Effects of irrigation and silicon application on leaf microstructure, photosynthetic characteristics and yield of winter wheat

Irrigation is an important cultivation measure that affects plant growth and photosynthesis, and silicon fertilizers can effectively improve the photosynthetic characteristics of crops under low-water conditions. Although many studies exist on the effects of different irrigation systems and silicon application treatments on the growth and yield of winter wheat, only a few have highlighted the effects of silicon application on the microstructure and photosynthetic rate of winter wheat leaves under different irrigation systems. To explore the effects of different irrigation and silicon treatments on the development of photosynthetic organs and yield components of winter wheat, a two-factor experiment was conducted with three groups of irrigation treatments W₀: no irrigation in spring; W₁: irrigation once in spring (irrigation at jointing stage); W₂: irrigation twice in spring (irrigation once at jointing stage and flowering stage respectively) and two groups of silicon fertilizer treatments foliar sprayed with fresh water (Si₀) and foliar sprayed with silicon fertilizer (Si₁) from 2021 to 2023. Six treatments were used to analyze the effects of spraying silicon fertilizer on leaf microstructure, photosynthetic characteristics, and yield composition of winter wheat under different irrigation systems. The results showed that, with increasing irrigation time, the mesophyll cell size, leaf thickness, relative chlorophyll content, and net photosynthetic rate of winter wheat increased. Compared with W₀ treatment, the spike number per unit area, grain number per spike, 1000-grain weight, and grain yield of W₁ treatment increased by 11.4%, 6.8%, 1.5%, and 16.4%, respectively, and those of W₂ treatment increased by 15.5%, 12.4%, 4.8%, and 37.4%, respectively. The application of silicon fertilizer increased the leaf thickness of winter wheat, delayed the degradation of chlorophyll in flag leaves, and increased the net photosynthetic rate, which contributed to the increase in the number of spikes per unit area by 4.9% and grain yield by 3.3%; the promotional effect of silicon application on the yield of winter wheat diminished with the increase of irrigation frequency. Compared with Si₀, the spike number per unit area and grain yield of winter wheat increased by 8.8% and 8.3%, respectively, under W₀ treatment and increased by 4.2% and 3.4%, respectively, under W₁ treatment. Correlation analysis showed that winter wheat grain yield was positively correlated with mesophyll cell size, leaf thickness, relative chlorophyll content, and net photosynthetic rate. In summary, under the conditions of this study, increasing irrigation was beneficial in increasing the relative chlorophyll content and net photosynthetic rate of winter wheat, reducing the decrease in relative chlorophyll content and net photosynthetic rate in the middle and late grain-filling stages, and promoting an increase in spike number per unit area, grain amount per spike, 1000-grain weight, and grain yield. Spraying foliar silicon fertilizer improved the leaf structure of winter wheat in the experimental area, enhanced photosynthetic capacity, and increased the spike number per unit area and grain yield of winter wheat. The effect of spraying foliar silicon fertilizer on increasing yield was more obvious when water was insufficient.