[Effects of CO2 concentration on growth and development of lettuce in controlled environment]

Objective. To study the tolerance of lettuce to elevated CO2 concentration in Controlled Ecological Life Support System (CELSS). Method. Lettuce was cultivated in the Ground-based Experimental Facility for Higher Plant Cultivation in Space (GEFHPCS), in which many parameters were kept unchanged, while concentration of CO2 was controlled at 5 different levels (2000-10000 micromoles mol-1). During the growing periods, the morphologies of lettuce were observed every day, the replenished amounts of CO2 to GEFHPCS and water to the nutrient fluid box as well as the amounts of condensed water collected from GEFHPCS were all recorded every day. After harvest, the output and photosynthetic rate were calculated and lots of constituents of lettuce were analyzed. Result. The growth of lettuce were relatively ideal when CO2 concentration was at 6000 micromoles mol-1, but an obviously withering appearance was found when CO2 concentration increased 10000 micromoles mol-1, this time the output and quality of lettuce were unsatisfactory. Conclusion. It would be optimal when CO2 concentration is controlled at about 6000 micromoles mol-1 in a lettuce-cultivating chamber.