THE IMPACT OF CO2 ENRICHMENT ON WATER RELATIONS IN MARANTHES-CORYMBOSA AND EUCALYPTUS-TETRODONTA

Seeds of Maranthes corymbosa Blume and Eucalyptus tetrodonta F.Muell w ere sown under ambient or CO2 enriched conditions (two replicate tents per treatment) in tropical Australia and allowed to grow, rooted in t he ground, for 20 months. For both species, periodic measurements of l eaf water potential, stomatal conductance and leaf temperature were ma de on four replicate leaves on each of four replicate trees within eac h tent. Measurements were made in November (M. corymbosa) and June (E. tetrodonta). At the same time, atmospheric wet and dry bulb temperatu res were recorded and hence leaf-to-air vapour presure difference (LAV PD) calculated. Measurements of pre-dawn leaf water potential were als o made on E. tetrodonta. Leaves were also taken to the laboratory, reh ydrated to full turgor and pressure-volume analyses undertaken. For M. corymbosa, leaf water potential was lower throughout the day for cont rol leaves compared to leaves growing in CO2 enriched air. Similarly, pre dawn leaf water potential was lower for control E. tetrodonta tree s than for trees grown with CO2 enrichment. However, mid-morning and m id-afternoon values of leaf water potential for E. tetrodonta were sli ghtly lower for plants growing in CO, enriched air compared to control plants. In both species, stomatal conductance was consistently lower for trees grown in CO2 enriched air than for controls. Whole plant hyd raulic conductivity of both species was significantly lower for trees grown in CO2 enriched air than for control trees. For both species, ma ximum turgor and bulk volumetric elastic modulus increased and osmotic potential at zero turgor decreased for trees grown in CO2 enriched ai r.