PARENT SESSION
Poster Session #50: Climate Change.
Thursday, August 8. Presentation from 8:00 AM to 9:30 AM. Exhibit Hall B & C, TCC

Plant responses to four levels of sub-ambient UV-B radiation: investigating the saturation hypothesis.

Coleman, Robert^*,1, Day, Thomas¹, ¹ Arizona State University, Tempe, Arizona

ABSTRACT- Ambient levels of ultraviolet-B radiation (280-315 nm) induce numerous plant responses including greater leaf concentrations of phenolic compounds yielding increased epidermal UV-B screening, and occasionally, reductions in plant growth. In contrast, plant responses to above-ambient levels of UV-B tend to be more subtle, and in many cases, these plant responses are not observed. It has been proposed that plants are less responsive to increases in solar UV-B beyond ambient levels because targets or mechanisms become saturated. To provide a partial test of this idea, we examined how plant growth, leaf screening effectiveness and screening compound concentrations in Glycine max, Gossypium hirsutum, and Sorghum bicolor changed as UV-B dose approached ambient levels. Ambient UV-B levels were reduced with Teflon sheets covered with strips of Mylar, to levels approximating 91, 84, 71, 55, and 36% of biologically effective UV-B during late winter and early spring in central Arizona. In general, as UV-B dose approached ambient levels, responsive growth parameters and leaf epidermal UV-B transmittance decreased, although responses were species specific. Plant responses to increasing doses of UV-B tended to be non-linear and became less distinct as UV radiation approached ambient levels. Our findings lend some support to the idea that plant responses to UV-B become saturated as doses approach ambient levels.

KEY WORDS: ultraviolet-B radiation, ozone depletion, leaf screening, growth response