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

Abstract

AbstractThe 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.