Document: JUL-3-35-30

The effect of ultraviolet-B radiation on photosynthesis and stress tolerance for douglas-fir (Psuedotsuga menziesii) seedlings.

KONVALINKA, J.M.*, R.A.DONAHUE and M.E.POULSON

Idaho State University, Pocatello, Idaho 83209 USA ¹

Abstract:
Douglas-fir is a predominant tree species in the Pacific Northwest that is typically harvested by clear cutting, which produces large forest openings that are replanted with seedlings that have mortality rates up to 80%. These seedlings are typically grown in glasshouses constructed of materials that absorb all or most of the solar ultraviolet-b (UV-B) radiation and are not acclimated to the environmental stresses such as high light, high temperatures and drought present in clear-cut environments. We hypothesize that UV-B in the growth light regime can serve as a signal that can improve stress tolerance and decrease seedling mortality. Douglas-fir seedlings were grown in 100 and 200 moles m^-2 s^-1 PAR with 6 kJ m^-2 d^-1 UV-B_be (UV-B+) and without supplemental UV-B (UV-B). The treatment and control groups were compared by non-destructive measurements of photosynthesis using gas exchange and chlorophyll fluorescence techniques. Destructive growth analyses are currently underway to document differences in morphological, biochemical and growth characteristics. UV-B+ seedlings had from 0-20% higher maximum rates of carbon assimilation (A_max) and an enhanced capacity to down-regulate photochemical efficiency of photosystem II during short-term exposure to photoinhibitory light levels (10 minutes, PAR = 2000 moles m^-2 s^-1). After 4-hours of photoinhibitory treatment, A_max was decreased 25% for both UV-B+ and UV-B seedlings. After a 6-hour dark recovery period, A_max for UV-B+ seedlings recovered to within 5% of control plants while UV-B seedlings only recovered to 20% of controls. These results indicate the UV-B+ seedlings had higher capacity for photosynthesis and stress tolerance in high light. We are currently testing the response of UV-B+ and UV-B seedlings to temperature and water stress. These results will be used to optimize the growth light conditions to enhance stress tolerance for out planted Douglas-fir seedlings.

Keywords: Ultraviolet-B radiation, Douglas-fir, gas exchange, chlorophyll fluorescence,

This abstract is being presented at: 10:30 AM in session:
Poster Session #14: UV-B.