Effects of silicon application on diurnal variations of physiological properties of rice leaves of plants at the heading stage under elevated UV-B radiation

We investigated the effects of silicon (Si) application on diurnal variations of photosynthetic and transpiration physiological parameters in potted rice (Oryza sativa L. cv Nanjing 45) at the heading stage. The plants were subjected to two UV-B radiation levels, i.e., reference UV-B (A, ambient, 12.0 kJ m⁻² day⁻¹) and elevated UV-B radiation (E, a 20 % higher dose of UV-B than the reference, 14.4 kJ m⁻² day⁻¹), and four Si application levels, i.e., Si₀ (no silicon supplementation, 0 kg SiO₂ ha⁻¹), Si₁ (sodium silicate, 100 kg SiO₂ ha⁻¹), Si₂ (sodium silicate, 200 kg SiO₂ ha⁻¹), and Si₃ (slag silicon fertilizer, 200 kg SiO₂ ha⁻¹). Compared with the reference, elevated UV-B radiation decreased the diurnal mean values of the net photosynthetic rate (Pn), intercellular carbon dioxide (CO₂) concentration (Ci), transpiration rate (Tr), stomatal conductivity (Gs), and water use efficiency (WUE) by 11.3, 5.5, 10.4, 20.3, and 6.3 %, respectively, in plants not supplemented with silicon (Si₀), and decreased the above parameters by 3.8–5.5, 0.7–4.8, 4.0–8.7, 7.4–20.2, and 0.7–5.9 %, respectively, in plants treated with silicon (Si₁, Si₂, and Si₃), indicating that silicon application mitigates the negative effects of elevated UV-B radiation. Under elevated UV-B radiation, silicon application (Si₁, Si₂, and Si₃) increased the diurnal mean values of Pn, Ci, Gs, and WUE by 16.9–28.0, 3.5–14.3, 16.8–38.7, and 29.0–51.2 %, respectively, but decreased Tr by 1.9–10.8 %, compared with plants not treated with silicon (E+Si₀), indicating that silicon application mitigates the negative effects of elevated UV-B radiation by significantly increasing the P ₙ, C ᵢ, G ₛ, and WUE and decreasing the T ᵣ of rice. Evident differences existed in mitigating the depressive effects of elevated UV-B radiation on diurnal variations of physiological parameters among different silicon application treatments, exhibiting as Si₃>Si₂>Si₁>Si₀. In addition to recycling steel industrial wastes, the application of slag silicon fertilizer mitigates the negative effects of elevated UV-B radiation on photosynthesis and transpiration in rice.