Study on the Growing Characteristics of Lettuce (var. Youmaicai) Cultivated at Elevated CO ₂ Concentrations in Controlled Environment

Lettuce (Lactuca sativa var. Youmaicai) was cultivated at higher atmospheric CO₂ concentration gradients (0.05∼2.0%), and then some parameters such as comprehensive evaluation of plant growing states, rates of photosynthesis and transpiration were carried out. There were some positive effects of elevated CO₂ (0.1% to 1.0%) on the average rates of photosynthesis and transpiration of the collective lettuce leaves and the contents of chlorophyll and carotenoid, but excessive CO₂ (1.5% and 2.0%) weakened the effects, and even had some negative impacts; average shoot height and leaf area of lettuce plants treated at 0.1%∼2.0% CO₂ all increased, but the numbers of leaves reduced; The contents of nitrogen, potassium and vitamin C in plants decreased, but phosphorus content rose and microelement contents had no obvious change in various CO₂ treatments. The lettuce can grow nearly normally at higher atmospheric CO₂ concentration without serious growing inhibition or death, which indicated that the Youmaicai held strong ability of tolerating higher concentration of CO₂, so it's suitable to be determined as a candidate biological component in controlled ecological life support system (CELSS).