to warming. Hydrogen peroxide (H₂O₂) was sensitive to elevated temperature in leaves and grains. However, application of nitrogen under elevated temperature improved the activity of antioxidant enzymes to mitigate the increase of H₂O₂, resulting in a 30.31 % and 45.33 % decrease of H₂O₂ in leaves and grains compared to elevated temperature, respectively. Elevated temperature promoted the expression of heat-responsive genes, especially HSP16.9 and HSP26.7, which were consistently increased in response to warming at 5–30d after flowering. In addition, the expression of HSP16.9 at 5d and 10d after flowering and HSP26.7 at 10d after flowering was further increased with nitrogen application under elevated temperature. Therefore, HSP may be the key regulator of grain response to warming with additional nitrogen under elevated temperature. In conclusion, the relevant results revealed the physiological mechanism of nitrogen to guarantee substance accumulation and provided new ideas for cultivation measures to protect against the likely scenario of global warming.