Interaction of Elevated Ultraviolet-B Radiation and CO2 on Productivity and Photosynthetic Characteristics in Wheat, Rice, and Soybean

Wheat (Triticum aestivum L. cv Bannock), rice (Oryza sativa L. cv IR-36), and soybean (Glycine max [L.] Merr cv Essex) were grown in a factorial greenhouse experiment to determine if CO(2)-induced increases in photosynthesis, biomass, and yield are modified by increases in ultraviolet (UV)-B radiation corresponding to stratospheric ozone depletion. The experimental conditions simulated were: (a) an increase in CO(2) concentration from 350 to 650 microliters per liter; (b) an increase in UV-B radiation corresponding to a 10% ozone depletion at the equator; and (c) a and b in combination. Seed yield and total biomass increased significantly with elevated CO(2) in all three species when compared to the control. However, with concurrent increases in UV-B and CO(2), no increase in either seed yield (wheat and rice) or total biomass (rice) was observed with respect to the control. In contrast, CO(2)-induced increases in seed yield and total plant biomass were maintained or increased in soybean within the elevated CO(2), UV-B environment. Whole leaf gas exchange indicated a significant increase in photosynthesis, apparent quantum efficiency (AQE) and water-use-efficiency (WUE) with elevated CO(2) in all 3 species. Including elevated UV-B radiation with high CO(2) eliminated the effect of high CO(2) on photosynthesis and WUE in rice and the increase in AQE associated with high CO(2) in all species. Elevated CO(2) did not change the apparent carboxylation efficiency (ACE) in the three species although the combination of elevated CO(2) and UV-B reduced ACE in wheat and rice. The results of this experiment illustrate that increased UV-B radiation may modify CO(2)-induced increases in biomass, seed yield and photosynthetic parameters and suggest that available data may not adequately characterize the potential effect of future, simultaneous changes in CO(2) concentration and UV-B radiation.