Effects of carbon dioxide concentrations on three grass species grown in mixture in two soil types at different ozone concentrations or temperatures

A seed mixture of Phleum pratense L., Lolium perenne L. and Festuca pratensis Huds. was grown in spaghnum peat or sandy soil in six growth chambers placed in a greenhouse compartment. Two different experiments were performed. Increasing the CO2 concentration from 375 to 740 mu mol mol(-1) increased the total dry weight of the grass mixture by about 30%, while an increase in the O-3 concentration from < 10 to 50 nmol mol(-1) decreased the dry weight by 18% as a mean in both experiments. The relative dry weights of the three species were not significantly affected by elevated CO2 concentrations at low O-3, while Lolium increased its relative dry weight at high O-3 concentrations at low CO2 on the expenditure of Phleum dry weight. CO2 enrichment counteracted some of this O-3 effect. No significant interaction between CO2 concentration and temperature (14 and 19 degrees C mean temperature) was found with respect to the dry weights of the three species. The soil type had generally no influence on the effect of CO2 and O-3. However, plant growth was significantly slower in sandy soil than in peat.