Competitive Interaction in Plant Populations Exposed to Enhanced UV-B Radiation

Competitive balance and changes in individual plant growth parameters of eight pairs of plant species exposed to enhanced UV-B irradiation were determined under field conditions simulating ozone reductions of about 0.08 atm·cm. The levels of irradiance represented ozone decreases of about 25-30 percent from approximate ambient ozone concentrations for high solar altitudes on clear days during the study. A method for calculating and statistically analyzing relative crowding coefficients was developed and used to evaluate the competitive status of the species pairs sown in a modified replacement series. The effect of UV-B irradiance was generally detrimental to plant growth, and was reflected in decreased leaf area, biomass, height and density as well as changes in competitive balance for various species. For some species inter-specific competition apparently accentuated the effect of UV-B radiation, while intensive intraspecific competition may have had the same effect for other species