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 (355Kb)
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30,369,000 Yen
To investigate the effects of enhanced UV-B radiation caused by stratospheric ozone depletion on plants, three cucumber cultivars and 17 rice cultivars were irradiated for 3 weeks in sun-lit environmental glass chambers and for 2 months in the fields under UV-B(290-320nm) irradiation from fluorescent sunlamps using 0.10mm polyvinyl chloride or cellulose acetate films and UV-B free control conditions using 0.10mm polyester film. In the sun-lit environmental glass chambers, cucumber plants were irradiated with three levels (0.244 and 381 mW m-2) of biologically effective UV-B(UV-BBE) for 8h(8 a.m. to 4 p.m.) a day. The levels of UV-BBE irradiance at Tsukuba(36゜N latitude) were about 200 mW m-2 at noon in summer under clear sky conditions. Visible foliar injury(yellow lesions and glazing) due to UV-B irradiation occurred on the leaf surface. The leaf area and dry weight of whole plants of the three cultivars of cucumber were significantly reduced and decreased with increasing intensities of UV-BBE irradiation. Growth parameters of the relative growth rate(RGR), the net assimilation rate(NAR) and leaf area ratio(LAR) were reduced by medium and high UV-BBE irradiation throughout irradiation periods. Specific leaf area(SLA) decreased remarkably due to UV-B, which indicates that plants exposed to UV-B increase their leaf thickness. This increase of leaf thickness might be an adaptation mechanism against increased UV-B radiation. On the other hand, in the field experiments, rice plants were irradiated at a predefined proportion(1.5 times control plots) to the global solar UV-B radiation from August 25 to October 23, 1992 by UV irradiation modulation system. No significant influence of UV-B radiation was detected on any growth parameters studied in all the cultivars.
Cucumber, Growth reduction, Injury symptoms, Rice, UV-B