Effects of ultraviolet‐B irradiation on plants during mild water stress.

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Abstract
Cucumber (Cucumis sativus L. cv. Delikatess) and radish (Raphanus sativus L. cv. Saxa Treib) were grown in a factorial design under two ultraviolet‐B (UV–B) irradiances and three levels of water stress. On a weighted, daily dose basis the UV–B radiation treatments were equivalent to ambient levels during the beginning of the growing season (controls) and those predicted for an 11.6% ozone depletion during the summer solstice at 49°N latitude. Water stress was achieved by varying the frequency of watering. The combination of UV–B radiation and water stress resulted in large species differences in the pattern of stomatal resistances. This study indicated that Cucumis is one of the most sensitive crop species to UV–B radiation yet identified and that the primary effect of UV–B radiation in this species is a decrease in the leaf diffusive resistance to water vapor. This, therefore, may result in reductions in growth via increased water stress.