The role of light quality of photoperiodic lighting on photosynthesis, flowering and metabolic profiling in Ranunculus asiaticus L.

ABSTRACT

Photoperiodic light quality affects flowering of long day plants, by influencing the phytochrome photoequilibria (PPE) at plant level; however, the most effective light spectrum to promote flowering is still unknown for most of the flower crops. We evaluated the influence of light spectrum of three light sources, with different induced PPE, on photosynthesis, metabolic profiling, plant growth and flowering in two hybrids of Ranunculus asiaticus L., MBO (early flowering) and MDR (medium earliness). Three photoperiodic treatments were compared to natural day length (NL) white fluorescent light (PPE 0.84), light emitting diodes (LEDs) with redfar red (RFR) light at 31 ratio (PPE, 0.84) and LEDs with RFR light at 13 ratio (PPE 0.63). Under natural light, net photosynthesis was higher in MDR than in MBO, while photochemistry was similar in the hybrids. Compared to NL, photoperiodic treatments did not affect net photosynthesis, while they promoted the quantum yield of PSII and reduced the non-photochemical quenching. Under NL, plant growth was greater in MBO, while flowering started earlier in MDR and flowers characteristics were similar in the hybrids. Despite the greater sensitivity of MDR plants in terms of metabolism, photoperiodic lighting improved plant growth and reduced the flowering time only in MBO, with a stronger effect under RFR 31 light. MDR plants were characterized by higher soluble sugars, polyphenols, photosynthetic pigments and proteins, while MBO plants by higher starch and amino acid content. The morphological effects of photoperiodic light quality and the hybrid-specific response should be taken into account to optimize lighting protocols in commercial farms.