INFLUENCE DE L’ENRICHISSEMENT CARBONÉ ET DE SON MODE DE DISTRIBUTION SUR L’ÉVOLUTION DES ÉCHANGES GAZEUX DE LA TOMATE DE SERRE

Abstract

Net photosynthesis, stomatal conductance, internal CO2 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. CO2 enrichment substantially increased the net photosynthesis rate of the seedlings, particularly at the beginning of the experiment. The long-term effects of CO2 enrichment subsided after a few weeks of treatment. Intermittent CO2 enrichment is partially helpful in remedying the loss of effectiveness of the CO2 after a long period of enrichment. High CO2 concentrations reduced the opening of the stomata. Our work shows that maintaining a high internal CO2 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 CO2 concentration of the leaves remains very high regardless of which method of CO2 enrichment is used. Continuous CO2 enrichment improved the water uptake efficiency of the seedlings.Key words: Carbon dioxide, intermittent enrichment, gas exchanges, tomato, greenhouse, Lycopersicon esculentum Mill.