Source of nitrogen nutrition affects pea growth involving changes in stomatal conductance and photorespiration

The effect of the source of nitrogen (N) nutrition [N-2 fixation and nitrate (NO3) assimilation] on plant productivity, gas exchange, N assimilation, water relations, and glycollate oxidase activity were studied in pea plants. Nitrogen-fixing plants showed a higher RGR over the study period. This higher RGR was correlated with higher stomatal conductance and, consequently, a higher transpiration rate. Photosynthetic N-use efficiency was also higher when plants were nodulated. We found glycollate oxidase activity, a key enzyme of the photorespiratory pathway, much lower in N,fixing plants, what strongly suggests that energy losses due to photorespiration are lower in these plants, and therefore, photosynthetic efficiency was higher.