Influence De L’enrichissement Carboné Et De Son Mode De Distribution Sur L’évolution Des Échanges Gazeux De La Tomate De Serre

Net photosynthesis, stomatal conductance, internal CO 2 concentration and transpiration were measured on the fifth well-developed and excised leaf of tomato seedlings (Lycopersicon esculentum Mill. ’Vedettos’) 48–83 d old. These measurements were taken in order to monitor the evolution of the gas exchanges of seedlings exposed to concentrations of 330 or 1000 ppm, continuously, to 1000 ppm from 06: 00 h to 10: 00 h or to 1000 and 330 ppm alternately every 2 h. CO 2 enrichment substantially increased the net photosynthesis rate of the seedlings, particularly at the beginning of the experiment. The long-term effects of CO 2 enrichment subsided after a few weeks of treatment. Intermittent CO 2 enrichment is partially helpful in remedying the loss of effectiveness of the CO 2 after a long period of enrichment. High CO 2 concentrations reduced the opening of the stomata. Our work shows that maintaining a high internal CO 2 content in the leaves would indirectly reduce the stomatal conductance of the seedlings. However, our results show that the long-term loss of photosynthetic efficiency in the enriched seedlings cannot be attributed solely to an increase in the resistance of the stomata, since the internal CO 2 concentration of the leaves remains very high regardless of which method of CO 2 enrichment is used. Continuous CO 2 enrichment improved the water uptake efficiency of the seedlings.