Combined action of salicylic acid and silicon regulates osmoregulatory substances and antioxidant enzymes to improve drought tolerance and yield in dry-cultivated rice

Salicylic acid (SA) and silicon (Si) protect against a variety of stresses. Our group found that Si improved the drought tolerance of dry-cultivated rice. No studies are available regarding the synergistic effect of aboveground SA spraying and belowground Si application on the drought tolerance and yield of dry-cultivated rice, necessitating further research. Two rice types with different levels of drought resistance (Suijing18 and Hongke88) were selected for this study. The optimal SA concentration (1 mM/L) was determined via five different SA spraying treatments at various concentrations. Then SA and Si were combined, which included a Control, 45 kg/hm ² Si, 1 mM SA, and 1 mM SA + 45 kg/hm ² Si to examine their synergistic effect on the morphological characteristics, yield, osmotic regulatory substances, chlorophyll fluorescence, and antioxidant enzymes of two different drought-resistant rice cultivars. The results showed that combined SA + Si application increased the plant height, root length, aboveground dry weight, and belowground dry weight of these two drought-resistant rice types. The yield of which increased by 80.70% and 77.26%, respectively. Compared with the control, while the photosynthetic capacity improved significantly, the minimum photochemical efficiency (Fv/Fm) values increased by 30.97% and 19.17%, while the photochemical quantum yield (ΦPSII) values were 29.01% and 29.64% higher, the NPQ values decreased by 67.55% and 39.98%, respectively. Moreover, treatment increased the soluble sugar and soluble protein levels, osmoregulatory capacity, antioxidant enzyme activity, and increased endogenous SA + Si content in the two dry-cultivated rice species. Hence, the combined application of SA and Si improves the drought resistance of dry-cultivated rice by increasing the content of osmoregulatory substances, enhancing the levels of endogenous SA and Si, upregulating the activity of antioxidant enzymes, and strengthening the photosynthetic capacity of the PSII system. This results in improved drought-resistant capability and increase of the accumulation of dry matter and yield of dry-cultivated rice, which produces a more significant alleviation of the adverse effects of drought stress compared to the application of either substance alone.