Effects of Nitrogen Dioxide and Nitrate Nutrition on Nodulation, Nitrogenase Activity, Growth, and Nitrogen Content of Bean 1

The influence of nutrient nitrate level (0-20 millimolar) on the effects of NO 2 (0-0.5 parts per million) on nodulation and in vivo acetylene reduction activity of the roots and on growth and nitrate and Kjeldahl N concentration in shoots was studied in bean ( Phaseolus vulgaris L. cv Kinghorn Wax) plants. Exposing 8-day old seedlings for 6 hours each day, for 15 days, to 0.02 to 0.5 parts per million NO 2 decreased total nodule weight at 0 and 1 millimolar nitrate, and nitrogenase (acetylene reduction) activity at all concentrations of nitrate. The pollutant had little effect on root fresh or dry weights. Shoot growth was inhibited by NO 2 . The NO 2 exposure increased nitrate concentration in roots only at 20 millimolar nutrient nitrate. Exposure to NO 2 markedly increased Kjeldahl N concentration in roots but generally decreased that in shoots. The experiments demonstrated that nutrient N level and NO 2 concentration act jointly in affecting nodulation and N fixing capability, plant growth and composition, and root/shoot relationships of bean plants.