Two experiments are described in which plants of six species were grown for one full season in greenhouse compartments with 350 or 560 μmol mol–1 CO2. In the first experiment two levels of nitrogen supply were applied to study the interaction between CO2 and nitrogen. In the second experiment two levels of water supply were added to the experimental set-up to investigate the three-way interaction between CO2, nitrogen and water. Biomass and biomass distribution were determined at harvests, while water use and soil moisture were monitored throughout the experiments. In both experiments a positive effect of CO2 on growth was found at high nitrogen concentrations but not at low nitrogen concentrations. However, plants used much less water in the presence of low nitrogen concentrations. Drought stress increased the relative effect of elevated CO2 on growth. Available soil moisture was used more slowly at high CO2 during drought or at high nitrogen concentrations, while at low nitrogen concentrations decreased water use resulted in an increase in soil moisture. The response to the treatments was similar in all the species used. Although potentially faster growing species appeared to respond better to high CO2 when supplied with a high level of nitrogen, inherently slow-growing species were more successful at low nitrogen concentrations.