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Ultraviolet Radiation Reflectance, Transmittance, and Absorptance by Plant Leaf Epidermises¹

Partial destruction of ozone in the earth's upper atmosphere (stratosphere) will increase levels of ultraviolet (UV) radiation that reach the earth's surface; consequently, plants could be exposed to harmful amounts of UV-B radiation (280 to 320 nm). The objective of our research was to characterize the reflectance, transmittance, and absorptance of UV-B radiation by leaf epidermises. Accordingly, measurements were made spectrophotometrically over the 260 to 360-nm wavelength, to encompass the UV-B waveband, on epidermises of different thicknesses from six plant genera: Century plant (Agave americana L.), onion bulb (Allium cepa L.), peperomia (Peperomia obtusifolia A. Dietr.), yucca (Yucca treculeana Carr.), kalanchoe (Kalanchoe laciniata DC.), and pricklypear (Opuntia lindheimeri Engelm.).

Thick epidermises of pricklypear, peperomia, century plant, and yucca reflected and transmitted less and absorbed more UV radiation over the 260 to 360-nm waveband than thinner epidermises of onion and kalanchoe. Absorptance of the critical UV-B radiation ranged from 91 to 96% for the thick epidermises and from O to 66% for the thinner epidermises.

It is concluded that leaves of plants with thick epidermises would have less internal damage to inner tissues of their mesophylls by UV-B radiation than leaves with thinner epidermises; however, UV-B radiation may damage the epidermis itself.

Key Words: UV-B radiation • Ozone • Stratosphere

² Plant Physiologist and Biological Technicians, respectively, USDA, Weslaco, TX 78596.

Received for publication July 11, 1974.