Responses of a long greenhouse tomato crop to summer CO2 enrichment

While CO2 enrichment generally benefits tomato fruit production in winter its effects on summer tomato production (under high air temperature and strong ventilation) are still not clear, especially when the crop has been subjected to long-term CO2 enrichment in winter. Therefore, a study was initiated in 2005 to determine the feasibility of summer CO2 enrichment in southwestern Ontario, a major greenhouse vegetable production area in North America with very hot summers. The long tomato crop (cv. Rapsodie) was planted into rockwool slabs in six greenhouse compartments in January. From January to the middle of June, the tomato plants in all six greenhouse compartments were subjected to the same standard CO2 enrichment practice. From the end of June to August, three CO2 treatments (two compartments for each treatment) were applied: Control (ambient/no enrichment), Enrich1 (800 µL L-1 when ventilation was less than 10% and 400 µL L-1 when less than 50%) and Enrich2 (1200 µL L-1 when ventilation was less than 10% and 500 µL L-1 when less than 50%). In all treatments, CO2 enrichment ceased when ventilation requirement was more than 50%. Leaf photosynthesis, as indicated by the CO2 response curve, partially acclimated to the CO2 enrichment. Marketable fruit yield was reduced by the summer CO2 enrichment. Leaf deformation [short, thick, curled and somewhat crisp, dark grey-green leaves, so-called short leaf syndrome (SLS)] was observed in the greenhouse compartments with summer CO2 enrichment. SLS developed under high light intensity and high CO2 concentration might have limited response of the tomato crop to summer CO2 enrichment. Further investigation on the cause and mechanism of SLS is needed to improve the response of greenhouse tomatoes to summer CO2 enrichment. Key words: Photosynthesis, Lycopersicon esculentum, high temperature stress, acclimation