Acclimating Cucumber Plants to Blue Supplemental Light Promotes Growth in Full Sunlight

Abstract

Raising young plants is important for modern greenhouse production. Upon transfer from the raising to the production environment, young plants should maximize light use efficiency while minimizing deleterious effects associated with exposure to high light (HL) intensity. The light spectrum may be used to establish desired traits, but how plants acclimated to a given spectrum respond to HL intensity exposure is less well explored. Cucumber (Cucumis sativus) seedlings were grown in a greenhouse in low-intensity sunlight (control; ∼2.7 mol photons m–2 day–1) and were treated with white, red, blue, or green supplemental light (4.3 mol photons m–2 day–1) for 10 days. Photosynthetic capacity was highest in leaves treated with blue light, followed by white, red, and green, and was positively correlated with leaf thickness, nitrogen, and chlorophyll concentration. Acclimation to different spectra did not affect the rate of photosynthetic induction, but leaves grown under blue light showed faster induction and relaxation of non-photochemical quenching (NPQ) under alternating HL and LL intensity. Blue-light-acclimated leaves showed reduced photoinhibition after HL intensity exposure, as indicated by a high maximum quantum yield of photosystem II photochemistry (Fv/Fm). Although plants grown under different supplemental light spectra for 10 days had similar shoot biomass, blue-light-grown plants (B-grown plants) showed a more compact morphology with smaller leaf areas and shorter stems. However, after subsequent, week-long exposure to full sunlight (10.7 mol photons m–2 day–1), B-grown plants showed similar leaf area and 15% higher shoot biomass, compared to plants that had been acclimated to other spectra. The faster growth rate in blue-light-acclimated plants compared to other plants was mainly due to a higher photosynthetic capacity and highly regulated NPQ performance under intermittent high solar light. Acclimation to blue supplemental light can improve light use efficiency and diminish photoinhibition under high solar light exposure, which can benefit plant growth.

LED Lighting: A Grower’s Guide to Light Spectra

“…Although LED lighting offers complete spectral freedom, this comes at the expense of spectral consistency between growers and setups, which can make it difficult to unravel the effects of differing spectral conditions on crop performance. Despite this, there is an overall trend for greater biomass with increasing fractions of red light, whereas higher fractions of blue tend to increase photosynthetic capacity, which is beneficial under higher light intensities (e.g., under sunlight) (Hogewoning et al 2010;Kaiser et al 2019a;Kang et al 2021), pigment content, and secondary metabolite synthesis (Tables 1 and 2). Although these general trends are worth adhering to (and a basic protocol for determining the optimal R:B ratio is provided in Fig.…”

Response of photomorphogenesis and photosynthetic properties of sweet pepper seedlings exposed to mixed red and blue light

“…It is assumed that mixed RL and BL with higher ratio of BL were more inhibitive of hypocotyl and leaf elongation and inducing in the sweet pepper seedlings a more compact morphology with shorter stems and smaller leaf areas than monochromatic BL. These results indicated that increasing BL could inhibit cell division and expansion ( Kang et al., 2021 ). Furthermore, lower levels of GA and IAA under a low RL/BL ratio of 1R3B may lead to reduced elongation of pepper seedlings’ shoots ( Islam et al., 2014 ; Matsuo et al., 2019 ).…”

“…Hence, RL significantly reduced P n and F v / F m , which might result in acceleration of leaf senescence ( Su et al., 2014 ). The photodamaged PSII induced by RL could be alleviated by BL, which could benefit pepper seedling growth by improving light use efficiency and diminish photoinhibition ( Miao et al., 2019 ; Kang et al., 2021 ). On the other hand, the P n and F v / F m , Φ PSII , ETR and qP of seedlings exposed to 3R1B treatment was found to be significantly higher than those of other light spectra.…”

“…Apparently, the increased concentration of light absorbing pigments in leaves has considerable consequences for leaf CO 2 uptake under this treatment. This may be also related to the well-developed stomata ( Li et al., 2020 ; Kang et al., 2021 ), higher stomatal conductance ( Hamedalla et al., 2022 ) and high nitrogen accumulation in leaves under this spectral wavelength ( Fan et al., 2022 ). Consequently, the morphology of pepper seedlings under this light spectrum revealed higher SLA, FW and DW of shoots and roots, and thus better performance compared to other treatments.…”

Magic Blue Light: A Versatile Mediator of Plant Elongation

“…In cucumbers, supplemental blue LEDs at 15 µmol m −2 s −1 with high-pressure sodium (HPS) lamps (90 µmol m −2 s −1 ) for 18 h d −1 not only decreased hypocotyls’ elongation, but also increased the leaf area, increased the fresh and dry weight, and enhanced their development, compared with HPS only [ 140 ]. In the same species grown in a greenhouse under low-intensity sunlight (about 2.7 mol m −2 d −1 ), 10 days of SL with blue LEDs relative to white, red, or green LEDs (at 120 µmol m −2 s −1 for 10 h d −1 ; 4.3 mol m −2 d −1 ) caused more compact plants with shorter stems and smaller leaf areas, despite similar shoot biomass [ 141 ]. Furthermore, after transferring to full sunlight (10.7 mol m −2 d −1 ), plants from the blue LED treatment developed similar leaf areas and 15% higher shoot biomass, showing better acclimation ability compared to other spectral treatments [ 141 ].…”