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Joint Action of Sulfur Dioxide and Nitrogen Dioxide on Foliar Injury and Stomatal Behavior in Soybean¹

ABSTRACT

Six cultivars of soybeans [Clycine max (L.) Merr.] were screened for susceptibility with respect to foliar necrosis after exposure to short-term, relatively high concentrations of SO₂ or SO₂ in combination with NO₂. In all screening trials (three), the combination of SO₂ and NO₂ produced less foliar injury than did the same concentration of SO₂ singly.

Three of the six cultivars with differing susceptibilities to SO₂, ‘Beeson’ (most sensitive), ‘Amsoy’ (intermediate), and ‘Hark’ (least sensitive), were grown to the 10-trifoliate stage and were exposed for 4 hours to charcoal-filtered air (control), 5,200 µg m^–3 SO₂ (2 ppm), 950 µg m^–3 NO₂ (0.5 ppm) or 5,200 µg m^–3 SO₂ plus 950 µg m^–3 NO₂. Again, necrotic lesions developed only on those plants exposed to 5,200 µg m^–3 SO₂ singly. The youngest fully expanded trifoliates on all three cultivars had the most leaf area damaged. Leaf resistance measurements were made on the upper and lower leaf surfaces of the eighth and ninth trifoliates on two of the six plants per cultivar exposed to each treatment. No changes in leaf resistances of the control plants or those exposed to 950 µg m^–3 NO₂ were measured. Leaf resistances increased somewhat during exposure to SO₂, but they increased dramatically in plants exposed to the combination of SO₂ and NO₂. The antagonistic effects of SO₂ and NO₂ on the development of necrotic lesions reported in this paper can be explained at least partially by pollutant avoidance due to stomatal closure caused by the combination of the two pollutants.

Key Words: interaction • antagonism

¹ Contribution from the Boyce Thompson Inst. for Plant Res. at Cornell, Ithaca, NY 14853. This work was supported by the Dep. of Energy, Contract no. EE-77-5-02-4368.

² Research Associate and Program Director, respectively, Environmental Biology Program, Boyce Thompson Inst. for Plant Res. at Cornell, Ithaca, N.Y.

Received for publication February 4, 1980.