APPLICATION OF THE GENERALIZED RABINOWITCH MODEL TO ANALYSIS OF PICEA-ABIES PHOTOSYNTHESIS AS A FUNCTION OF LIGHT, TEMPERATURE, AND HUMIDITY

The rate of assimilation (A) was measured in intact spruce twigs (seco nd- and third-order branches) that were developed during the current a nd previous growth periods. Measurements were performed under variable levels of irradiance (I), temperature (T), and deficit of water vapor pressure (D). These measurements yielded 425 values of A(I, T, D) in all. Based on the data obtained, a quantitative physiological model wa s developed that explicitly describes the dependence of assimilation o n the aforementioned environmental factors. The model includes the sto matal conductance g,(I, T, D). Some parameters were taken from the lit erature, others were found by fitting the model to empirical data. Num erical experiments were performed in order to determine the number of model parameters that can be obtained by fitting. The present model an d the available data allow the determination of two or three parameter s, depending on the age and density of the spruce needles. The quantum efficiency (alpha = 0.012-0.020) and the maximum assimilation rate (A (max) = 2.5-5.7 mu mol/(m(2) s)) are the most firmly determined.