A BRANCH BAG TECHNIQUE FOR SIMULTANEOUS CO2 ENRICHMENT AND ASSIMILATION MEASUREMENTS ON BEECH (FAGUS-SYLVATICA L)

A cheap CO2 enrichment system was designed to perform continuous gas exchange measurements of branches of mature European beech trees (Fagus sylvatica L.). Branches were grown at ambient (350 cm(3) m(-3)) and elevated CO2 (700 cm(3) m(-3)) during the whole 1992 leafy period. Leaks resulting from airtightness defaults in the system appeared to be low enough to measure accurately net CO2 assimilation and transpiration rates during the day. However, the CO2 exchange rates during the night (respiration) were too low to allow accurate measurements. Elevated CO2 had a great effect on the net assimilation rate of branches via its influence on both the C-3 photosynthetic pathway and the shade-tolerance of beech frees (85% increase). The A/C-a curves showed no acclimation effect to high CO2, both control and enriched branches increasing their net assimilation in the same way. The decrease of net assimilation rates in mature leaves was similar for both control and enriched branches. The pattern of daily transpiration rates remained the same for both control and enriched branches, hence we can assume that there was no visible CO2 effect on stomata.