Fixed versus altered-spectrum lighting effect on the vegetative and flowering characteristics of <i>Zinnia elegans</i> L.

In an experiment, zinnia plants were grown under fixed or altered-light qualities during their vegetative (phase I) and flowering phase (phase II) using red (R), blue (B) and RB (3:1) light emitting diodes (LEDs). In the altered treatments, the plants were shifted to a chamber illuminated with a different light quality than what they experienced during their vegetative phase. The results showed that plants grown under altered-light R-RB were superior in terms of their vegetative and flowering properties, such as plant height, leaf and root biomass and early flowering, compared to the plants treated with fixed light. Interestingly, plants illuminated with RB light during the vegetative phase were shorter than those illuminated with R or B light. This unexpected result was not attributed to shade avoidance syndrome, which is common in some species, but to a possible ‘full-spectrum deficiency’ that affects the growth behaviour of plants under R or B light, causing them to search for the missing part of the light spectrum. The results of this experiment shed light on the possible effects of different light qualities on the growth behaviour of plants and show how important it is to consider the adapted spectrum for optimal growth and development.