Parametrization of two photosynthesis models at the canopy scale in a northern boreal Scots pine forest

In this work, eddy covariance data from a northern boreal Scots pine (Pinus sylvestris) stand were used in the parametrization of two up-scaled leaf-level photosynthesis models. The parametrization was carried out by eddy covariance data inversion. The biochemically based Farquhar model parameters, the maximum rate of electron transport (J(max)) and maximum rate of carboxylation [V-c(max)], were both obtained from the temperature responses measured by the eddy covariance. The semi-empirical model, based on optimizing water use and carbon gain, was parametrized according to the seasonal behaviour of the parameter ss. The parametrization of the models was performed for the year 2001, while 2002 was used as a test year to study the models' capabilities. Both of the models tracked daily CO2 assimilation fairly well, reaching the high growing-season rates in mid-June and starting the autumn drawdown at the beginning of September. The incapability of the models to track the diminishing Of CO2 fluxes during very dry days brings up the issue of combining a soil model into the canopy model. The biochemical model parameters have temperature responses that change during the growing season. The biochemical model responds more to the temperature, whereas the semi-empirical model is strongly driven by the light level.