Optimal control of environmental conditions affecting lettuce plant growth in a controlled environment with artificial lighting: A review

Abstract

Lettuce is one of the most popular leafy vegetables produced in controlled environments with artificial lighting (CEALs). Optimal control of environmental conditions can be used to facilitate the improvement of lettuce plant growth and light use efficiency. This article reviews and discusses the effects of light, air velocity, temperature, relative air humidity, and CO2 concentration on the growth and development of lettuce plants in a CEAL. A review of previous studies revealed that light intensity in the range between 200–250 µmol m−2 s−1 with a photoperiod of 16–18 h using red and blue LEDs, with a ratio between 5 and20% for the blue light are optimal to improve lettuce plant growth and light use efficiency. The optimal light quality can also be achieved by using supplemental white or green LEDs, far-red light, and UV-A radiation. Air velocity in the range between 0.3 and 0.7 m s−1 enhances the photosynthetic rate, transpiration rate, and gas diffusion through the boundary layer of the leaf and prevents the occurrence of tipburn. The air temperature of 22–25 °C during the light periods was reported as optimal to enhance CO2 uptake and consequently improve lettuce growth. Relative air humidity in the range between 70 and 80% promotes vegetative growth and reduces water stress by causing the stomata to close. High CO2 concentrations increased photosynthetic rate but also decreased CO2 utilization efficiency. Therefore, CO2 concentration in the range between 1000 and 1500 µmol mol−1 is optimal for high growth rate, productivity, and CO2 utilization efficiency. Most of the previous studies have focused on the effect of light intensity, quality, and duration on the growth and development of lettuce plants under artificial light, with limited information about the interactions of all environmental conditions. This review will be useful for growers, researchers, and designers in the field of plant production in CEALs.