1985. Effects of low concentrations of O3, leaf age and water stress on leaf diffusive conductance and water use efficiency in soybean. -Physiol. Plant. 63: 5&-64.Ozone, leaf age and water stress each affected leaf conductance in soybean [Glycine max (L.) Merr. Hodgson], but there were no mteractions among these factors. Exposure to increased concentrations of O, (0.01, 0.05, 0.09. aod 0.13 nl 1"' ) resulted in linear declines in abaxial and adaxial conductances io leaves of all ages. There were no differences in relative response to O3 between the two leaf surfaces. For well-watered plants, water use efficiency also decreased with exposure to increased O, cooceotrations (water-stressed plants were not tested). Abaxial conductance increased as leaves aged from 4 to 10 days and then declioed with further aging. Adaxial conductance decreased with all increases in leaf age beyond 4 days, and the ratio of abaxial/adaxial conductance increased continuously throughout the leaf lifespan. During water-stress cycles (water withheld for 2-3 days) leaves of water-stressed plants had tower conductances than those from well-watered plants, and there was no difference in relative response between abaxial and adaxial stomata.Additional key words -Abaxial, adaxial, stomata. (reprint requests), et al.,
P. B. Reich