Effects of SO 2 on stomatal conductance and growth of Phaseolus vulgaris

Abstract

Exposure of intact pinto beans Phaseolus vulgaris L. and those with cotyledons removed immediately after germination to 0·15, 0·25 and 0·50 ml litre −1 SO 2 at an identical dose (0·5 ml litre −1 h −1 day −1) for four weeks reduced leaf area, shoot and root dry weights and increased shoot/root ratios and specific leaf areas in all exposed plants. Bean plants with cotyledons removed were smaller than intact plants, but responses to SO 2 were similar in both groups. Increasing the concentration of SO 2 reduced growth to a greater degree than increasing the duration of exposure. Stomatal conductances decreased immediately after exposure as a function of increased concentration of SO 2 but conductances returned to control levels one day after termination of exposures. Reductions in stomatal conductance in response to SO 2 were proportional to reductions in plant growth. These results support the concept that SO 2 at dosages below levels at which foliar injury symptoms develop can decrease stomatal conductance, reduce plant growth and alter partitioning of dry matter into leaves, shoots and roots. These results do not support the contention that slower growing plants show greater growth responses to SO 2 than more rapidly developing plants.