The Swiss ICAT project, currently underway at the Birmensdorf open-top chamber facility, aims at investigating the biological effects of both elevated CO₂ and nitrogen deposition on model ecosystems composed of provenances and clones of young spruce and beech trees as well as an understory of four herbaceous species and ivy. The plants are growing in natural unfertilized forest soils taken from two sites (acidic and calcareous) and transferred into 32 lysimeters, each with a ground area of 3 m². The model ecosystems were established in fall 1994. Beginning at the end of January 1995, these communities were exposed to either ambient or elevated CO₂ (ambient + 200 µl 1⁻¹) concentrations and 5 or 50 kg N ha⁻¹a⁻¹ wet deposition. Emphasis is on understanding ecosystem level responses and their explanation by downscaling to plant and cell level reactions. The multidisciplinary project team will investigate the carbon, water and nutrient cycle.