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Effects of Sulfur Dioxide on Nitrogen Fixation, Carbon Partitioning, and Yield Components in Snapbean¹

ABSTRACT

The air pollutant SO₂ is known to affect plant biochemistry and physiology, although very little is known about its effects on N₂-fixation in legumes. This study sought to determine if N₂-fixation, C partitioning, and plant productivity of snapbean (Phaseolus vulgaris L.) were affected under short-term, low-level SO₂ exposures. Plants were exposed, 29 d after planting (7 d before anthesis), to 0, 18, and 36 µmol SO₂ m^–3 for 4 h d^–1 for 5 d in a fumigation chamber. On the last day of SO₂ treatment, plants were also exposed to ¹⁴CO₂ to determine changes in C partitioning patterns. At these concentrations, there was no visible damage to plant tissue and no significant changes in dry weight or yield components. Only the 36 µmol SO₂ m^–3 treatment reduced C₂H₂ reduction rates, but recovery to near control rates occurred within 24 h after SO₂ removal. Leaves of plants treated with 18 µmol SO₂ m^–3 exported more of their total assimilated ¹⁴C than control plants, while those treated with 36 µmol SO₂ m^–3 retained greater amounts. Retention of ¹⁴C at the 36 µmol SO₂ m^–3 level may account for the inhibition of C₂H₂-reduction because of less photosynthate arriving at the root nodules. These data suggest that SO₂ levels that do not cause visible injury may interfere with C metabolism and transport in snapbean.

Key Words: photosynthate partitioning • transport • C₂H₂reduction • nodules • Phaseolus vulgaris L.

¹ Contribution from the Plant Science Dep., Utah State Univ., Logan, U 84322. Utah Agric. Exp. Stn. Journal Paper no. 3254.

² Former Graduate Assistant, now Postdoctoral Research Associate, Dep. of Agronomy and Plant Genetics, Univ. of Minnesota, St. Paul, MN, and Professor of Crop Physiology, Dep. of Plant Science, Utah State Univ., Logan, UT.

Received for publication September 23, 1985.