GAS-EXCHANGE IN YOUNG SCOTS PINE FOLLOWING PRUNING OF CURRENT SHOOTS

A pine shoot beetle attack was simulated by cutting all current shoots in the upper crown of 2 20-yr-old Scots pines (Pinus sylvestris L) while gas exchange was followed continuously before and after the shoot removal. Net photosynthetic rate and mesophyll conductance of the 2-yr-old shoots decreased by almost-equal-to 50% immediately after pruning but recovered within 10 d after the shoot removal. The quantum yield was also much lower after cutting. Water status and transpiration rate were not systematically affected by the treatment. Possible explanations of the photosynthetic decrease could be an accumulation of assimilation products decreasing the mesophyll conductance of carbon dioxide to the chloroplasts or changes of the carbon allocation pattern.