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

Abstract

In thiswork, 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 β 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.