Growth of lettuce plants (Lactuca sativa L.) under variable-value control of air temperature by using natural light intensity as feedback signal

Lettuce plants (Lactuca sativa L.) were grown under different regimes of variable-value control of air temperature, where the set values of air temperature increased quadratically with the natural light intensity in the different dynamic ranges. Under the regime of lower night temperature and larger dynamic range of air temperature, succulent growth was prevented, and leaf fresh and dry weights per unit leaf area became larger because of leaf thickening with well developed spongy layer. The results suggest that the variable value control of air temperature by using the natural light intensity as a feedback signal can improve plant growth under controlled environment.