Ontogenetic Changes of Photosynthetic and Dark Respiration Rates in Relation to Nitrogen Content in Individual Leaves of Field Crops

Ontogenetic changes of rates of photon-saturated photosynthesis (P_sat) and dark respiration (R_D) of individual leaves were examined in relation to nitrogen content (Nc) in rice, winter wheat, maize, soybean, field bean, tomato, potato, and beet. P_sat was positively correlated with Nc as follows: P_sat = CfNc + P_sat0, where Cf and P_sat0 are coefficients. The value of Cf was high in maize, medium in rice and soybean, and low in field bean, potato, tomato, and beet, of which difference was not explained by ribulose-1,5-bisphoshate carboxylase/oxygenase (RuBPCO) content. R_D was explained by P_sat and/or Nc, however, two models must be applied according to plant species. R_D related linearly with P_sat and Nc in maize, field bean, and potato as follows: R_D = a P_sat + b, or R_D = aNc + b, where a, a, b and b are coefficients. In other species, the R_D/P_sat ratio increased exponentially with the decrease of Nc as follows: R_D/P_sat = a exp(b Nc), where a and b are coefficients. Therefore, R_D in these crops was expressed as follows: In(R_D) = ln(a P_sat) + b Nc, indicating that R_D in these crops was regulated by both P_sat and Nc.