Study on the Growing Characteristics of Lettuce Cultivated at Elevated CO_2 Concentrations in Controlled Environment

Abstract：Objective To investigate growing characteristics of plants grown at elevated CO_2 concentrations in controlled environment and provide base for determination of biological components in future space controlled ecological life support system (CELSS). Methods Lettuce (Lactuca sativa var. Youmaicai) was cultivated at higher atmospheric CO_2 concentration gradient (0.05%～2.0% ). Its growing status, physiological character istics and the content of nutrients were evaluated. Results There were some active effects of elevated CO_2 (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 CO_2( 1.5% and 2. 0% ) weakened these effects, and even had some negative impacts. Lettuce could grow normally at elevated CO_2 (0. 1% to 2. 0% ), average shoot height and leaf area of lettuce plants treated at 0. 1% ~2. 0% CO_2 all increased, but the numbers of leaves eliminated gradually. The contents of nitrogen,potassium and Vc in plants decreased, phosphorus content rose and microelement contents had no obvious change in various CO_2 treatments. Conclusion The lettuce can grow nearly normally at higher atmospheric CO_2 concentration without serious growing inhibition or death, which indicated that the Youmaicai held stronger ability of tolerating higher concentration of CO_2, so it's suitable to be determined as a candidate biological component in CELSS.