EFFECTS OF CARBON-DIOXIDE CONCENTRATION ON ASSIMILATE PARTITIONING, PHOTOSYNTHESIS AND TRANSPIRATION OF BETULA-PENDULA ROTH AND PICEA-ABIES(L) KARST SEEDLINGS AT 2 TEMPERATURES

Seedlings of Betula pendula Roth. and Picea abies (L.) Karat. were gro wn at 350 and 700 mu mol mol(-1) CO2 for 35 or 45 days at 15 and 20 de grees C in eight growth chambers. The mean photosynthetic flux was 15- 22 mol m(-2) day(-1). The mean relative growth rate was increased by 7 % in Betula and by 10% in Picea at the highest CO2 concentration. This corresponded to an increase in the total plant dry weight of 20 and 1 9%, respectively The shoot:root and leaf:stem ratios were unaffected b y the CO2 concentration in both species. High CO2 levels increased the stem diameter and the number of lateral shoots in Betula. Increasing the temperature did not affect the assimilate partitioning between lea f stem and root in Betula, but the needle:stem ratio decreased in Pice a. Elevated CO2 concentration increased the number of lateral shoots i n Betula more at 15 than at 20 degrees C, however, the total weight of the lateral shoots was not affected. With this exception the effect o f CO2 was generally the same at both temperatures. Measurements of the CO2 exchange rates indicated that a slight acclimation to high CO2 ha d taken place at the end of the experimental period in the two species . Elevated CO2 slightly decreased the transpiration rate of Betula.