INTERACTIONS BETWEEN ELEVATED CO2 CONCENTRATION, NITROGEN AND WATER -EFFECTS ON GROWTH AND WATER-USE OF 6 PERENNIAL PLANT-SPECIES

Two experiments are described in which plants of six species mere grow n for one full season in greenhouse compartments with 350 or 560 mu mo l mol(-1) COL. In the first experiment two levels of nitrogen supply w ere applied to study the interaction between CO2 and nitrogen, In the second experiment two levels of mater supply were added to the experim ental set-up to investigate the three-way interaction between CO2, nit rogen and water, Biomass and biomass distribution were determined at h arvests, while water use and soil moisture were monitored throughout t he experiments, In both experiments a positive effect of CO2 on growth was found at high nitrogen concentrations but not at low nitrogen con centrations, However, plants used much less water in the presence of l ow nitrogen concentrations, Drought stress increased the relative effe ct of elevated CO2 on growth, Available soil moisture was used more sl owly at high CO2 during drought or at high nitrogen concentrations, wh ile 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 a ppeared to respond better to high CO2 when supplied with a high level of nitrogen, inherently slow-growing species were more successful at l ow nitrogen concentrations.