Net Photosynthetic Response to Light Intensity of Shoots from Different Crown Positions and Age in Picea abies (L.) Karst.

Carbon dioxide uptake response to light intensity of detached shoots of open-and forest-grown Norway spruces was investigated in controlled standard conditions. The initial slope of the CO2 uptake light response curve, calculated on leaf area basis and the internal conductance, calculated on leaf weight basis were almost constant for shoots from different positions in the forest canopy. In open-grown trees the maximum photosynthesis and internal conductance (on leaf weight basis) decreased in relation to the tree age, so that in the 8-year-old tree it was about two times of that in the 66-year-old tree. These results suggest that 1) the enhanced efficiency of "shade" shoots is caused by morphologic adaptation, i.e. the more sparsely packed photosynthetic apparatus in needles and shoots, and 2) adaptational possibilities of Norway spruce photosynthetic apparatus, its ecological plasticity diminish during tree ontogenesis.