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

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Abstract
The influence of nutrient nitrate level (0-20 millimolar) on the effects of NO2 (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 NO2 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 NO2. The NO2 exposure increased nitrate concentration in roots only at 20 millimolar nutrient nitrate. Exposure to NO2 markedly increased Kjeldahl N concentration in roots but generally decreased that in shoots. The experiments demonstrated that nutrient N level and NO2 concentration act jointly in affecting nodulation and N fixing capability, plant growth and composition, and root/shoot relationships of bean plants.