The influence of exposure temperature and relative humidity on the response of pinto bean foliage to sulfur dioxide

When 20-day-old pinto bean plants (Phaseolus vulgaris 'Pinto III') were exposed to 0.9 ppm sulfur dioxide (SO₂) the amount of trifoliolate leaf injury induced by SO₂ generally was greater at 32C than at either 13 or 21 C, and greater at 80% relative humidity (RH) than at 40 and 60% RH. However, injury was less following exposures at 32 C for 1 hr and 21 C for 1 and 2 hr than that caused by equivalent exposures at 13 C. Stomatal conductance increased significantly with increased temperature and RH. Stomatal conductance of trifoliolates leaves from plants exposed to SO₂ was less than that of exposed control plants. The foliar content of SO₂, evaluated after exposures at 21 and 32 C, generally was greater at the higher temperatures.