Abstract
Combined application of nitrogen (N) and potassium (K) fertilizer could significantly enhance crop yield. Crop yield and photosynthesis are inseparable. However, the influence of N and K interaction on photosynthesis is still not fully understood. Field and hydroponic experiments were conducted to examine the effects of N and K interaction on leaf photosynthesis characteristics and to explore the mechanisms in the hydroponic experiment. CO2 conductance and carboxylation characteristic parameters of oilseed leaves were measured under different N and K supplies. Results indicated that detectable increases in leaf area, biomass and net photosynthetic rate (An) were observed under optimal N and K supply in field and hydroponic experiments. The ratio of total CO2 diffusion conductance to the maximum carboxylation rate (gtot/Vcmax) and An presented a linear‐plateau relationship. Under insufficient N, increased K contributed to the CO2 transmission capacity and improved the proportion of N used for carboxylation, promoting gtot/Vcmax. However, the low Vcmax associated with N insufficiency limited the An. High N supply obviously accelerated Vcmax, yet K deficiency led to a reduction of gtot, which restricted Vcmax. Synchronous increases in N and K supplementation ensured the appropriate ratio of N to K content in leaves, which simultaneously facilitated gtot and Vcmax and preserved a gtot/Vcmax suitable for guaranteeing CO2 transmission and carboxylation coordination; the overall effect was increased An and leaf area. These results highlight the suitable N and K nutrients to coordinate CO2 diffusion and carboxylation, thereby enhancing photosynthetic capacity and area to obtain high crop yield.