A nitrogen sensitive model of leaf carbon dioxide and water vapour gas exchange: application to 13 key species from differently managed mountain grassland ecosystems

During the EU-project ECOMONT (Project No. ENV4-CT95-0179), which focuses on effects of land-use changes on mountain ecosystems, an experimental and modelling strategy at the leaf level was developed, which centres on the intimate relationship between leaf nitrogen content and net photosynthesis. Leaf nitrogen content reflects nutrient availability, shows characteristic seasonal dynamics and is of great importance for the analysis of intraspecific variability of gas exchange. The fully parameterised leaf model is capable of predicting net photosynthesis and stomatal conductance for any combination of microclimatic variables as well as any leaf nitrogen content. At the ECOMONT pilot research area Monte Bondone (Trentino/Italy) three grassland sites differing in land-use, a hay meadow, a pasture and an area abandoned since 35 years were selected as study sites. Leaf gas exchange characteristics and nitrogen contents of 13 species were studied and used for parameterising nitrogen sensitive leaf models. Independent data sets, diurnal courses of photosynthesis and stomatal conductance under the prevailing environmental conditions, were used for validation. A sensitivity analysis was performed in order to test the ability of the model to account for changes in leaf nitrogen content, varying leaf nitrogen content together with the environmental driving variables. These leaf models provide the physiological basis for scaling-up gas exchange from the leaf to the whole plant and canopy level and further to the landscape level.