Peculiarities of Siberian fir photosynthesis model as a result of plant adaptation to environmental conditions

Siberian fir (Abies sibirica Ledeb.) is one of the main forest-forming species of northeastern European Russia. Compared to other forest-forming species, Siberian fir is poorly studied and there are no integral models describing the dynamics of fir photosynthesis depending on environmental factors and growing conditions. Modeling of intensity of fir photosynthesis depending on vertical gradients of environmental factors and anatomo-morphological structure of Siberian fir needles varying from the location within the vegetation canopy by height is the purpose of the present study. The study was conducted in the middle taiga subzone of the Komi Republic in a bilberry-sphagnum spruce forest at two altitudinal levels. The objects of the study are represented by two Siberian fir trees occupying different positions in the stand structure, one being a part of the main tier, the other being a part of the second tier. The CO₂ assimilation rate of fir needles, the intensity of incident photosynthetically active radiation, air temperature, relative air humidity, and atmospheric CO₂ concentration were measured in the crowns of selected trees on uncut shoots; the anatomical and morphological structure of fir needles depending on their height position in the stand structure was studied. A regression equation modeling the dependence of CO₂ assimilation rate by Siberian fir needles on environmental factors was obtained on the basis of experimental data. Validation showed the adequacy and statistical significance of the model. Specificity of the model and anatomo-morphological features of Siberian fir needles depending on their height in the stand was revealed.