Amount Of Light Research Articles

Photo-selective nets (PSNs) affect predation by Harmonia axyridis on Myzus persicae

Photo-selective nets (PSNs) can increase agricultural crop production by modifying the quantity and quality of light that reaches the plants. PSNs also have the potential to affect arthropod pest populations and their natural enemies. The present study aimed to assess the impact of PSN systems on coccinellid predation. Experiments were carried out in microcosm conditions to evaluate the efficiency (prey localization and predation) of the multicolored Asian lady beetle, Harmonia axyridis (Pallas), when preying on the green peach aphid, Myzus persicae (Sulzer), on potato plants. Three colors of nets were tested and compared to control (no net): black SN (standard net), pearl PSN, and red PSN, using H. axyridis third-instar larvae (L3), females and males. We hypothesized that pearl and red PSN and black SN would alter the predator behavior, delaying the time to aphid colony localization, or by reducing overall aphid predation. Our results showed that aphid colonies were not affected by any PSN or the black SN in the absence of predators. Aphid colony localization by adult coccinellids was delayed under black SN, and favored under pearl PSN, but overall aphid predation was unaffected by net type. There were no significant differences among treatments in interplant movement of L3, females, or males. We conclude that, under laboratory conditions, pearl PSN, red PSN, and black SN can affect aphid colony localization by H. axyridis, but do not affect predation efficiency. Subsequent trials in the field would be required to further clarify the effects of PSNs on H. axyridis foraging behavior.

Underwater light climate and wavelength dependence of microalgae photosynthetic parameters in a temperate sea.

Studying how natural phytoplankton adjust their photosynthetic properties to the quantity and quality of underwater light (i.e. light climate) is essential to understand primary production. A wavelength-dependent photoacclimation strategy was assessed using a multi-color pulse-amplitude-modulation chlorophyll fluorometer for phytoplankton samples collected in the spring at 19 locations across the English Channel. The functional absorption cross section of photosystem II, photosynthetic electron transport (PETλ) parameters and non-photochemical quenching were analyzed using an original approach with a sequence of three statistical analyses. Linear mixed-effects models using wavelength as a longitudinal variable were first applied to distinguish the fixed effect of the population from the random effect of individuals. Population and individual trends of wavelength-dependent PETλ parameters were consistent with photosynthesis and photoacclimation theories. The natural phytoplankton communities studied were in a photoprotective state for blue wavelengths (440 and 480 nm), but not for other wavelengths (green (540 nm), amber (590 nm) and light red (625 nm)). Population-detrended PETλ values were then used in multivariate analyses (partial triadic analysis and redundancy analysis) to study ecological implications of PETλ dynamics among water masses. Two wavelength ratios based on the microalgae saturation parameter Ek (in relative and absolute units), related to the hydrodynamic regime and underwater light climate, clearly confirmed the physiological state of microalgae. They also illustrate more accurately that natural phytoplankton communities can implement photoacclimation processes that are influenced by in situ light quality during the daylight cycle in temporarily and weakly stratified water. Ecological implications and consequences of PETλ are discussed in the context of turbulent coastal ecosystems.

Depth diversity gradients of macrophytes: Shape, drivers, and recent shifts.

Investigating diversity gradients helps to understand biodiversity drivers and threats. However, one diversity gradient is rarely assessed, namely how plant species distribute along the depth gradient of lakes. Here, we provide the first comprehensive characterization of depth diversity gradient (DDG) of alpha, beta, and gamma species richness of submerged macrophytes across multiple lakes. We characterize the DDG for additive richness components (alpha, beta, gamma), assess environmental drivers, and address temporal change over recent years. We take advantage of yet the largest dataset of macrophyte occurrence along lake depth (274 depth transects across 28 deep lakes) as well as of physiochemical measurements (12 deep lakes from 2006 to 2017 across Bavaria), provided publicly online by the Bavarian State Office for the Environment. We found a high variability in DDG shapes across the study lakes. The DDGs for alpha and gamma richness are predominantly hump‐shaped, while beta richness shows a decreasing DDG. Generalized additive mixed‐effect models indicate that the depth of the maximum richness (D max) is influenced by light quality, light quantity, and layering depth, whereas the respective maximum alpha richness within the depth gradient (R max) is significantly influenced by lake area only. Most observed DDGs seem generally stable over recent years. However, for single lakes we found significant linear trends for R max and D max going into different directions. The observed hump‐shaped DDGs agree with three competing hypotheses: the mid‐domain effect, the mean–disturbance hypothesis, and the mean–productivity hypothesis. The DDG amplitude seems driven by lake area (thus following known species–area relationships), whereas skewness depends on physiochemical factors, mainly water transparency and layering depth. Our results provide insights for conservation strategies and for mechanistic frameworks to disentangle competing explanatory hypotheses for the DDG.

Community shifts from eukaryote to cyanobacteria dominated phytoplankton: The role of mixing depth and light quality

Abstract Lake stratification strengthens with increasing surface water temperatures, thereby reducing the depth of the mixed layer. Phytoplankton communities are not only exposed to different nutrient availability within a mixed water column, but also to different light quality. We conducted controled laboratory and mesocosm experiments to investigate phytoplankton, especially cyanobacteria, responses to different light quality and mixing depths. Our mesocosm experiment allowed the manipulation of mixing depth in situ by a mesocosm approach and to follow the effects of changing mixing depth on the phytoplankton community composition. Our laboratory experiment allowed the control of temperature and light quantity. To investigate the effect of light quality on phytoplankton, we created a light gradient from full photosynthetic active radiation to a reduced blue spectrum. In both experiments, shifts in phytoplankton community composition from eukaryote to cyanobacteria occurred at shallow mixing depth with higher availability of photosynthetic active radiation. Our results from the mesocosm experiment support the idea that reduced mixing depth can promote cyanobacterial abundance. With our laboratory experiment, we were able to manipulate light quality independent of temperature, available nutrients and light intensity influencing phytoplankton abundance. Results from the laboratory experiments support our hypothesis that a shift in light spectrum alone is a driver, strong enough to enhance cyanobacteria occurrence. Most of the previous studies dealing with cyanobacterial blooms have investigated temperature and eutrophication effects. Certainly, these are major factors for the growth of phytoplankton, but our experiments show that other aspects, such as the quality of light, must be also taken into account to explain cyanobacterial blooms. Such shifts in the phytoplankton community from eukaryote to cyanobacteria dominated communities will have strong consequences for food web dynamics. Several cyanobacteria specific traits, (e.g., toxin production, lack of essential fatty acids, and inedibility through production of large colonies) reduce transfer efficiencies of energy and matter between phyto‐ and zooplankton and therefore can influence higher trophic levels such as fish.

Light-dependent impact of salinity on the ecophysiology of Synechococcus elongatus PCC 7942: Genetic and comparative protein structure analyses of UV-absorbing mycosporine-like amino acids (MAAs) biosynthesis

Cyanobacteria are subjected to a dynamic light environment in their natural habitat or artificial cultivation system. The fluctuating light environment is associated with increased salinity stress due to the evaporation of the growth medium. Therefore, it is important to understand the physiology of the organisms under a dynamic environment of light and salinity which together affect the fitness and overall performance of the organism. We studied the growth behavior and other physiological parameters of Synechococcus elongatus PCC 7942 in the presence of different NaCl concentrations (0, 50, 100 and 200 mM) and light conditions such as low PAR (LPAR), high PAR (HPAR) and PAR + UVR using diurnal and continuous photoperiods. We also investigated the ability of S. elongatus PCC 7942 to biosynthesize UV-absorbing mycosporine-like amino acids (MAAs) and conducted genetic and comparative protein structure analyses to better understand its biosynthesis. Results obtained suggest that the impact of salinity stress caused by NaCl on growth behavior and physiological parameters such as photosynthetic pigments, the effective quantum yield of PSII and oxidative stress is dependent on the light environment. These parameters were affected differently by the quality and quantity of light and photoperiods, and the negative effect of salinity was alleviated by a high light environment. S. elongatus PCC 7942 does not biosynthesize MAAs due to the absence of MAAs biosynthesizing genes cluster in its genome. Results from genomic and comparative protein structure analyses suggested that DDGS and DHQS enzymes are different and DDGS but not DHQS is required for MAAs biosynthesis. Understanding the light-dependent impact of salinity stress may help in developing strategies for outdoor cultivation of cyanobacteria for bioenergy and valuable chemicals production by balancing absorbed and utilized radiant energy.

Shining a light on Laurentian Great Lakes cisco (Coregonus artedi): How ice coverage may impact embryonic development☆

Changes in winter conditions, such as decreased ice coverage and duration, have been observed in the Laurentian Great Lakes for more than 20 years. Such changes have been hypothesized to be linked to low Coregonus spp. survival to age-1 as most cisco (Coregonus artedi) populations are autumn spawners whose embryos incubate under ice throughout the winter. The quantity of light during winter is regulated by ice coverage, and light affects embryo survival and development in some teleosts. We experimentally evaluated how cisco embryos from lakes Superior and Ontario respond to three light treatments that represented day-light intensity under 0–10, 40–60, and 90–100% ice coverage. Embryonic response measures included two developmental factors (embryo survival and incubation period) and two morphological traits (length-at-hatch and yolk-sac volume). Embryo survival was highest at the medium light treatment and decreased at high and low treatments for both populations, suggesting cisco may be adapted to withstand some light exposure from inter-annual variability in ice coverage. Light intensity had no overall effect on length of incubation. Increasing light intensity decreased length-at-hatch in Lake Superior but had no effect in Lake Ontario. Yolk-sac volume was positively correlated with increasing light in Lake Superior and negatively correlated in Lake Ontario. Contrasting responses in embryo development between lakes suggests differences in populations’ response to light is flexible. Our results provide a step towards better understanding the high variability observed in coregonine recruitment and may help predict what the future of this species may look like under current climate trends.

Process Parameter Screening for the Microalga Chlamydomonas asymmetrica in Batch and Turbidostat Cultivations

AbstractAlgae offer tremendous potential for the production of various high‐value products (HVPs). Besides the light quantity and quality, factors such as temperature, medium composition, pH, and aeration are important algae‐specific process parameters that influence growth behavior and their chemical composition. Screenings for algae and their HVPs are ongoing, but the available data for their cultivability and suitability as production organisms are limited. Turbidostat processes enable a simple and fast screening for light‐specific influences, as constant biomass concentrations will result in constant self‐shading. Here, the microalgae Chlamydomonas asymmetrica was cultivated in cylindrical photobioreactor screening modules. A detailed characterization the light and temperature dependency of the organisms' HVPs is provided.

Lighting quantity indexes for lighting traditional Chinese paintings based on pigments protection and substrates protection in museums.

In museum lighting, traditional Chinese paintings are the artworks with the highest light sensitivity. They are vulnerable to the color damage to pigments and the mechanical damage to substrates after the irradiation from light sources. As the basis of effective preventive protection, the research on the two lighting quantity indexes of illuminance and annual exposure (illuminance × time) is currently missing. In this study, the halogen lamp was used as the experimental light source to conduct a 1440 h irradiation experiment on the samples of paper and silk substrates under 4 illuminance levels, respectively, and the test of infrared spectrum was carried out on the samples every 240 h. The oxidation index of paper and crystallinity degree of silk were calculated then. Three-dimensional visual curved surface plots of mechanical damage to samples with the change of illuminance and time were established and then fitted into damage evaluation equations, which revealed and described mathematically the mechanical damage law of samples. Through the equations, the recommended values of illuminance and annual exposure for samples could be calculated. Combining the previous researches on pigments, the lighting quantity indexes of traditional Chinese paintings with different combinations of substrates and pigments were proposed.

A study on the factors simultaneously affecting visual comfort in classrooms: A structural equation modeling approach

Various environmental, architectural, and individual factors other than quantity and quality of light, affect pupils' visual comfort in the classrooms. The simultaneous effect of these factors on visual perception is more substantial than the individual impact of each. In this study, an Structural Equation Model (SEM) technique systematically explains students' visual comfort evaluation. It quantifies the effects and values of various factors that directly and indirectly affect classroom visual comfort.The survey is designed to evaluate all the variables of the conceptual model. 192 students in a high school in Tehran participated in this survey. Field measurement and simulation were conducted to gather physical parameters data. As a result, the proposed partial least square-structural equation model (PLS-SEM) model showed statistical significance and a high model fitness level (GoF = 0.547). It is confirmed that overall visual comfort is significantly affected by twelve studied variables such as glare sensation and perceived lighting level. Among these, the lighting level has the highest importance, while view satisfaction has the lowest in this visual comfort model. In south classrooms, electricity load (6.5%) and satisfaction level (6.0%) are higher than in the north in June. The findings of this study help to provide valuable insights for improving visual comfort in classrooms.

Physiological and ecological consequences of the water optical properties degradation on reef corals

Degradation of water optical properties due to anthropogenic disturbances is a common phenomenon in coastal waters globally. Although this condition is associated with multiple drivers that affect corals health in multiple ways, its effect on light availability and photosynthetic energy acquisition has been largely neglected. Here, we describe how declining the water optical quality in a coastal reef exposed to a turbid plume of water originating from a man-made channel compromises the functionality of the keystone coral species Orbicella faveolata. We found highly variable water optical conditions with significant effects on the light quantity and quality available for corals. Low-light phenotypes close to theoretical limits of photoacclimation were found at shallow depths as a result of reduced light penetration. The estimated photosynthetically fixed energy depletion with increasing depth was associated with patterns of colony mortality and vertical habitat compression. A numerical model illustrates the potential effect of the progressive water quality degradation on coral mortality and population decline along the depth gradient. Collectively, our findings suggest that preserving the water properties seeking to maximize light penetration through the water column is essential for maintaining the coral reef structure and associated ecosystem services.

The influence of photoselective shade netting on vegetative growth and bioactivity of Myrsine africana L. for cosmeceutical production

As the global desire for natural remedies derived from botanicals increases, the pressure on plant populations and biodiversity intensifies. Therefore, to conserve biodiversity as a valuable genetic and biochemical resource, sustainable utilisation and commercial production should be prioritised. Myrsine africana L. (MA), has recently been found to possess significant cosmeceutical properties, such as elastase inhibition (anti-wrinkle) and anti-tyrosinase (skin even tone) activity. However, this species is relatively slow growing, recalcitrant to adventitious root (AR) development, and has slightly insufficient bioactivity in raw extracts. These factors reduce the economic feasibility of producing this commercially valuable indigenous species. Consequently, this may enhance wild harvesting of this species, placing pressure on wild populations. Manipulation of light is a common practice in plant production to exploit plant growth and development, as light quantity and quality effectively influence the primary and secondary metabolism of plants. Therefore, the current study aimed to investigate the influence of selected photoselective shade net on vegetative growth and metabolites of MA shoot material. Results displayed significantly enhanced growth (p < 0.001) under green (50 % density), black (50 %) and red (80 %) shade net in comparison to the control (cultivation under full sun) and inhibited growth under blue (50 %) shade net. Shade net effectively influenced starch and soluble carbohydrate content. Furthermore, significantly higher elastase inhibition was observed under green and red shade net treatments in comparison to the control in autumn, with IC50 values of 18.59 μg/mL, 19.28 μg/mL and 37.93 μg/mL, respectively. In addition, bioactivity was significantly higher in autumn (p < 0.001) under green, red and control treatments. It can be concluded that photoselective shade net may be used to enhance plant growth and bioactivity of MA.

The Potential of High-Anthocyanin Purple Rice as a Functional Ingredient in Human Health.

Purple rice is recognized as a source of natural anthocyanin compounds among health-conscious consumers who employ rice as their staple food. Anthocyanin is one of the major antioxidant compounds that protect against the reactive oxygen species (ROS) that cause cellular damage in plants and animals, including humans. The physiological role of anthocyanin in plants is not fully understood, but the benefits to human health are apparent against both chronic and non-chronic diseases. This review focuses on anthocyanin synthesis and accumulation in the whole plant of purple rice, from cultivation to the processed end products. The anthocyanin content in purple rice varies due to many factors, including genotype, cultivation, and management as well as post-harvest processing. The cultivation method strongly influences anthocyanin content in rice plants; water conditions, light quantity and quality, and available nutrients in the soil are important factors, while the low stability of anthocyanins means that they can be dramatically degraded under high-temperature conditions. The application of purple rice anthocyanins has been developed in both functional food and other purposes. To maximize the benefits of purple rice to human health, understanding the factors influencing anthocyanin synthesis and accumulation during the entire process from cultivation to product development can be a path for success.

Rapid changes in spectral composition after darkness influences nitric oxide, glucose and hydrogen peroxide production in the Antarctic diatom Fragilariopsis cylindrus

Ice-associated phototrophic taxa contribute significantly to Antarctic primary production and are crucial to ecosystem stability in the Southern Ocean. The quantity and quality of light required for photosynthesis is the single most influential driver of ice-associated algal communities. While the presence of ice and snow greatly reduces the irradiance reaching the ice-water interface, it is also the spectral quality that influences the phototrophy of ice-associated microalgae communities. Here we test the capability of three electrochemical microsensors to detect photosynthetically derived “stress” metabolites produced by the Antarctic diatom F. cylindrus. Following a period of dark incubation, this photo-physiological response differed with respect to the intensity and spectral quality of light during re-illumination. Exposure to blue light resulted in impairment in photosynthetic efficiency of PSII (Fv/Fm) and resulted in the production of nitric oxide (NO), hydrogen peroxide (H2O2) and glucose exudation. A similar trend in metabolite production was observed when subjected to white light, but not during red or green illumination. These results indicate that rapid exposure to light and variation in spectral composition can cause significant stress that can be quantified using H2O2, NO and glucose microsensors. This metabolic overflow was triggered by the disruption of normal photosynthetic electron flow and it is proposed that the detection of extracellular metabolites can be directly attributed to intracellular activity.

Light quality and quantity affect graft union formation of tomato plants

It is already known that there are many factors responsible for the successful formation of a graft union. However, the role of light has been little studied. In an anatomical study, Scanning Electronic Microscope (SEM) was used to explore the effects of different light-emitting diodes (LEDs) on graft union formation in grafted tomato. In addition, the expression genes related to Auxin hormone signaling pathway (SAUR67, AUX1, ARF30, and LAX3) was investigated. The obtained results showed that the concrescence process occurred faster under R7:B3 light conditions, as compared to blue (B) and white fluorescent (WFL) lights. Red light application caused a delay in the vascular tissue differentiation, which may lead to callus development on both sides, causing junctional failure and resulting in ineffective graft junctional arrangement. The expression of genes related to Auxin hormone significantly increased by R7:B3 application. We suggest that LED spectra affects the graft development of tomato plants and can improve the performance of grafted tomato seedlings.

Optimization of Ag2S Quantum Dots Decorated ZnO Nanorod Array Photoanodes for Enhanced Photoelectrochemical Performances

The synthesis of Ag2S quantum dots (QDs) deposited on the surface of electrodeposited ZnO nanorods (NRs) by a successive ionic-layer adsorption and reaction (SILAR) method is reported. A Box-Behnken response surface factorial design was used to organize the experiments conducted and identify the effects of three electrochemical parameters and their potential interactions. These parameters include zinc precursor concentration in the electrolytic bath, the electrolytic bath temperature and the electrodeposition time on the morphological and structural properties of the electrochemically grown ZnO nanorods. Morphological, structural and optical characterizations of these NRs heterojunctions were done. A direct band gap for Ag2S QDs, tuned between 2.54 and 2.73 eV by varying the SILAR cycle numbers, was determined. The presence of ZnO nanostructures increases the light scattering capability of the samples, allowing an important quantity of diffuse light near the absorption edge of Ag2S. The photoelectrochemical performance of these ZnO NRs decorated with Ag2S QDs based photoanodes has been evaluated. The SILAR parameters related to the growth of the Ag2S QDs that optimize the performance of this photoelectrode are presented. The effect of a ZnS passivation layer has been studied leading to an increase of about 400% in the short-circuit current density after passivation.

Apple tree adaptation to shade in agroforestry: an architectural approach.

The expression of shade adaptation traits is expected to be stronger in low light and can be detrimental to flowering and yield. Our study focused on the expression of shade adaptation traits of apple trees (Malus domestica Borkh. 'Dalinette') in an agroforestry system. The architecture of 45 apple trees in their third and fourth year was extensively described and analyzed at the tree scale and compared depending on the light quantity received during the growing season. Flower cluster phenology and the relation between leaf area and floral initiation were also investigated. The number of growing shoots and the leaf area were reduced by shade even if specific leaf area increased with increasing shade. Shade did not modify primary growth but did decrease secondary growth, so that apple tree shoots in shade were slender, with a lower taper and reduced number and proportion of flower clusters. The correlation between floral initiation and leaf area was high both in full and moderate light but not for apple trees in low light. Shade did not impact the date of bud burst and the early phenological stages of flower clusters, but it reduced the number of days at full bloom. Our results suggest that while the architecture of apple trees is modified by a reduction in light intensity, it is not until a reduction of 65% that the capability to produce fruit is impeded. These results could help optimize the design of apple-tree-based agroforestry systems.

Photosynthesis and Bio-Optical Properties of Fluorescent Mesophotic Corals

Mesophotic coral ecosystems (MCEs) are light-dependent coral-associated communities found at 30–150 m depth. Corals inhabiting these deeper reefs are often acclimatized to a limited and blue-shifted light environment, enabling them to maintain the relationship with their photosynthetic algal symbionts (family Symbiodiniaceae) despite the seemingly suboptimal light conditions. Among others, fluorescent proteins produced by the coral host may play a role in the modulation of the quality and spectral distribution of irradiance within the coral tissue through wavelength transformation. Here we examined the bio-optical properties and photosynthetic performances of different fluorescence morphs of two mesophotic coral species Goniopora minor and Alveopora ocellata, in order to test the photosynthesis enhancement hypothesis proposed for coral fluorescence. The green morph of G. minor and the low fluorescence morph of A. ocellata exhibit, in their natural habitats, higher abundance. The morphs also presented different spectral reflectance and light attenuation within the tissue. Nevertheless, chlorophyll a fluorescence-based, and O2 evolution measurements, revealed only minor differences between the photosynthetic abilities of three fluorescence morphs of the coral G. minor and two fluorescence morphs of A. ocellata. The fluorescence morphs did not differ in their algal densities or chlorophyll concentrations and all corals harbored Symbiodiniaceae from the genus Cladocopium. Thus, despite the change in the internal light quantity and quality that corals and their symbionts experience, we found no evidence for the facilitation or enhancement of photosynthesis by wavelength transformation.

Do sexual gonadic maturity and age determine habitat occupancy ofCanthon cyanellusLeConte, 1859 (Coleoptera: Scarabaeidae)?

AbstractHigh-quality habitats presumably have the resources required to sustain relatively high rates of survival and reproduction. We assessed how habitat type and local environmental conditions determine the distribution of individuals ofCanthon cyanellus(Coleoptera: Scarabaeidae), an eurytopic dung beetle, according to age category and sexual gonadic maturity. Beetles were surveyed in forest fragments, live fences, and pastures in Mexico. Individuals were categorised into six age categories according to the glandular volumes in males and oocyte number and length in females. Mature females in forest fragments were the most abundant females found among the habitats. Air humidity and soil hardness were positively and negatively related to mature female abundance, respectively. Mature beetles were the most abundant among males, and higher abundance of males occurred in forest fragments than in live fences and pastures. Light quantity was negatively related to the abundance of young males. Compared to forest fragments, females in pastures had larger oocytes. However, sites with higher soil hardness and air humidity had females with lower numbers of oocytes. Our results demonstrate that, althoughC. cyanellusoccurs across a wide range of habitats, forest habitats might host sexually mature individuals, which translates into more effective individual dispersion and potential reproduction.

Effect of Asynchronous Light and Temperature Fluctuations on Plant Traits in Indoor Growth Facilities

Several studies have recommended the incorporation of environmental fluctuations in indoor experiments if closer-to-natural results in plant experiments are desired. Previous authors have suggested that if these fluctuations are not applied in synchrony, a stress effect could be present since plants have evolved to cope with synchronic environmental fluctuations. This study aimed to identify the effect of disparity in fluctuations of two important environmental variables, light quantity and temperature, on the growth of seven plant species from different functional plant types. A full-factorial combination of light and temperature under fixed or variable conditions was applied in phytotrons, and plant performance under these conditions was compared with a previous field trial. In all phytotron treatments, the average light and temperature conditions were the same as in the initial field trial. Productivity, leaf gas exchange, chlorophyll fluorescence, pigmentation, and other leaf traits were recorded in all species at the end of the experiments. Most plant trait responses were highly dependent on species and treatment, but some general trends were observed. Light fluctuations were mainly responsible for increases in specific leaf area (SLA) and chlorophyll a concentration, as well as for reductions in total dry weight and chlorophyll a/b ratio, independent if in combination with fluctuation or fixed temperatures. When fixed light conditions were combined with variable temperatures, the plants showed on average lower Fv/Fm values, Amax, and CO2 yield, while under variable light conditions and fixed temperatures, Fv/Fm increased compared with fully fixed or variable conditions. Although significant differences of plant traits between the field trial and all phytotron treatments were present (likely due to differences in other parameters that were not controlled in the phytotrons), our results still suggest that a synchronous variation of environmental factors lead to a more natural-like plant growth than if these factors are fixed or vary asynchronously.

Effect of Multispectral Pulsed Light-Emitting Diodes on the Growth, Photosynthetic and Antioxidant Response of Baby Leaf Lettuce (Lactuca sativa L.).

The effect of multicolor pulsed light-emitting diode (LED) irradiation on lettuce “Defender” growth, photosynthetic performance and antioxidant properties was studied. The experiments were designed to compare the continuous and pulsed lighting (0.5, 1 kHz; 50% duty ratio) effects of B450, G520, R660 and FR735 lighting components, maintaining total diurnal integral light quantity (DLI 14.4 mol m−2 day−1) constant during the 16-h photoperiod. The results showed that lettuce grown under pulsed irradiation displayed superior growth performance, including a significant enhancement of fresh (~32%) and dry biomass (~36%) and leaf area (~48%). Lettuce cultivated in both pulsed light treatments was characterized by the higher photosynthetic rate, chlorophyll (a,b) and carotenoid concentration. However, the total phenol and antioxidant properties in lettuce were more dependent on the specific pulsed light frequency. Only treatment with 1 kHz frequency was effective for higher phenol content, 2,20-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) (ABTS) free radical scavenging activity and Fe2+ reducing antioxidant power (FRAP). Thus, our results propose the role of pulsed LED light in improving the photosynthetic efficiency and antioxidative properties of lettuce plants cultivated indoors. In the future, pulsed lighting techniques should be included in the development of artificial lighting systems in controlled environment agriculture (CEA) to produce high-quality crops with the possibility to save electricity.