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Nitrogen Dioxide Effects on Photosynthesis in Soybean

Dep. of Natural Sciences, The Univ. of Maryland, Eastern Shore Campus, Princess Ann, MD 21853;

Charles Mulchi

Dep. of Agronomy, Univ. of Maryland, College Park, MD 20742.

^* Corresponding author.

ABSTRACT

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.

Key Words: Glycine max (L.) Merr. • Air pollution • Net photosynthetic rate • Dark respiration rate • Stomatal resistance

Contribution from the Dep. of Agric. Sci., Univ. of Maryland Eastern Shore, Princess Anne, MD.

Received for publication June 25, 1987.