Dynamics of photosynthesis in pine stands

The CO2 exchange of pine (Pinus sylvestris L.) shoots was continuously monitored over several years. The spatial and temporal variability of gas exchange was thoroughly investigated for three forest types. The net uptake of CO2 by current-season shoots in a bilberry pine stand equaled 5.4 g CO2 per g dry wt for the growing season. The net CO2 assimilation by one-year-old shoots over a growing season constituted 9.9 and 2.4 g CO2/(g dry wt year) in the upper and lower crown parts, respectively. The nighttime respiration of the current-season shoots released 0.7 g CO2/(g dry wt year), and the respiration of one-year-old shoots in the upper and lower parts of the canopy released 0.45 and 0.36 g CO2/(g dry wt year), respectively. Recalculation of three-year data per entire crown yielded an annual average carbon assimilation of 1.54 g C/(g dry wt year). Water relations markedly affected CO2 fixation. Nevertheless, the daily average values of photosynthesis in the summer were similar for pine stands with bilberry, heather, and dwarf shrub–polytric as understory dominants. It is shown that the realization of changes in photosynthetic function is related in time to growth processes.