A model is presented which aims at quantifying the CO2 and H2O gas exchange of whole plants in their natural microenvironment, the canopy. In an up-scaling approach the model combines leaf (gas exchange, energy balance) and canopy (radiative transfer, wind attenuation) scale simulations. Net photosynthesis and stomatal conductance are modelled using a nitrogen sensitive model of leaf gas exchange. An analytical solution to the energy balance equation is adopted to calculate leaf temperatures. Radiative transfer, separately for the wavebands of photosynthetically active, near-infrared and long-wave radiation, is simulated by means of a model which accounts for multiple scattering of radiation using detailed information on canopy structure as input data. Partial pressures of CO2 and H2O, as well as air temperatures within the canopy are not modelled, but instead, measured values are used as input data. Field studies were carried out at the ECOMONT pilot study area Monte Bondone (Trentino, Italy, 1550 m a.s.l.). The model is parametrised for four forbs and one graminoid species occurring at three sites differing in land use, i.e. an abandoned area, a meadow and a pasture. Independent measurements are used to validate each of the major submodels of the comprehensive whole plant gas exchange model.