A Controlled Ecological Life Support System (CELSS) is considered to be the fundamental solution for long-term manned space exploration. It uses plants to provide astronauts with food and O2 to achieve self-sufficiency inside the system. Due to lack of energy in space, it is a significant issue to increase the energy-using efficiency of plant cultivation [1], [2], [3], [4], [5] and [6].
Environmental control is of great importance to the production efficiency of plants, including lighting, temperature and pressure [7] and [8]. Illuminant is the main source of energy consumption, so optimizing the lighting conditions is an important way to elevate the energy-using efficiency. Photoperiod is a key index, which is of significance for plant growth. Opinions upon the effects of photoperiod on wheat are divided. Some reported that wheat got higher yield at longer photoperiod, but more reports indicated that shorter photoperiod increased the number and weight of seeds. The growth process is significantly impacted by the photoperiod. The duration of jointing stage was reported to be shortened by longer photoperiod [9]. Miralles reported that constant longer photoperiod reduced the duration from sowing to double ridge [10]. However, research upon the effect of photoperiod in CELSS environment has been rarely reported.
In addition, effects of photoperiod on different stages of wheat growth have been seldom researched. The role of photoperiod is different in different growth stages, so the optimal photoperiod may be different for different stages. For example, the best photoperiod before flowering may be unsuitable for the stage after flowering.
Therefore, effects of photoperiod on wheat growth in different stages were explored in this research, in order to provide theoretical support for the optimization of lighting strategy in CELSS.