Synergistic Effects of Nitrogen and Potassium on Quantitative Limitations to Photosynthesis in Rice (Oryza sativa L.)

The inhibition of the net CO2 assimilation (A) during photosynthesis is one of the major physiological effects of both nitrogen (N) and potassium (K) deficiencies on rice growth. Whether the reduction in A arises from a limitation in either the diffusion and biochemical fixation of CO2 or photochemical energy conversion is still debated in relation to N and K deficiencies. In this study, the gas exchange parameters of rice under different N and K levels were evaluated and limitations within the photosynthetic carbon capture process were quantified. A was increased by 17.3 and 12.1% for the supply of N and K, respectively. The suitable N/K ratio should be maintained from 1.42 to 1.50. The limitation results indicated that A is primarily limited by the biochemical process. The stomatal conductance (LS), mesophyll conductance (LM), and biochemical (LB) limitations were regulated by 26.6–79.9, 24.4–54.1, and 44.1–75.2%, respectively, with the N and K supply.