EFFECTS OF ATMOSPHERIC CO2 ENRICHMENT ON EARLY GROWTH OF VIVIA-FABA, A PLANT WITH LARGE COTYLEDONS

Seedlings of Vicia faba L. were grown in open-top growth chambers at present (P=350 mumol-1) and at elevated (E=700 mumol mol-1) atmospheric CO2 concentration. The effects Of CO2 enrichment on the first phase of growth after germination were examined over 45d. There were no positive effects Of CO2 enrichment on growth of the seedlings during this early phase. No differences were observed in leaf area or in total dry weight. No differences were found in morphology or anatomy of the leaves. The numbers of stomatal and epidermal cells, thickness of leaf, of epidermis and of mesophyll cell-layers were unaffected by CO2 enrichment. Also, no differences were observed in leaf concentrations of chlorophyll, reducing carbohydrates or starch. These results contrast markedly with results from similar experiments on poplar hybrids and Phaseolus vulgaris obtained in the same growth facility. It seems that the intitial growth is under internal control such that the atmospheric CO2 concentration has no effects. The lack of response in this case may be attributed to the presence and longevity of the large cotyledons which provided available substrate for growth.