Carbon Dioxide Uptake in Nitrogen‐Deficient Plants¹

Carbon dioxide uptake at the leaf surface in air and in oxygen‐free air was examined in maize ( Zea mays L.), cotton ( Gossypium hirsutum L.), and bean ( Phaseolus vulgaris L.) plants exposed to an increasing deficiency of nitrogen. Carbon assimilation in these conditions was then related to the stomatal and apparent mesophyll resistances to CO 2 transfer. Lack of nitrogen decreased carbon assimilation in all three species. Assimilation was enhanced in oxygen‐free air in cotton and beans, but little affected in maize. The inhibition of assimilation in nitrogen‐deficient plants was accompanied by an apparent increase in mesophyll resistance to CO 2 transfer, but some increase in stomatal resistance was also measured. Enhancement of carbon assimilation in oxygen‐free air was negatively associated with the apparent mesophyll resistance to CO 2 transfer. Such apparent resistances in the mesophyll may be associated with differences in dark reactions, with a light or photosynthetically‐induced respiratory pathway, as well as with CO 2 diffusion.