THE EFFECTS OF UV-B RADIATION ON LOBLOLLY-PINE .3. INTERACTION WITH CO2 ENHANCEMENT

Projected depletions in the stratospheric ozone layer will result in increases in solar ultraviolet-B radiation (290-320nm) reaching the earth's surface, These increases will likely occur in concert with other environmental changes such as increases in atmospheric carbon dioxide concentrations. Currently very little information is available on the effectiveness of UV-B radiation within a CO2-enriched atmosphere, and this is especially true for trees. Loblolly pine (Pinus taeda L.) seedlings were grown in a factorial experiment at the Duke University Phytotron with either 0, 8.8 or 13.8 kJ m(-2) of biologically effective UV-B radiation (UV-B-BE) The CO2 concentrations used were 350 and 650 mu mol mol(-1). Measurements of chlorophyll fluorescence were made at 5-week intervals and photosynthetic oxygen evolution and leaf pigments were measured after 22 weeks, prior to harvest. The results of this study demonstrated a clear growth response to CO2 enrichment but neither photosynthetic capacity nor quantum efficiency were altered by CO2. The higher UV-B irradiance reduced total biomass by about 12% at both CO2 levels but biomass partitioning was altered by the interaction of CO2 and UV-B radiation. Dry matter was preferentially allocated to shoot components by UV-B radiation at 350 mu mol mol(-1) CO2 and towards root components at 650 mu mol mol(-1) CO2. These subtle effects on biomass allocation could be important in the future to seedling establishment and competitive interactions in natural as well as agricultural communities.