Light Spectral Quality Research Articles

Response of Cyanic and Acyanic Lettuce Cultivars to an Increased Proportion of Blue Light.

Simple SummaryIndoor crop cultivation systems such as vertical farms or plant factories necessitate artificial lighting. The composition of light quality (i.e., spectral composition) within these systems plays a key role in crop growth and development. Conflicting results on the effects of the light spectrum reported for different plant species and cultivars confirm the specificity of light requirements and the dependency on interacting factors. In this paper, we have therefore investigated how a certain light quality (light with a high share of blue) affects photosynthetic and morphological parameters in two contrasting lettuce cultivars (red and green leaves) with a similar leaf shape and phenotype. The results obtained suggest the occurrence of distinctive morpho-physiological adaptive strategies in green and red pigmented lettuce cultivars to adapt to the higher proportion of blue light environment.Indoor crop cultivation systems such as vertical farms or plant factories necessitate artificial lighting. Light spectral quality can affect plant growth and metabolism and, consequently, the amount of biomass produced and the value of the produce. Conflicting results on the effects of the light spectrum in different plant species and cultivars make it critical to implement a singular lighting solution. In this study we investigated the response of cyanic and acyanic lettuce cultivars to an increased proportion of blue light. For that, we selected a green and a red leaf lettuce cultivar (i.e., ‘Aquino’, CVg, and ‘Barlach’, CVr, respectively). The response of both cultivars to long-term blue-enriched light application compared to a white spectrum was analyzed. Plants were grown for 30 days in a growth chamber with optimal environmental conditions (temperature: 20 °C, relative humidity: 60%, ambient CO2, photon flux density (PFD) of 260 µmol m−2 s−1 over an 18 h photoperiod). At 15 days after sowing (DAS), white spectrum LEDs (WW) were compared to blue-enriched light (WB; λPeak = 423 nm) maintaining the same PFD of 260 µmol m−2 s−1. At 30 DAS, both lettuce cultivars adapted to the blue light variant, though the adaptive response was specific to the variety. The rosette weight, light use efficiency, and maximum operating efficiency of PSII photochemistry in the light, Fv/Fm’, were comparable between the two light treatments. A significant light quality effect was detected on stomatal density and conductance (20% and 17% increase under WB, respectively, in CVg) and on the modified anthocyanin reflectance index (mARI) (40% increase under WB, in CVr). Net photosynthesis response was generally stronger in CVg compared to CVr; e.g., net photosynthetic rate, Pn, at 1000 µmol m−2 s−1 PPFD increased from WW to WB by 23% in CVg, compared to 18% in CVr. The results obtained suggest the occurrence of distinct physiological adaptive strategies in green and red pigmented lettuce cultivars to adapt to the higher proportion of blue light environment.

Controllable Phycobilin Modification: An Alternative Photoacclimation Response in Cryptophyte Algae

Cryptophyte algae are well-known for their ability to survive under low light conditions using their auxiliary light harvesting antennas, phycobiliproteins. Mainly acting to absorb light where chlorophyll cannot (500–650 nm), phycobiliproteins also play an instrumental role in helping cryptophyte algae respond to changes in light intensity through the process of photoacclimation. Until recently, photoacclimation in cryptophyte algae was only observed as a change in the cellular concentration of phycobiliproteins; however, an additional photoacclimation response was recently discovered that causes shifts in the phycobiliprotein absorbance peaks following growth under red, blue, or green light. Here, we reproduce this newly identified photoacclimation response in two species of cryptophyte algae and elucidate the origin of the response on the protein level. We compare isolated native and photoacclimated phycobiliproteins for these two species using spectroscopy and mass spectrometry, and we report the X-ray structures of each phycobiliprotein and the corresponding photoacclimated complex. We find that neither the protein sequences nor the protein structures are modified by photoacclimation. We conclude that cryptophyte algae change one chromophore in the phycobiliprotein β subunits in response to changes in the spectral quality of light. Ultrafast pump–probe spectroscopy shows that the energy transfer is weakly affected by photoacclimation.

Light Pollution and Circadian Misalignment: A Healthy, Blue-Free, White Light-Emitting Diode to Avoid Chronodisruption.

Sunlight has participated in the development of all life forms on Earth. The micro-world and the daily rhythms of plants and animals are strongly regulated by the light–dark rhythm. Human beings have followed this pattern for thousands of years. The discovery and development of artificial light sources eliminated the workings of this physiological clock. The world’s current external environment is full of light pollution. In many electrical light bulbs used today and considered “environmentally friendly,” such as LED devices, electrical energy is converted into short-wavelength illumination that we have not experienced in the past. Such illumination effectively becomes “biological light pollution” and disrupts our pineal melatonin production. The suppression of melatonin at night alters our circadian rhythms (biological rhythms with a periodicity of 24 h). This alteration is known as chronodisruption and is associated with numerous diseases. In this article, we present a blue-free WLED (white light-emitting diode) that can avoid chronodisruption and preserve circadian rhythms. This WLED also maintains the spectral quality of light measured through parameters such as CRI (color reproduction index).

Effects of Light Spectral Quality on Photosynthetic Activity, Biomass Production, and Carbon Isotope Fractionation in Lettuce, Lactuca sativa L., Plants.

The optimization of plant-specific LED lighting protocols for indoor plant growing systems needs both basic and applied research. Experiments with lettuce, Lactuca sativa L., plants using artificial lighting based on narrow-band LEDs were carried out in a controlled environment. We investigated plant responses to the exclusion of certain spectral ranges of light in the region of photosynthetically active radiation (PAR); in comparison, the responses to quasimonochromatic radiation in the red and blue regions were studied separately. The data on plant phenotyping, photosynthetic activity determination, and PAM fluorometry, indicating plant functional activity and stress responses to anomalous light environments, are presented. The study on carbon isotopic composition of photoassimilates in the diel cycle made it possible to characterize the balance of carboxylation and photorespiration processes in the leaves, using a previously developed oscillatory model of photosynthesis. Thus, the share of plant photorespiration (related to plant biomass enrichment with 13C) increased in response to red-light action, while blue light accelerated carboxylation (related to 12C enrichment). Blue light also reduced water use efficiency. These data are supported by the observations from the light environments missing distinct PAR spectrum regions. The fact that light of different wavelengths affects the isotopic composition of total carbon allowed us to elucidate the nature of its action on the organization of plant metabolism.

High Tunnel Coverings Alter Crop Productivity and Microclimate of Tomato and Lettuce

The implementation of high tunnels has shown to increase marketability and/or yield of tomato (Solanum lycopersicum) and lettuce (Lactuca sativa) crops compared with open-field systems. These structures provide the opportunity to alter light intensity and spectral quality by using specific polyethylene (poly) films and/or shadecloth, which may affect microclimate and subsequent crop productivity. However, little is known about how specific high tunnel coverings affect these parameters. The overall goal of this study was to evaluate the impact of various high tunnel coverings on the microclimate and crop productivity of tomato and lettuce. The coverings included standard, ultraviolet (UV)-stabilized poly film (standard); diffuse poly (diffuse); full-spectrum clear poly (clear); UV-A/B blocking poly (block); standard + 55% shadecloth (shade); and removal of standard poly 2 weeks before initial harvest to simulate a movable tunnel (movable). Microclimate parameters that were observed included canopy and soil temperatures, canopy growing degree-days (GDD), and photosynthetic active radiation (PAR), and crop productivity included yield and net photosynthetic rate. Hybrid red ‘BHN 589’ tomatoes were grown during the summer, and red ‘New Red Fire’ and green ‘Two Star’ leaf lettuce were grown in both spring and fall in 2017 and 2018. Increased temperature, GDD, and PAR were observed during the spring and summer compared with the fall. The soil temperatures during the summer increased more under the clear covering compared with the others. For tomato, the shade produced lower total fruit yield and net photosynthetic rate (Pn) compared with the other treatments, which were similar (P < 0.001 and <0.001, respectively). The greatest yield was 7.39 kg/plant, which was produced under the clear covering. For red leaf lettuce grown in the spring, the plants under the clear, standard, and diffuse coverings had significantly greater yield than the movable and shade coverings (P < 0.001). The coverings had less effect on the yield during the fall lettuce trials, which may have been attributed to the decrease in PAR and environmental temperatures. The findings of this study suggest that high tunnel coverings affect both microclimate and yield of lettuce and tomato.

Spectral Light Quality Regulates Morphogenesis, Architecture, and Flowering of Pepper Plants

Spectral Light Quality Regulates Morphogenesis, Architecture, and Flowering of Pepper Plants

Effects of spectral light quality on the growth, productivity, and elemental ratios in differently pigmented marine phytoplankton species

The recent advancement in LED technology led many incubator manufacturers and research labs to switch to these more efficient, yet spectrally restricted, light sources. Potential effects of commercially available broad range “white” light systems on phytoplankton growth, productivity, light absorption spectra, and cellular composition have not yet been characterized but could affect our interpretation of lab-based projections on responses to environmental changes. In this study, we investigated such effects using cultures of Prochlorococcus marinus, Synechococcus sp., and Thalassiosira weissflogii grown under three different commercially available LED lights as well as one fluorescent growth light. Photosynthetically active radiation was equal for each species, while photosynthetically usable radiation differed among the combinations of species and treatments. Growth rate was unaffected across species, yet all species displayed changes in cellular carbon, nitrogen, and chlorophyll a quotas as a direct response to the different light spectra. 14C-based primary productivity was also affected in P. marinus and T. weissflogii. Analysis of pigment ratios and photophysiological data indicated changes in the photoacclimation state between different light environments. The results of this study show that these species undergo changes in underlying cellular metabolism which in turn affect cellular composition while keeping specific growth constant. The data presented here illustrate ecophysiological responses of differently pigmented species when grown under different artificial growth light spectra. These cellular acclimation responses should be considered when designing laboratory-based incubation experiments, especially when comparing responses to specific changes in environmental conditions, or when implementing physiological parameters, derived from laboratory experiments, into numerical models.

Fullerene-Filtered Light Spectrum and Fullerenes Modulate Emotional and Pain Processing in Mice

The most symmetric molecule, Buckminster fullerene C60, due to its unique properties, has been intensively studied for various medical and technological advances. Minimally invasive and minimally toxic treatments hold great promise for future applications. With this in mind, this research exploited the physical properties of fullerene molecules for potential therapeutic effects. Pristine fullerenes have peak absorbance in the 380–500 nm range, making them an attractive violet-blue light filter. Since spectral quality of light can affect behavior, this research used resting state functional magnetic resonance imaging (rs fMRI) and behavioral testing to directly evaluate the effects of fullerene-filtered light on brain processing and behavior in mice. The same method was used to study if hydroxyl fullerene water complexes (3HFWC), with or without fullerene-filtered light, modulated brain processing. A month-long, daily exposure to fullerene-filtered light led to decreased activation of the brain area involved in emotional processing (amygdala). Water supplemented with 3HFWC resulted in an activation of brain areas involved in pain modulation and processing (periaqueductal gray), and decreased latency to first reaction when tested with a hot plate. The combination of fullerene-filtered light with 3HFWC in drinking water led to restored sensitivity to a hot plate and activation of brain areas involved in cognitive functions (prelimbic, anterior cingulate and retrosplenial cortex). These results uncovered the potential of fullerene-filtered light to impact emotional processing and modulate pain perception, indicating its further use in stress and pain management.

Imaging Radiotherapy-Induced Cherenkov Emission in Color

<h3>Purpose/Objective(s)</h3> In the last decade, Cherenkov imaging has been demonstrated as a useful clinical technique both for real-time surface dose visualization during patient treatment and for various high-resolution QA measurements. However there remains much work to be done in the development of Cherenkov-based in vivo dosimetry. In this work, the concept of in vivo color Cherenkov imaging is introduced. It is hypothesized that Cherenkov images with sensitivity to the spectral quality of Cherenkov emission induced inside tissue can provide increased information about tissue composition as opposed to monochromatic, red-weighted images used in prior work. <h3>Materials/Methods</h3> A custom Color Cherenkov camera was created from three time-gated intensified CMOS cameras, each with varying spectral sensitivity of the photocathode, and sharing one imaging lens. A dichroic mirror assembly allowed for incoming Cherenkov light signals to be redirected according to wavelength to the appropriate camera resulting in three raw image stacks for each acquisition. These images were then reconstructed into three-channel color images via color calibration, summed, and background subtracted. In vivo color Cherenkov images of three right-sided breast patients were acquired for one treatment fraction each as part of an IRB-approved clinical trial. These images were interpreted alongside images of liquid tissue-simulating phantoms that matched tissue optical properties. Variations in oxygenation and blood volume were mimicked in this way, and the data was used to interpret the clinical images. Impacts on Cherenkov emission spectra from tissue under these various conditions were also estimated. <h3>Results</h3> The presence of oxygenated vs deoxygenated blood in tissue has a visible impact on the color of Cherenkov emission, leading to a redder hue due to decreased attenuation of red wavelengths by oxyhemoglobin, similar to erythema or blush of tissue. This was verified in the tissue phantoms. Variations in blood concentration produce a strong blue-red trend in color space (R² = 0.96), as verified by detailed analysis. Color Cherenkov images of right breast radiotherapy treatments displayed pink regions across the breast coincident with the treated area for all three patients, and the variations in color were interpreted relative to the phantom data. <h3>Conclusion</h3> This first investigation of color Cherenkov imaging uncovered the natural relationship between tissue composition and the spectral quality of emitted Cherenkov light. The correlation between blood content and color will be translated in future work to in vivo sensing of variations in fat and fibroglandular content in irradiated tissues. These findings will allow for the correction of Cherenkov images to produce accurate in vivo surface dose maps during patient treatments.

Effect of combined light-emitting diodes on the accumulation of glucosinolates in Brassica microgreens

As of recent, microgreen vegetable production in controlled environments are being investigated for their bioactive properties. Phytochemicals like glucosinolates (GLS) are highly sensitive to varying spectral qualities of light, especially in leafy greens of Brassica where the responses are highly species-dependent. The accumulation of bioactive GLS were studied under 8 different treatments of combined amber (590 nm), blue (455 nm), and red (655 nm) light-emitting diodes (rbaLED). A semi-targeted metabolomics approach was carried out to profile common intact-GLS in microgreen extracts of Brassica by means of LC-HRMS/MS. Thirteen GLS were identified, among them were 8 aliphatic, 4 indolic and 1 aromatic GLS. Mass spectrometry data showed sinigrin had the highest average concentration and was highest in B. juncea, progoitrin was highest in B. rapa and glucobrassicin in R. sativus. The individual and total GLS in the microgreens of the present study were largely different under rbaLED; B. rapa microgreens contained the highest profile of total GLS, followed by R. sativus and B. juncea. Sinigrin was increased and gluconasturtiin was decreased under rbaLED lighting in most microgreens, glucoalyssin uniquely increased in R. sativus and decreased in B. rapa and glucobrassicin uniquely decreased in both B. rapa and B. juncea. The present study showed that rbaLED contributed to the altered profiles of GLS resulting in their significant modulation. Optimizing the light spectrum for improved GLS biosynthesis could lead to production of microgreens with targeted health-promoting properties.Graphical

Effects of Light Spectral Quality on the Micropropagated Raspberry Plants during Ex Vitro Adaptation.

This work focuses on developing light environments for the effective regulation of morphogenesis and ex vitro conditions adaptation in micropropagated raspberry plants on the basis of photomorphogenetic control of physiological processes using light-emitting diodes (LEDs). In experiments with cloned plants growing ex vitro in stressful conditions during acclimation, the effects of optical radiation of various spectral combinations from different photosynthetically active radiation (PAR) spectral regions were studied. The data on the plant development and state of the photosynthetic apparatus, features of photosynthetic gas exchange and transpiration, accumulation of photosynthetic pigments, light curves of photosynthesis, and data on growth processes in light modes using combined quasimonochromatic radiation (either mixture of red, green, and blue light or red, far-red, and blue light) with various ratio of the distinct spectral regions were obtained. Photosynthetic apparatus functional activity under different light conditions was studied with chlorophyll fluorescence determination, and plant stress responses to growing under artificial spectral light conditions were characterized. The experiments were accompanied by detailed plant phenotyping at the structural and functional levels. Plant acclimation and photosynthetic improvements in response to added far-red and green light wavelengths to the main red-blue spectrum have been elucidated.

The effect of canopy architecture on the patterning of "windflecks" within a wheat canopy.

Under field conditions, plants are subject to wind-induced movement which creates fluctuations of light intensity and spectral quality reaching the leaves, defined here as windflecks. Within this study, irradiance within two contrasting wheat (Triticum aestivum) canopies during full sun conditions was measured using a spectroradiometer to determine the frequency, duration and magnitude of low- to high-light events plus the spectral composition during wind-induced movement. Similarly, a static canopy was modelled using three-dimensional reconstruction and ray tracing to determine fleck characteristics without the presence of wind. Corresponding architectural traits were measured manually and in silico including plant height, leaf area and angle plus biomechanical properties. Light intensity can differ up to 40% during a windfleck, with changes occurring on a sub-second scale compared to ~5min in canopies not subject to wind. Features such as a shorter height, more erect leaf stature and having an open structure led to an increased frequency and reduced time interval of light flecks in the CMH79A canopy compared to Paragon. This finding illustrates the potential for architectural traits to be selected to improve the canopy light environment and provides the foundation to further explore the links between plant form and function in crop canopies.

Spectral quality as an eliciting agent in the production of phenolic compounds in the callus of Hyptis marrubioides Epling

Hyptis marrubioides Epling is a species of the Brazilian cerrado traditionally used to treat gastrointestinal and cutaneous infections, pain, and cramps. The use of visible and ultraviolet C (UVC) radiation is a promising strategy to optimize the production of the bioactive metabolites. Therefore, the effect of the spectral quality of light on the production of metabolites was evaluated in H. marrubioides callus. The callus was inoculated on MS medium with 50% of the salt concentration containing 2 mg L-1 naphthaleneacetic acid (NAA) and 1 mg L-1 benzylaminopurine (BAP). The callus cultures were exposed for 20 days to the spectral qualities of white light, blue, red, and blue + red as well as to darkness. In addition, the callus cultivated under white light were exposed to UVC on the 21st day for 0, 30, 60, 120, and 240 seconds. The exposure of H. marrubioides callus to blue light negatively affects the synthesis of phenolic compounds. Red light stimulates the synthesis of caffeic acid and luteolin. Darkness was the best condition among those studied because it was associated with the increased accumulation of caffeic acid, chlorogenic acid, rosmarinic acid, and luteolin. The exposure of H. marrubioides callus cultivated under white light to UVC radiation promoted an increase in the synthesis of chlorogenic acid, ferulic acid, rosmarinic acid, and luteolin.

Changes in spectral quality of underwater light alter phytoplankton community composition

AbstractLight is a fundamental resource for phytoplankton. To utilize the available light, most phytoplankton species possess pigments in taxon‐specific combinations and quantities, which in turn result in a specific use of certain wavelengths. This optimizes the light use efficiency, allows for a complementary use of light, and may be an additional driver for community structure. While the effects of light intensity on phytoplankton biomass production and community composition have been intensively studied, here we focused on the effects of specific light spectrum quality (thus light color) on a natural phytoplankton community. In a controlled mesocosm experiment we reduced the supplied wavelength range to its blue, green, or red part of the light spectrum and compared the responses of each treatment to a full spectrum control over 28 d. Highest community growth rates were observed under blue, lowest under red light. Light absorption by the communities showed adaptation toward the supplied wavelength range. Community composition was significantly affected by light quality treatments, driven by Bacillariophyta and Chlorophyta, whereas pigment composition was not. Furthermore, lower species richness but higher evenness occurred when communities were exposed to red light compared to the full spectrum. We expected the response of phytoplankton communities to changes in the light spectrum to be driven by a combination of species sorting and pigment acclimation; however, the effect of species sorting turned out to be stronger. Our study showed that, even if species might acclimate, changes in the available light spectrum affect primary production and phytoplankton community composition.

Assessing the risk of light reduction from natural sediment resuspension events and dredging activities in an inshore turbid reef environment

The reduction in benthic light from natural sediment resuspension events, dredging activities and clouds was quantified over multiple time periods (days to weeks) from a 3-year in-situ field study in the inshore turbid-zone coral communities of the Great Barrier Reef. The results were then used to examine the tolerance levels of three coral species and a sponge to light reduction and associated changes in spectral light quality (in conjunction with elevated sediment concentrations) in a 28-day laboratory-based study. All species survived the exposures but sub-lethal responses involving changes in pigmentation, lipids and lipid ratios were observed. A pocilloporid coral was the most sensitive taxon, with a 28-d EC10 value for bleaching (dissociation of the symbiosis) of 2.7 mol photons m2 d−1. The possibility of such light reduction levels occurring naturally and/or during maintenance dredging activities was then examined using the 3-year in-situ field study as part of a risk assessment.

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.

Better light spectral quality and thermal amplitude inside the greenhouse stimulate growth and improve acclimatization of in vitro–grown Cattleya warneri T. Moore

Growth and photosynthetic capacity of Cattleya warneri T. Moore seedlings cultivated in vitro were evaluated in two environments: (1) growth room (GR) with constant light, humidity, and temperature; and (2) greenhouse (GH) with variable humidity, temperature, and light intensity and quality. In both environments, two different tissue culture vessel lids were used: transparent plastic lids (TCVplastic) and non-transparent metal lids (TCVmetal). After 11 months of in vitro cultivation, five seedlings from each tissue culture vessel were evaluated for growth and photosynthetic capacity, while the other five seedlings of each tissue culture vessel were transferred to a greenhouse for acclimatization. Increased biomass production in vitro was observed in GH and GR (GH>GR). However, the photosynthetic capacity was not altered by the GH environment, since the net photosynthetic rate at 300 μmol m−2 s−1 (NPR300) was low in the final of period in all treatments. Therefore, the increase in biomass production in C. warneri was mostly dependent on the exogenous carbon source through the addition of sucrose to the culture medium. The use of TCVplastic in vitro improved seedlings’ growth in both GR and GH, showing an advantage in relation to TCVmetal. GH environment with quality light spectrum and thermal amplitude, and use of TCVplastic, increased biomass production in vitro and improved the acclimatization process of C. warneri seedlings, which also reduced electricity costs since the use of artificial light and air conditioning is not required.

Photosynthetic apparatus performance of tomato seedlings grown under various combinations of LED illumination.

It is already known that the process of photosynthesis depends on the quality and intensity of light. However, the influence of the new light sources recently used in horticulture, known as Light Emitting Diodes (LEDs), on this process is not yet fully understood. Chlorophyll a fluorescence measurement has been widely used as a rapid, reliable, and noninvasive tool to study the efficiency of the photosystem II (PSII) and to evaluate plant responses to various environmental factors, including light intensity and quality. In this work, we tested the responses of the tomato photosynthetic apparatus to different light spectral qualities. Our results showed that the best performance of the photosynthetic apparatus was observed under a mixture of red and blue light (R7:B3) or a mixture of red, green and blue light (R3:G2:B5). This was demonstrated by the increase in the effective photochemical quantum yield of PSII (Y[II]), photochemical quenching (qP) and electron transport rate (ETR). On the other hand, the mixture of red and blue light with a high proportion of blue light led to an increase in non-photochemical quenching (NPQ). Our results can be used to improve the production of tomato plants under artificial light conditions. However, since we found that the responses of the photosynthetic apparatus of tomato plants to a particular light regime were cultivar-dependent and there was a weak correlation between the growth and photosynthetic parameters tested in this work, special attention should be paid in future research.

Physiological responses of sun choke’s seedlings under different wavelength LED lighting

The impacts of light sources on development, morphological characteristics, and chlorophyll fluorescence of Jerusalem artichoke (Helianthus tuberosus L; JA) seedlings were investigated under natural light (NL), fluorescence light (FL), red light LEDs (R), blue light LEDs (B) and red + blue light LEDs (R + B) (photosynthetic photon flux density 326.74, 30.61, 159.23, 445.38 and 332.56 μmol m−2·s-1, respectively). Morphological appearances of seedlings were significantly different, The R and R + B lighting significantly reduced seedling height and internode length when compare with NL. In contrast, B light could enhance JA seedling growth by increase stem dry weight and net assimilation rate (NAR). Photosynthetic efficiency in terms of photochemical quenching (qP) of seedling were higher under B light than FL light. JA response of seedlings under B light condition was much overall better yield compare to another light source condition. Taken together, R and R + B lighting facilitated plant shortening and more compact canopy, emphasizing the importance of R light spectral quality to manipulate plant growth. It therefore represents modify alternative method to obtain edible potted JA plants under control lighting.

Dissolved organic matter from tropical peatlands reduces shelf sea light availability in the Singapore Strait, Southeast Asia

Shelf seas provide valuable ecosystem services, but their productivity and ecological functioning depend critically on sunlight transmitted through the water column. Anthropogenic reductions in underwater light availability are thus a serious threat to coastal habitats. The flux of light-absorbing coloured dissolved organic matter (CDOM) from land to sea may have increased world-wide, but how this has altered the availability and spectral quality of light in shelf seas remains poorly known. We present time-series data from the Sunda Shelf in Southeast Asia, where the monsoon-driven reversal in ocean currents supplies water enriched in CDOM from tropical peatlands for part of the year, resulting in 5- to 10-fold seasonal variation in light absorption by CDOM. We show that this terrigenous CDOM can dominate underwater light absorption at wavelengths up to 500 nm, and shift the underwater irradiance spectrum towards longer wavelengths. The seasonal presence of terrigenous CDOM also reduces the 10% light penetration depth by 1-5 m, or 10-45%. We estimate that on average 0.6 m, or 25%, of this terrigenous CDOM-mediated shoaling might be attributable to the enhanced input of dissolved organic matter following peatland disturbance. The seasonal change in the light environment is correlated with changes in phytoplankton absorption spectra that suggest a photo-acclimation response, and we infer that terrigenous CDOM likely contributes to limiting the depth distribution of photosynthetic corals. The results reveal an ecologically important but largely overlooked impact of human modifications to carbon fluxes that is likely increasingly important in coastal seas.