A MODEL OF THE GAS-EXCHANGE RESPONSE OF PICEA-ABIES TO HABITAT CONDITIONS

Databases describing branch gas exchange of Picea abies L. at two mont ane forest sites, Lageren, Switzerland (National Forschungsprojekt 14 of the Schweizerische Nationalfonds) and Oberwarmensteinach, Germany ( Bayerische Forschungsgruppe Forsttoxikologie), were analyzed in conjun ction with a physiologically based model. Parameter estimates for desc ribing carboxylase kinetics, electron transport, and stomatal function were derived, utilizing information from both single factor dependenc ies and diurnal time course measurements of gas exchange. Data subsets were used for testing the model at the branch level. Most of the obse rved variation in gas exchange characteristics can be explained with t he model, while a number of systematic errors remain unexplained. Fact ors seen as contributing to the unexplained residual variation and not included in the model are light acclimation, degree of damage in adju stment to pollutant deposition, needle age, and cold stress effects. N evertheless, a set of parameter values has been obtained for general a pplication with spruce, e.g., for use in calculating canopy flux rates and to aid in planning of focused leaf and canopy level experiments. The value of the model for estimating fluxes between the forest and th e atmosphere must be evaluated together with measurements at the stand level.