Differential response of CO2 uptake parameters of soil- and sand-grown phaseolus vulgaris (L.) plants to absorbed ozone flux.
Shoots of a soil- or sand-grown dwarf bean variety were exposed to O(3) concentrations in the range of 500 to 900 ppb for up to 5 h. The measured exchange rates of water vapor and CO(2) during exposures were used to calculate stomatal and mesophyll conductances averaged across all leaves. Changes in conductances were related to exposure duration and absorbed O(3) totals (AOT). Both conductances were more sensitive to AOT in sand-grown plants, which also had more visible injury under comparable AOT values. Measurements of the relationship between CO(2) exchange and internal CO(2) concentration of single leaflets of treated plants also showed greater sensitivity of CO(2)-saturated photosynthesis in sand-grown plants. Diffusional processes were not likely to have been the cause of dissimilar responses because the O(3) absorption rate was lower in sand-grown plants. A difference in the scaveninng capacities in cells is suggested to be the cause of the differences in sensitivity to acute O(3) exposure.
Moldau
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Institute of Astrophysics and Atmospheric Physics, 202444 Tõravere, Tartu, Estonia.
Kull
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Sõber
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Norby
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RJ