Competition in a Global Change Environment: The Importance of Different Plant Traits for Competitive Success

Plant traits of both structural and physiological nature have been reported to play an important role in the outcome of a competitive interaction. In this experiment a survey of the importance of characteristics such as height, leaf area and vertical distribution, leaf inclination, light transmission through a leaf and through the canopy together with leaf photosynthesis rates, was made for two grasses: Lolium perenne L. and Festuca arundinacea Schreb. Both species were grown in a competitive set-up with minimal belowground interactions under four different global change conditions of CO2 concentration and air temperature (ambient, elevated CO2 concentration 700 ,umol mol-1, increased air temperature + 4?C, combined) in naturally sunlit air-conditioned half-open plastic greenhouses. Plants were grown for a whole growing season with regular (every 4 weeks) clippings at 3.5 cm height. Results demonstrate that Lolium has a much greater competitive ability when compared to Festuca (aggressivity = 0.465). This may be a consequence of the slightly higher leaf photosynthesis rates (+ 15%) in combination with a