Atmospheric nitrogen dioxide at different concentrations levels regulates growth and photosynthesis of tobacco plants

Nitrogen dioxide (NO2) is recognized as a toxic gaseous pollutant. However, an appropriate concentration of NO2 can promote the growth of plants. In this study, tobacco was exposed to different concentrations of NO2. The results that 1, 4, and 8 mu L L-1 NO2 fumigation increased the net photosynthetic rate (P (n)), maximum photochemical efficiency (F (v)/F (m)) and light energy utilization capacity parameters (PI (ABS)) of leaves, and promoted the growth of seedlings. About 16 mu L L-1 NO2 caused the leaves to wither, and the plants were about to die after five days of fumigation. About 8 mu L L-1 NO2 obviously promoted the growth of plants, but meanwhile, the old leaves began to show signs of damage, such as bruising and yellowing. Therefore, 8 mu L L-1 may be the threshold concentration of herbaceous plants with high NO2 assimilation ability. At an intermediate concentration (4 mu L L-1) within the threshold range, NO2 is most beneficial to the growth of herbaceous plants.