EFFECT OF CARBON-DIOXIDE CONCENTRATION ON BIOMASS PRODUCTION AND PARTITIONING IN BETULA-PUBESCENS EHRH SEEDLINGS AT DIFFERENT OZONE AND TEMPERATURE REGIMES

Seedlings of Betula pubescens were grown at two CO2 concentrations, in combination with either two O3 concentrations or two air temperatures, during 34-35 days at 24 h day-1 photoperiod in growth chambers placed in a greenhouse. Increasing the CO2 concentration from 350 to 560 mumol mol-1 at 17-degrees-C air temperature increased the dry weight of the main leaves, main stem, branches and root. The mean relative growth rate (RGR) was increased 10% by CO2 enrichment, while increasing the O3 concentration from 7 to 62 nmol mol-1 decreased the RGR by 9%. The relative biomass distribution between the different plant components was not significantly affected by the CO2 concentration irrespective of the O3 concentration. No significant interactions between CO2 and O3 concentration were found except on leaf size, which was stimulated more by elevated CO2 concentration at high, compared to low, O3 levels. In another experiment, elevated CO2 (700 mumol mol-1) significantly increased the dry weight of the different plant components, and more at 20-degrees-C than at 15-degrees-C. Raising the CO2 concentration increased the RGR by 5 and 10% at 15 and 20-degrees-C, respectively. CO2 enrichment increased the branch dry weight relatively more than the dry weight of the other plant parts. Increasing the CO2 concentration or temperature increased the plant height and stem diameter, however, no interactions between CO2 and temperature were found.