Effects of nitrogen dioxide on biochemical and physiological characteristics of soybean.

One month old soybean (Glycine max (L.) Merrill) cv. 'Williams' plants were exposed to nitrogen dioxide (NO2 at 0.1, 0.2, 0.3, and 0.5 microl liter(-1) and carbon filtered air (control), 7 h per day for five days, under controlled environment. Data were collected on net photosynthetic rate (PN), stomatal resistance (SR), and dark respiration rate (DR), immediately following the fifth day of exposure and 24 h after termination of exposure. Chlorophyll a (Ch a), chlorophyll b (Ch b), total chlorophyll (tot Ch) and foliar nitrogen (N) were measured before and after exposures. Growth characteristics--relative growth rate (RGR), net assimilation rate (NAR), leaf area ratio (LAR), and root shoot ratio (RSR) -- were computed for treated plants using standard growth equations. Increases of 18% and 23% in PN were observed immediately following exposure to 0.2 microl liter(-1) NO2 and after 24 h recovery period, respectively. With 0.5 microl liter(-1) NO2 treatment, reductions in PN of 23% and 50% were observed, immediately after exposure and following 24 h recovery, respectively. DR rates with 0.2 l liter(-1) treatment were higher than the control. Chlorophyll a and tot Ch showed significant reduction with 0.5 microl liter(-1) NO2 treatment. The percent reduction in Ch a and tot Ch with 0.5 microl liter(-1) NO2 were 45% and 47%, respectively. Increases in foliar nitrogen content after 0.2 and 0.3 microl liter(-1) NO2 treatments were 46% and 69%, respectively. Nitrogen dioxide at 0.5 microl liter(-1) reduced RGR and NAR by 47% and 51%, respectively. Leaf area ratio was 42% higher in 0.5 microl liter(-)1 NO2 treated plants, compared with the control; this increase was insufficient to compensate for the decrease in NAR resulting in a net decline in RGR. Nitrogen dioxide up to 0.2 microl liter(-1) increased PN and foliar-N content of soybean. With 0.5 microl liter(-1) NO2, significant decreases were observed in PN, leaf chlorophyll, foliar-N, NAR and RGR. Nitrogen dioxide up to 0.2 microl liter(-)1 has a favorable influence on overall growth characteristics of soybean; however, inhibitory effects were seen with NO2 treatment at 0.5 microl liter(-1).