Nitrogen Nutrition and Photosynthesis in Sugar Beet (Beta vulgaris L.)1

Nitrogen deficiency was evaluated as an ecological factor affecting CO2 assimilation in sugar beet (Beta vulgaris L.) leaves. Nitrogen deficiency reduced the chlorophyll concentration and photochemical capacity of the older leaves but not of young and recently mature leaves. The maximum rate of photosynthesis was reduced in leaves of all ages. This was correlated with a smaller leaf protein content and with an increase in CO2 diffusion resistances. Although the rate of photosynthesis was reduced as much as 40% when plants were grown for 14 days without nitrogen, the effects were reversible, and activity could be restored to the normal rate within 4 days by adding nitrate nitrogen to the deficient nutrient solution.