Potassium fertilizer management improves rice yield by optimizing the morphological and physiological characteristics of leaves under shading stress

Shading stress reduces rice yield by decreasing leaf photosynthesis. Potassium fertilization increases LAI and leaf photosynthesis of rice. Potassium panicle fertilization mitigates the adverse effect of shading on rice yield. 1 Potassium (K) improves the grain yield and stress resistance of crops; however, its effect on rice under shading stress is unclear. In this study, a two-factor split-plot experiment was conducted in Sichuan, China, to evaluate the influence of K management methods on the morphological and physiological characteristics of leaves and grain yield under shading stress. The results showed that leaf morphological and physiological traits had a greater relationship with grain yield under shading stress than under full sunlight. Compared to full sunlight control, shading stress significantly increased the leaf area index (LAI) by improving the green leaf number and leaf area of rice. Shading stress also significantly increased the chlorophyll, K + , and Na + contents, but decreased the specific leaf weight, ratios of grain-to-leaf area and chlorophyll a / b , net photosynthetic rate ( P n ), and sucrose and starch contents. This resulted in a 16.21–29.71% reduction in grain yield by reducing the seed setting rate and 1,000-grain weight. Compared to the no potassium application control (K 0-0 ), the green leaf number and leaf area of rice were significantly increased by K fertilizer, resulting in 15.61–29.88% and 13.46–22.20% increases in the total LAI under full sunlight control and shading stress, respectively. K fertilizer significantly improved the chlorophyll b , K + , and K + /Na + contents, but decreased the chlorophyll a / b ratio under shading stress, thereby enhancing P n and increasing the sucrose and starch contents of flag leaves. Therefore, K fertilizer significantly increased the grain yield by 5.57–17.35% under shading stress. Compared to 90 kg ha -1 of K 2 O single use as basal fertilizer (K 90-0 ), 90 kg ha -1 of K 2 O single use as panicle fertilizer at panicle initiation stage (K 0-90 ) significantly increased the P n and starch content of flag leaves under shading stress. Furthermore, there was no significant difference between the grain yields of K 0-90 and 180 kg ha -1 of K 2 O equal-spilt applicated as basal and panicle fertilizers (K 90-90 ) in 2021 (except under shading stress) and 2022. Overall, K fertilizer, particularly panicle K, improved the LAI and photosynthetic performance of rice, resulting in an improved rice grain yield under shading stress.