Comparison of Photosynthetic Responses to Carbon Dioxide in Pasture Species

Thirteen major pasture species were grown in controlled environments at 3 temperatures (12n, 18/13 and 28/23°C) and at 350 nnd 700 ppm CO2 for 4-8 weeks and net photosynthesis measured under these conditions. In C1 cultivars, short-term (within minutes) exposure to elevated CO2 had the greatest effect on photosynthesis, with an average of 55% higher rates than that at ambient CO2. There was also a response to long-term growth at high CO2, with a,1 average of 40% higher rates of photosynthesis than at ambient CO2 (both measured al their growth CO2) and a marked alteration in the temperature dependence Qf photosynthesis. However, in both the short and long term, there was a continuum of response of photosynthesis to elevated CO2 between the species. Ranking between the cultivars also depended on the growth temperature. In C4 species response lo elevated CO2 was only minor, both in the short and long term. The results indicate considerable variability between the major pasture species in the potential impact of a climate-change-induced increase in CO2•