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

The inhibition of the net CO 2 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 CO 2 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 ( L S ), mesophyll conductance ( L M ), and biochemical ( L B ) limitations were regulated by 26.6–79.9, 24.4–54.1, and 44.1–75.2%, respectively, with the N and K supply.