Qingwu (William) Meng recently delivered an oral presentation at the 2016 American Society for Horticultural Science (ASHS) annual conference in Atlanta, GA. His talk was about how blue, red, and far-red radiation interacted to influence plant growth, morphology, and pigmentation. He won 3rd place in the Controlled Environment Working Group graduate student oral competition.

Watch the entire presentation here:


By Qingwu (William) Meng and Erik Runkle

Horticultural lighting has primarily focused on photosynthetically active radiation, especially blue (B, 400 to 500 nm) and red (R, 600 to 700 nm), and its effects on plant growth. However, far-red (FR, 700 to 800 nm) radiation regulates numerous pathways crucial to photomorphogenesis, thus meriting consideration in sole-source plant lighting applications. We investigated how interactions among B (peak=450 nm), R (peak=660 nm), and FR (peak=730 nm) radiation from light-emitting diodes influenced growth of green butterhead lettuce (Lactuca sativa) ‘Rex’, red oakleaf lettuce ‘Cherokee’, and basil (Ocimum basilicum) ‘Genovese’. Seedlings were grown in a growth chamber at 22 °C and were continuously irradiated by 180 µmol∙m−2∙s−1 of B and/or R radiation at various B-to-R ratios (R180, B30R150, B90R90, and B180, where subscripts indicate respective photon flux densities), with or without 30 µmol∙m−2∙s−1 of FR radiation (FR30). Growth, morphology, and pigmentation were quantified 12 and 16 days after sowing lettuce and basil, respectively. FR30 increased leaf length and shoot weight of all crops, although the effects were more pronounced when FR30 was added to B90R90 than to B30R150. For example, the addition of FR30 increased shoot dry weight of all crops by 34–43% at B90R90, in contrast to 8–17% at B30R150. Adding FR30 increased root dry weight of basil by 18–26% at B30R150 or B90R90 and that of lettuce ‘Cherokee’ by 25% at B30R150, but did not influence that of lettuce ‘Rex’. Adding FR30 to B+R radiation reduced chlorophyll content in lettuce by 10–20%, but not in basil. In the absence of B radiation, R180FR30 produced spindly lettuce seedlings with elongated, curling, chlorotic, and high-moisture leaves. Partially substituting B radiation for R radiation in R180FR30 suppressed hypocotyl and leaf length of lettuce and increased chlorophyll content in both lettuce and basil. A color space analysis revealed that more B radiation or lack of FR radiation corresponded with darker and redder leaves of lettuce ‘Cherokee’, possibly linked to a greater anthocyanin concentration. We conclude that both B and R radiation are required for desirable plant traits, and that B and FR radiation exert antagonistic effects on extension growth and pigmentation. FR radiation can be added to sole-source B+R lighting to increase leaf expansion, radiation capture and thus, growth.

Grow greens with blue, red and far-red LEDs