• Acclimation;
  • adaptation;
  • climate;
  • gas exchange;
  • Scots Pine;
  • stomatal conductance

1. The geographical aspects in photosynthetic light response and stomatal conductance in the shoots of Pinus sylvestris were studied together with structural properties of shoots and needles. Seven stands within the natural distribution area of P. sylvestris in Europe were chosen. CO2 exchange, irradiance and stomatal conductance (gs) for water vapour were measured and the maximum photosynthetic rate (Pm) was determined from the CO2 exchange measurements.

2. There was a clear pattern in the average values of Pm along the latitudinal gradient. Highest values of Pm were found in the middle parts of the distribution area and they decreased towards both ends of the transect. The highest value was almost twice as high as the lowest one.

3. The between-site variation explained 70% of the total variation in the maximum photosynthetic rate. Pm was not clearly correlated with any single climatic variable or nitrogen concentration in the needles.

4.Pm was closely coupled with stomatal conductance (r2=0·74). The differences in Pm and gs between the sites is likely to reflect adaptation and acclimation to different climates.