Leaf photosynthetic capacity is regulated by the interaction of nitrogen and potassium through coordination of CO2 diffusion and carboxylation

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 (A_n ) 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 (g_tot /V_cmax ) and A_n 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 g_tot /V_cmax . However, the low V_cmax associated with N insufficiency limited the A_n . High N supply obviously accelerated V_cmax , yet K deficiency led to a reduction of g_tot , which restricted V_cmax . Synchronous increases in N and K supplementation ensured the appropriate ratio of N to K content in leaves, which simultaneously facilitated g_tot and V_cmax and preserved a g_tot /V_cmax suitable for guaranteeing CO₂ transmission and carboxylation coordination; the overall effect was increased A_n 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.