Nitrogen Dioxide Effects on Photosynthesis in Soybean
- Sashikala Sabaratnam,
- Gian Gupta * and
- Charles Mulchi
Very little information is available on the effects of nitrogen dioxide (NO2) on photosynthesis in soybean [Glycine max (L.) Merr.]. This investigation was undertaken to study the effects of NO2 (0.0, 0.1, 0.2, 0.3, and 0.5 µL/L) on net photosynthetic rate (PN), stomatal resistance (SR), and dark respiration rate (DR) of soybean cultivar Williams treated 7 h/d, for 5 d in a controlled environment. Measurements of PN, SR, and DR were made both immediately and 24 h after the termination of exposure, using a LICOR 6000 Portable Photosynthesis system. Treatment effects on PN and DR were statistically significant. Increases of 18 and 23% in PN were observed immediately following exposure to 0.2 µL/L NO2 and after a 24-h recovery period. With the 0.5 µL/L NO2 treatment reductions in the PN of 23 and 50% were observed immediately after exposure and following the 24-h recovery period. Dark respiration rates of leaves treated with NO2, 0.2 µL/L, were 13 and 46% higher than the control immediately after the exposure and after the 24 h recovery. Exposure to 0.2 µL/L of NO2 had a stimulating effect whereas 0.5 µL/L of NO2 inhibited photosynthesis in soybean.
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