Assessing seasonality of biochemical COsub2/sub exchange model parameters from micrometeorological flux observations at boreal coniferous forest

摘要

The seasonality of the NEE of the northern boreal coniferous forests wasinvestigated by means of inversion modelling using eddy covariance data.Eddy covariance data was used to optimize the biochemical model parameters.Our study sites consisted of three Scots pine (l. Pinus sylvestris) forests and one Norwayspruce (l. Picea abies) forest that were located in Finland and Sweden. We obtainedtemperature and seasonal dependence for the biochemical model parameters:the maximum rate of carboxylation (V_c(max)) and the maximum rate ofelectron transport (J_max). Both of the parameters were optimized withoutassumptions about their mutual magnitude. The values obtained for thebiochemical model parameters were similar at all the sites during summertime. To describe seasonality, different temperature fits were made for thespring, summer and autumn periods. During summer, average J_max across thesites was 54.0 μmol m−2 s−1 (variance 31.2 μmol m−2 s−1)and V_c(max) was 12.0 μmol m−2 s−1 (variance 6.6 μmol m−2 s−1)at 17°C. The sensitivity of the model to LAI and atmospheric soil water stress was also studied. The impact ofseasonality on annual GPP was 17% when only summertime parameterizationwas used throughout the year compared to seasonally changingparameterizations.