Document: STE-3-29-25

Plants grown in shade are sensitive to even low levels of ultraviolet-B radiation.

FLINT, S.D.* and M.M.CALDWELL

Utah State University, Logan, UT 84322 USA ¹

Abstract:
A critical question in ultraviolet-B radiation research is how different portions of the solar spectrum influence plant UV-B sensitivity. Field-grown plants show only subtle responses to supplemental UV-B, yet plants grown under low visible light (as in most growth chambers and greenhouses) show much more discernible changes. Plants often grow in shade of neighbors, and shade light is proportionately higher in UV-B than is open sunlight. Thus, the influence of different portions of the spectrum under shade is a potentially important issue. Since this topic has seldom been addressed with realistic light levels, we examined this in three simultaneous field experiments using Setaria viridis, green foxtail, a weedy summer-annual grass of both open and shaded habitats. The first experiment had supplemental UV-B simulating a 30% ozone depletion in full sunlight; the second had both visible light and UV-B radiation reduced to 35% of that in the first experiment using shade cloth; and the third had the same level of visible radiation as the second, but double the UV-B. In the first experiment, simulating ozone depletion under open sunlight conditions, only transitory growth inhibition was seen early in the experiment. In the two shade experiments, UV-B reduced plant height, leaf length, and stem internode elongation 10-15%, and mass by 10%, suggesting that plants in shade are more sensitive to UV-B, even if the UV-B has been reduced by the same proportion as the visible light. Surprisingly, increasing UV-B to simulate natural shade (Experiment 3) increased the magnitude of the UV-B effects by several percent only in the early part of the experiment.

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This abstract is being presented at: 8:15 AM in session:
Oral Session #69: UV-B.