2017 ASHS Annual Conference

Light is absorbed, transmitted, or reflected by plants at varying efficiencies and responses in relation the light quality of the irradiance. Because of the role of light quality on photosynthesis and the phenlypropanoid pathways for secondary metabolites such as flavonoids, our objectives were to quantify the effect of supplemental light source and spectra on growth, gas exchange, and aroma and flavor of culinary herbs. Sweet basil (Ocimum basilicum L.), dill (Anethum graveolens L.), and flat-leaf parsley (Petroselinum crispum (Mill.) Fuss.) were transplanted into hydroponic systems in a glass-glazed greenhouse. Plants were provided with a supplemental photosynthetic photon flux density (PPFD) of 100 μmol∙m^–2∙s^–1 from a 400-W high-pressure sodium (HPS) lamp or light emitting diodes (LEDs) with red:blue ratios of 93:7 (low blue – LB) or 70:30 (high blue – HB). Gas exchange was measured using an infrared gas analyzer, and chlorophyll fluorescence at morning, midday, and evening was measured using a fluorometer. Accumulation of essential oils for aromas were analyzed with head space gas chromatography (GC) and phenolic flavonols by high performance liquid chromatography (HPLC). Both LED treatments increased photosynthesis for basil (P < 0.001) and parsley (P < 0.001) compared to plants grown under HPS lamps. Stomatal conductance was higher for LB and HB in basil (P < 0.001) compared to HPS, but only HB-treated parsley was higher than HPS lighting (P = 0.020). Both LED treatments increased light-induced stress in plants compared to HPS. Fluorescence for LED treatments in the evening resulted in lower Fv/Fm as versus HPS (P < 0.001). Plants grown under HB lighting were shorter than HPS for basil (P = 0.039) and parsley (P = 0.002). Comparatively, parsley fresh mass (SFM) was lower for HB-treated plants compared to HPS (P = 0.043), while dill SFM was unaffected by supplemental light source. Essential oil and phenolic accumulation was dependent on supplemental light treatment and varied among species. Lighting from LEDs resulted in a two-fold increase in orientin (P = 0.013) and myristicin (P = 0.041) for basil and dill, respectively, while HB increased dillapiole concentration by as much as 89% and over HPS (P = 0.038) for dill. Increased content of aromatic and flavor compounds demonstrate the potential of supplemental lighting systems using specific wavelengths to add value, but come with the caveat of understanding the additional stress imparted onto the photosynthetic mechanisms and the resulting effect on biomass accumulation.