Effects of a new-type inner-canopy illuminant and light quality on spring wheat growth in CELSS

Abstract

Traditional plant illumination in Controlled Ecological Life Support System (CELSS) has been generally roof illumination (RI). In order to improve the utilization efficiency of light energy for cultivating plants, a new-type inner-canopy illuminant (ICI), which was embedded among the stems and leaves of spring wheat, was applied in the research. The experimental group was 50% ICI+ 50% RI, while the control group was 100% RI, both of which consumed the same total electric power. For each of the two groups, six different qualities of light were separately used to study the effects of red, blue and green light under simulated CELSS conditions. By comparing the two groups, it was found that the PPFD (Photosynthetic Photon Flux Density) on the leaf surface was increased in the experimental group, resulting in a shortened growth period, higher net photosynthetic rate (Pn), lower plant height, larger leaf area index (LAI), higher biomass and seed yield. The increased percent of PPFD across the leaf surface under the experimental group on average reached 8.6%–14.6% within 30 days, while PPFD increased by 3.9%–8.0% in 70 days after sowing. An increased seed yield as large as 19.6% per day was achieved in the experimental group. In addition, Red, blue and green light contributed differently to photosynthetic efficiency. Firstly, red light promoted the shortening of growth period, while blue and green light had no significant effect on it. For example, reducing 20% red light caused a 12- or 13-day prolongation of the growth period. Secondly, increasing the ratio of red/blue could increase Pn, plant height, leaf area index, total biomass and seed yield. Thirdly, it can be seen that the green light did not contribute to photosynthesis directly, but it still had an important role in spring wheat growth. Green light significantly increased the tiller number and LAI, as well as total biomass and seed yield, but daily seed yield was not increased under 10% or more green light. The total seed yield was the highest in combination of 80% red +10% blue +10% green light, but the highest daily seed yield was achieved under 90% red +10% blue light for a shorter growth period. The above results should provide a useful reference for choosing the suitable plant lighting method in CELSS.