Photobiological Interactions of Blue Light and Photosynthetic Photon Flux: Effects of Monochromatic and Broad-Spectrum Light Sources

• Published in: Photochemistry and photobiology 2014-05, Vol.90 (3), p.574-584
• Main Authors: Cope, Kevin R., Snowden, M. Chase, Bugbee, Bruce
• Format: Article
• Language: English
• Subjects: Environmental conditions; Light; Morphogenesis; Photoperiod; Photosynthesis; Plant growth; Plant Leaves - growth & development; Vegetables - growth & development
• ISSN: 0031-8655; 1751-1097
• DOI: 10.1111/php.12233

Photosynthesis (Pn) and photomorphogenesis (Pm) are affected by light quality, light intensity and photoperiod. Although blue light (BL) is necessary for normal development, it is less efficient in driving Pn than other wavelengths of photosynthetically active radiation. The effects of BL on Pm are highly species dependent. Here we report the interacting effects of BL and photosynthetic photon flux (PPF) on growth and development of lettuce, radish and pepper. We used light‐emitting diode (LED) arrays to provide BL fractions from 11% to 28% under broad‐spectrum white LEDs, and from 0.3% to 92% under monochromatic LEDs. All treatments were replicated three times at each of two PPFs (200 and 500 μmol m−2 s−1). Other than light quality, environmental conditions were uniformly maintained across chambers. Regardless of PPF, BL was necessary to prevent shade‐avoidance responses in radish and lettuce. For lettuce and radish, increasing BL reduced stem length, and for both species, there were significant interactions of BL with PPF for leaf expansion. Increasing BL reduced petiole length in radish and flower number in pepper. BL minimally affected pepper growth and other developmental parameters. Pepper seedlings were more photobiologically sensitive than older plants. Surprisingly, there were few interactions between monochromatic and broad‐spectrum light sources. Blue light (BL) has profound effects on leaf expansion and stem elongation but the interactions of BL with other wavelengths of photosynthetically active radiation and with total PPF are poorly characterized. We used three broad‐spectrum and four monochromatic LED arrays at two photosynthetic photon flux (PPF) to quantify BL effects on plant growth and development. Regardless of PPF, BL was necessary to prevent shade‐avoidance responses in lettuce and radish but not pepper. Leaf expansion was altered by a unique interaction of BL with PPF. Surprisingly, there were few additional interactions of BL between monochromatic and broad‐spectrum light sources.