Effects of elevated carbon dioxide concentrations on agricultural grassland production

Open-top chambers have been used on a field-grown perennial ryegrass (Lolium perenne) sward to investigate the long-term responses to elevated CO2 concentrations. A concentration of 2 x ambient CO2 increased annual harvestable yield by about 20%, but the proportional stimulation was not constant throughout the growing season nor from one season to the next. Other effects of elevated CO2 were an increase in carbon/nitrogen ratio of tissues and a decrease in specific leaf area and canopy conductance. There was no effect of CO2 on the digestibility of the harvested grass. It is likely that climate change during the next century will lead to significant increases in agricultural grassland production in northern Europe. Production will be stimulated by a direct fertiliser effect due to the increasing CO2 concentration of the atmosphere.