High Light Intensity from Blue-Red LEDs Enhance Photosynthetic Performance, Plant Growth, and Optical Properties of Red Lettuce in Controlled Environment

Plant factories using artificial light to produce vegetables have high energy costs due to the high demand for electricity for lighting. Compared to conventional light sources, light-emitting diodes (LEDs) offer the possibility of tailoring the light spectrum and regulating light intensity and are more energy-efficient in terms of energy conversion regardless of the levels of lighting intensity. Optimal light intensity and daily light integral (DLI) requirements are key factors for plant growth; however, their values vary among species and varieties. Our experiment aimed to identify the best light intensity to produce lettuce plants in controlled environment. Lettuce plants of the type Batavia cv ‘Blackhawk’ were grown in plastic pots filled with perlite and peat (20:80 v/v) for 33 days in a growth chamber under blue (B, 20%) and red (R, 80%) LED light at a photosynthetic flux density of 130 µmol m −2 s −1 (BR 130, DLI 7.49 mol m −2 d −1 ), 259 µmol m −2 s −1 (BR 259, DLI 14.92 mol m −2 d −1 ), and 389 µmol m −2 s −1 (BR 389, DLI 22.41 mol m −2 d −1 ). Our results showed that increasing light intensity and DLI promotes net photosynthesis, sustains the electron transport rate (ETR), and stimulates the synthesis of anthocyanins and carotenoids, with positive results for plant photoprotection. Furthermore, the decreases in vegetation indexes (photochemical reflectance index (PRI), greenness, and modified chlorophyll absorption in reflectance index (MCARI1)) also indicate changes in photosynthetic pigment content in response to plant acclimation to different DLIs. Among the three light intensities, 389 µmol m −2 s −1 (DLI 22.41 mol m −2 d −1 ) gave the best results for growing Batavia red lettuce cv ‘Blackhawk’, since it enhances both production and qualitative traits. These results highlight the importance of a proper light intensity to promote plant growth and qualitative traits and to reach high production targets. Hence, preliminary screening of plant performance under different light treatments is recommended to optimise plant response to artificial lighting

Modulation of light spectrum for controlling plant growth and development of flower species for greenhouse cultivation and leafy vegetables for indoor cultivation

Light represents a key factor for plant development because it drives photosynthesis, growth and morphogenesis. Optimizing plant growth by modulating the light spectrum is an attractive perspective to obtain specific morphological and physiological traits in different plant species. The aim of this PhD thesis was to investigate the physiological and morphological effects of light modulation on ornamental and vegetable species, and to contribute to the development of new lighting protocols for plant cultivation. The ornamental species chosen for these studies, was Rannunculus asiaticus L. a quantitative long day geophyte original from the Mediterranean basin and Asia Minor, cultivated for cut stems and potted plant production. In a preliminary experiment, the photosynthetic process was characterized in R. asiaticus plants to reduce the gap of information on the physiology of this species. Plants were grown in pots under controlled environmental conditions at the Photosynthetic Photon Flux Density, PPFD of 200 µmol m-2 s-1, provided by fluorescent white light lamps. We compared two R. asiaticus hybrids, MDR and MBO, and two tuberous root preparation procedures (rehydration (C), rehydration plus vernalization (V)). The results indicated an intrinsic difference between the two hybrids and a hybrid-specific response to the tuberous root preparation procedures in terms of photosynthetic capacity and plant growth. Moreover, the vernalization treatment promoted starch degradation and increased sucrose and amino acids content in the tuberous roots. These findings were confirmed in a second experiment carried out in a cold greenhouse on the same hybrids under different photoperiodic lighting treatments. The treatments consisted in a day extension, by means of fluorescent light or Red and Far Red Light Emitting Diodes (LEDs) at a ratio of 3:1 and 1:3 compared to a typical natural daylength (NL, short day) in the period December - March. Compared to the NL treatment, photoperiodic lighting promoted photochemical processes, reducing the thermal dissipation and the time to complete flowering in both MBO and MDR hybrids; furthermore, in MBO anticipated the formation of flower buds. Photoperiodic lighting also modified the metabolic profile in both hybrids, inducing in MDR hybrid higher soluble sugars, polyphenols, proteins and pigment content, while in MBO higher amino acids and starch content. The R:FR 3:1 treatment promoted the photosynthetic pigments in both hybrids. The experiments on leafy vegetables were carried out to assess 1) the influence of different blue (B): red (R) ratios (25:75; 20:80 and 10:90 ratios) and 2) the effect of increasing far red (FR) intensity (0, 25, 50, 75 µmol μmol m−2 s−1) over a fixed 20:80 ratio BR spectrum on plant growth, photosynthesis and leaf phenolic compounds in Chicorium endivia L. ‘Lindo’ and Lactuca sativa L. ‘Blackhawk’. The results showed that a precise balance between B and R light is needed to promote photosynthetic activity and plant growth in both species. The addition of different FR light intensities reduced photosynthesis in both species. This decrease was likely linked to ETR drop in lettuce whereas in endive to a reduction of photosynthetic pigment pool. FR light favored the biomass partitioning toward aboveground structures in endive, and both B:R light and FR light affected the polyphenol profile in both species. In conclusion, light modulation can be considered a powerful tool to modulate qualitative attributes in ornamental plants and leafy vegetables. The results of this study might have scientific as well as practical implication. The optimized growth protocol could be applied on large scale greenhouses or indoor cultivation systems to increase the plant yield and functional attributes

Metabolic Profile and Performance Responses of Ranunculus asiaticus L. Hybrids as Affected by Light Quality of Photoperiodic Lighting

R. asiaticus is a quantitative long day plant grown for cut flowers and flowering potted plants production. We evaluated the influence of light spectrum of three light sources for end-of-day photoperiodic treatments, with different phytochrome photoequilibria (PPE) induced at plant level, on metabolic profiling of two hybrids of Ranunculus asiaticus L., MBO and MDR, in plants from vernalized tuberous roots. The following treatments were compared to natural day length (NL): white fluorescent light (FL, PPE 0.84), LEDs Red:Far Red light at 3:1 ratio (R:FR 3:1, PPE, 0.84), and LEDs Red:Far Red light at 1:3 ratio (R:FR 1:3, PPE 0.63). Measurements were carried out to evaluate the time course of carbohydrate, amino acid and protein levels throughout the growing cycle in tuberous roots and leaves, in relation to the different plant stages (pre-planting, vegetative phase and flowering). The study of metabolic profiling suggested that the differences between the tuberous root reserves of the two R. asiaticus hybrids could be responsible for the capacity of MBO to exert an early flowering. In particular, the proton-consuming synthesis during pre-planting of two amino acids, alanine and aminobutyric acid (GABA), is able to buffer the cytoplasmic acidosis and pH altered by the vernalization process, and GABA istself can efficiently scavenge reactive oxygen species. This fast response to the stress caused by vernalization allows MBO plants to accelerate the process of vegetative development and flowering. Some other changes in metabolites profile were certainly related to the different response to day length and photoperiodic light quality in the two hybrids, like dose exerted by low R:FR lighting in both MBO and MDR. However, the most of responses are under a strict genetic control

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

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 the flower crops. We evaluated the influence of light spectrum of three light sources, with different induced PPE, on photosynthesis, metabolic profiling and plant growth and flowering in two hybrids of Ranunculus asiaticus L., MBO and MDR. Three photoperiodic treatments were compared to natural day length (NL): white fluorescent light (FL, PPE 0.84), LEDs Red:Far Red light at 3:1 ratio (R:FR 3:1, PPE, 0.84), and LEDs Red:Far Red light at 1:3 ratio (R:FR 1:3, 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 R:FR 3:1 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. This article is protected by copyright. All rights reserved

Foliar Nutrition Influences Yield, Nut Quality and Kernel Composition in Hazelnut cv Mortarella

In hazelnut, foliar nutrition is utilized globally to integrate microelement deficiencies and optimize their assimilation and effects on yield performances. Nevertheless, nut quality and kernel composition can be positively affected by foliar nutrition. Recently, several studies pointed out the need for increasing the sustainability of orchard nutrition by proposing the management of not only micronutrients, but also main components, such as nitrogen, through foliar spraying. In our study, different foliar fertilizers were used to understand the effectiveness of supporting hazelnut productivity and nut and kernel quality. Water was used as a control. Foliar fertilizations affected tree annual vegetative growth, improved kernel weight and decreased the incidence of blanks compared to the control. Differences in fat, protein, and carbohydrate concentration were also found among treatments, with increased fat concentrations and total polyphenols content in fertilized treatments. Foliar fertilization improved the oil composition of the kernels, though fatty acid composition responded differently to nutrients spray. Oleic acid concentration was promoted, while palmitic acid concentration was reduced in fertilized plants compared to control trees. Furthermore, CD and B trees were characterized by an increase in the ratio of unsaturated/saturated fatty acids compared to untreated trees. Finally, foliar spraying improved lipid stability compared to the control due to higher total polyphenol concentration

Vernalization Procedure of Tuberous Roots Affects Growth, Photosynthesis and Metabolic Profile of Ranunculus asiaticus L.

In Ranunculus asiaticus L., vernalization of propagation material is a common practice for the production scheduling of cut flowers, however little is known about the plant physiology and metabolism of this species as affected by cold treatments. We investigated the influence of two hybrids, MBO and MDR, and three preparation procedures of tuberous roots, only rehydration (control, C), and rehydration plus vernalization at 3.5 °C for 2 weeks (V2) and for 4 weeks (V4), on plant growth and flowering, leaf photosynthesis, and leaf metabolic profile in plants grown in pot in a cold greenhouse. Net photosynthesis (NP) was higher in MDR than in MBO. In the two genotypes, the NP did not change in V2 and increased in V4 compared to C in MBO, while was unaffected by vernalization in MDR. Quantum yield of PSII electron transport (ΦPSII), linear electron transport rate (ETR) and non-photochemical quenching (NPQ) did not differ in the two hybrids, whereas maximal PSII photochemical efficiency (Fv/Fm) was higher in MBO than in MDR. Fluorescence indexes were unaffected by the preparation procedure, except for ETR, which decreased in V2 compared to C and V4 in MDR. A significant interaction between genotype and preparation procedure was found in plant leaf area, which was reduced only in V4 in MBO, while decreased in both the vernalization procedures in MDR. In Control plants, flowering started in 65 days in MBO and 69 days in MDR. Compared to controls, both the vernalization treatments anticipated flowering in MDR, while they were detrimental or only slightly efficient in promoting flowering in MBO. Vernalization always reduced the quality of flower stems in both the hybrids

Light spectral composition affects metabolic response and flowering in non-vernalized Ranunculus asiaticus L

We investigated the influence of photoperiodic light spectrum, inducing different phytochrome photoequilibria (PPE) at plant level, on photosynthesis, metabolic profiling, plant growth and flowering of Ranunculus asiaticus L. hybrids, MBO and MDR with different flowering earliness, grown in glasshouse from rehydrated dry tuberous roots. Plants were exposed to three photoperiodic treatments (day extension to 14 h), compared to natural day length (NL): white fluorescent light (PPE 0.84), and LEDs Red:Far Red light at 3:1 ratio (PPE 0.84) and 1:3 ratio (PPE 0.63). We discuss the results also compared to data on plants from rehydrated and vernalized roots previously reported in Modarelli et al., 2000a. Leaf gas exchanges and quantum yield of PSII electron transport were higher in MDR than in MBO, whereas non-photochemical quenching showed the opposite behaviour. In MDR, R:FR 3:1 light was the most effective in promoting stomatal conductance, while it reduced photochemistry and increased heat dissipation compared to other treatments. Under NL, leaf area was greater in MBO while flowering earliness and flower stems were similar in the hybrids. Photoperiodic treatments did not influence the plant growth while anticipated flowering in both the hybrids. In both the hybrids, lighting did not change the content of chlorophylls, carotenoids, glucose and sucrose. The greater number and expansion of leaves in MBO, except under R:FR 3:1, was accompanied by a lower photosynthetic capacity per leaf area. Conversely, in MDR, with lower leaf number, area and DW, an interesting increase of N-containing metabolites (i.e. chlorophylls and amino acids) occurred, thus exerting a positive effect on photosynthetic rate

Vernalization Procedure of Tuberous Roots Affects Growth, Photosynthesis and Metabolic Profile of Ranunculus asiaticus L

In Ranunculus asiaticus L., vernalization of propagation material is a common practice for the production scheduling of cut flowers, however little is known about the plant physiology and metabolism of this species as affected by cold treatments. We investigated the influence of two hybrids, MBO and MDR, and three preparation procedures of tuberous roots, only rehydration (control, C), and rehydration plus vernalization at 3.5 degrees C for 2 weeks (V2) and for 4 weeks (V4), on plant growth and flowering, leaf photosynthesis, and leaf metabolic profile in plants grown in pot in a cold greenhouse. Net photosynthesis (NP) was higher in MDR than in MBO. In the two genotypes, the NP did not change in V2 and increased in V4 compared to C in MBO, while was unaffected by vernalization in MDR. Quantum yield of PSII electron transport (phi PSII), linear electron transport rate (ETR) and non-photochemical quenching (NPQ) did not differ in the two hybrids, whereas maximal PSII photochemical efficiency (Fv/Fm) was higher in MBO than in MDR. Fluorescence indexes were unaffected by the preparation procedure, except for ETR, which decreased in V2 compared to C and V4 in MDR. A significant interaction between genotype and preparation procedure was found in plant leaf area, which was reduced only in V4 in MBO, while decreased in both the vernalization procedures in MDR. In Control plants, flowering started in 65 days in MBO and 69 days in MDR. Compared to controls, both the vernalization treatments anticipated flowering in MDR, while they were detrimental or only slightly efficient in promoting flowering in MBO. Vernalization always reduced the quality of flower stems in both the hybrids