Steady-state stomatal responses of C3 and C4 species to blue light fraction: Interactions with CO2 concentration

Tuneable Red and Blue Emission of Bi3+-Co-Doped SrF2:Eu3+ Nanophosphors for LEDs in Agricultural Applications

Tunable blue/red dual-emitting Eu3+-doped, Bi3+-sensitized SrF2 phosphors were synthesized utilizing a solvothermal-microwave method. All phosphors have cubic structure (Fm-3m (225) space group) and well-distinct sphere-like particles with a size of ~20 nm, as examined by X-ray diffraction and transmission electron microscopy. The diffuse reflectance spectra reveal a redshift of the absorption band in the UV region as the Bi3+ concentration in SrF2: Eu3+ phosphor increases. Under the 265 nm excitation, photoluminescence spectra show emission at around 400 nm from the host matrix and characteristic orange 5D0 → 7F1,2 and deep red 5D0 → 7F4 Eu3+ emissions. The red emission intensity increases with an increase in Bi3+ concentration up to 20 mol%, after which it decreases. The integrated intensity of Eu3+ red emission in the representative 20 mol% Bi3+ co-doped SrF2:10 mol% Eu3+ shows twice as bright emission compared to the Bi3+-free sample. To demonstrate the potential application in LEDs for artificial light-based plant factories, the powder with the highest emission intensity, SrF2: 10Eu, 20 Bi, was mixed with a ceramic binder and placed on top of a 275 nm UVC LED chip, showing pinkish violet light corresponding to blue (409 nm) and red (592, 614, and 700 nm) phosphors' emission.

Investigating the influence of varied ratios of red and far-red light on lettuce (Lactuca sativa): effects on growth, photosynthetic characteristics and chlorophyll fluorescence

Far red photon flux accelerates photosynthetic electron transfer rates through photosynthetic pigments, influencing various biological processes. In this study, we investigated the impact of differing red and far-red light ratios on plant growth using LED lamps with different wavelengths and Ca1.8Mg1.2Al2Ge3O12:0.03Cr3+ phosphor materials. The control group (CK) consisted of a plant growth special lamp with 450 nm blue light + 650 nm red light. Four treatments were established: F1 (650 nm red light), F2 (CK + 730 nm far-red light in a 3:2 ratio), F3 (650 nm red light + 730 nm far-red light in a 3:2 ratio), and F4 (CK + phosphor-converted far-red LED in a 3:2 ratio). The study assessed changes in red and far-red light ratios and their impact on the growth morphology, photosynthetic characteristics, fluorescence characteristics, stomatal status, and nutritional quality of cream lettuce. The results revealed that the F3 light treatment exhibited superior growth characteristics and quality compared to the CK treatment. Notably, leaf area, aboveground fresh weight, vitamin C content, and total soluble sugar significantly increased. Additionally, the addition of far-red light resulted in an increase in stomatal density and size, and the F3 treatments were accompanied by increases in net photosynthetic rate (Pn), transpiration rate (Tr), intercellular CO2 concentration (Ci), and stomatal conductance (Gs). The results demonstrated that the F3 treatment, with its optimal red-to-far-red light ratio, promoted plant growth and photosynthetic characteristics. This indicates its suitability for supplementing artificial light sources in plant factories and greenhouses.

Quantifying the Photosynthetic Quantum Yield of Ultraviolet-A1 Radiation

Although it powers photosynthesis, ultraviolet-A1 radiation (UV-A1) is usually not defined as photosynthetically active radiation (PAR). However, the quantum yield (QY) with which UV-A1 drives net photosynthesis rate (A) is unknown, as are the kinetics of A and chlorophyll fluorescence under constant UV-A1 exposure. We measured A in leaves of six genotypes at four spectra peaking at 365, 385, 410 and 450 nm, at intensities spanning 0-300 μmol m s-1. All treatments powered near-linear increases in A in a wavelength-dependent manner. QY at 365 and 385 nm was linked to the apparent concentration of flavonoids, implicating the pigment in reductions of photosynthetic efficiency under UV-A1; in several genotypes, A under 365 and 385 nm was negative regardless of illumination intensity, suggesting very small contributions of UV-A1 radiation to CO2 fixation. Exposure to treatment spectra for 30 min caused slow increases in nonphotochemical quenching, transient reductions in A and dark-adapted maximum quantum yield of photosystem II, that depended on wavelength and intensity, but were generally stronger the lower the peak wavelength was. We conclude that UV-A1 generally powers A, but its definition as PAR requires additional evidence of its capacity to significantly increase whole-canopy carbon uptake in nature.

A guide to photosynthetic gas exchange measurements: Fundamental principles, best practice and potential pitfalls

Gas exchange measurements enable mechanistic insights into the processes that underpin carbon and water fluxes in plant leaves which in turn inform understanding of related processes at a range of scales from individual cells to entire ecosytems. Given the importance of photosynthesis for the global climate discussion it is important to (a) foster a basic understanding of the fundamental principles underpinning the experimental methods used by the broad community, and (b) ensure best practice and correct data interpretation within the research community. In this review, we outline the biochemical and biophysical parameters of photosynthesis that can be investigated with gas exchange measurements and we provide step-by-step guidance on how to reliably measure them. We advise on best practices for using gas exchange equipment and highlight potential pitfalls in experimental design and data interpretation. The Supporting Information contains exemplary data sets, experimental protocols and data-modelling routines. This review is a community effort to equip both the experimental researcher and the data modeller with a solid understanding of the theoretical basis of gas-exchange measurements, the rationale behind different experimental protocols and the approaches to data interpretation.

Supplementary Far-Red Light for Photosynthetic Active Radiation Differentially Influences the Photochemical Efficiency and Biomass Accumulation in Greenhouse-Grown Lettuce

Adding far-red (FR, 700-800 nm) light to photosynthetic active radiation (400-700 nm) proved to be a possible approach to increasing plant biomass accumulation for lettuce production in indoor vertical farms with artificial lighting as a sole-source lighting. However, how FR light addition influences plant growth, development, and metabolic processes and the optimal value of FR photon flux density for greenhouse-grown lettuce under sunlight are still unclear. This work aims to quantify the value of supplementary FR light with different intensities on lettuce morphological and physiological characteristics in a greenhouse. Lettuce 'Dasusheng' (Lactuca sativa L.) was grown in a greenhouse under seven light treatments, including white plus red LEDs with FR photon flux density at 0, 10, 30, 50, 70, and 90 µmol m-2 s-1 (WR, WR + FR10, WR + FR30, WR + FR50, WR + FR70, and WR + FR90, respectively), and lettuce grown with sunlight only was marked as natural light (NL). FR light addition improved the electron transport flux per cross section and performance index (PIabs, PItotal) and decreased the changes in relative variable fluorescence of lettuce leaves compared to plants under NL. Specifically, the PIabs of lettuce leaves were 41%, 41%, 38%, 33%, 26%, and 25% lower under control than in plants under treatments WR + FR90, WR + FR70, WR + FR50, WR + FR30, WR + FR10, and WR, respectively. Leaf number, leaf area, and biomass accumulation of lettuce followed a quadratic function with increasing FR light intensity and were the highest under treatment WR + FR50. The shoot fresh weight and dry weight of lettuce were increased by 111% and 275%, respectively, under treatment WR + FR50 compared to NL. The contents of vitamin C, reducing sugar, total soluble sugar, and starch in lettuce showed a similar trend with biomass accumulation. In conclusion, with commonly used photosynthetic photon flux density (PPFD, 400-700 nm) around 200 μmol m-2 s-1, supplementary FR light intensity of 30~50 μmol m-2 s-1 was suggested to enhance the photochemistry efficiency, biomass accumulation, and carbohydrates' contents in greenhouse-grown lettuce.

Far-red light enrichment affects gene expression and architecture as well as growth and photosynthesis in rice

Plants use light as a resource and signal. Photons within the 400-700 nm waveband are considered photosynthetically active. Far-red photons (FR, 700-800 nm) are used by plants to detect nearby vegetation and elicit the shade avoidance syndrome. In addition, FR photons have also been shown to contribute to photosynthesis, but knowledge about these dual effects remains scarce. Here, we study shoot-architectural and photosynthetic responses to supplemental FR light during the photoperiod in several rice varieties. We observed that FR enrichment only mildly affected the rice transcriptome and shoot architecture as compared to established model species, whereas leaf formation, tillering and biomass accumulation were clearly promoted. Consistent with this growth promotion, we found that CO2-fixation in supplemental FR was strongly enhanced, especially in plants acclimated to FR-enriched conditions as compared to control conditions. This growth promotion dominates the effects of FR photons on shoot development and architecture. When substituting FR enrichment with an end-of-day FR pulse, this prevented photosynthesis-promoting effects and elicited shade avoidance responses. We conclude that FR photons can have a dual role, where effects depend on the environmental context: in addition to being an environmental signal, they are also a potent source of harvestable energy.

Solar Azo-Switches for Effective E→Z Photoisomerization by Sunlight

Natural photoactive systems have evolved to harness broad-spectrum light from solar radiation for critical functions such as light perception and photosynthetic energy conversion. Molecular photoswitches, which undergo structural changes upon light absorption, are artificial photoactive tools widely used for developing photoresponsive systems and converting light energy. However, photoswitches generally need to be activated by light of specific narrow wavelength ranges for effective photoconversion, which limits their ability to directly work under sunlight and to efficiently harvest solar energy. Here, focusing on azo-switches-the most extensively studied photoswitches, we demonstrate effective solar E→Z photoisomerization with photoconversions exceeding 80 % under unfiltered sunlight. These sunlight-driven azo-switches are developed by rendering the absorption of E isomers overwhelmingly stronger than that of Z isomers across a broad ultraviolet to visible spectrum. This unusual type of spectral profile is realized by a simple yet highly adjustable molecular design strategy, enabling the fine-tuning of spectral window that extends light absorption beyond 600 nm. Notably, back-photoconversion can be achieved without impairing the forward solar isomerization, resulting in unique light-reversible solar switches. Such exceptional solar chemistry of photoswitches provides unprecedented opportunities for developing sustainable light-driven systems and efficient solar energy technologies.

Light emitting diode effect of red, blue, and amber light on photosynthesis and plant growth parameters

The visible light spectrum (400-700 nm) powers plant photosynthesis and innumerable other biological processes. Photosynthesis curves plotted by pioneering photobiologists show that amber light (590-620 nm) induces the highest photosynthetic rates in this spectrum. Yet, both red and blue light are viewed superior in their influence over plant growth. Here we report two approaches for quantifying how light wavelength photosynthesis and plant growth using light emitting diodes (LEDs). Resolved quantum yield spectra of tomato and lettuce plants resemble those acquired earlier, showing high quantum utilization efficiencies in the 420-430 nm and 590-620 nm regions. Tomato plants grown under blue (445 nm), amber (595 nm), red (635 nm), and combined red-blue-amber light for 14 days show that amber light yields higher fresh and dry mass, by at least 20%. Principle component analysis shows that amber light has a more pronounced and direct effect on fresh mass, whereas red light has a major effect on dry mass. These data clarify amber light's primary role in photosynthesis and suggest that bandwidth determines plant growth and productivity under sole amber lighting. Findings set precedence for future work aimed at maximizing plant productivity, with widespread implications for controlled environment agriculture.

The role of red and white light in optimizing growth and accumulation of plant specialized metabolites at two light intensities in medical cannabis (Cannabis sativa L.)

The cultivation of medical cannabis (Cannabis sativa L.) is expanding in controlled environments, driven by evolving governmental regulations for healthcare supply. Increasing inflorescence weight and plant specialized metabolite (PSM) concentrations is critical, alongside maintaining product consistency. Medical cannabis is grown under different spectra and photosynthetic photon flux densities (PPFD), the interaction between spectrum and PPFD on inflorescence weight and PSM attracts attention by both industrialists and scientists. Plants were grown in climate-controlled rooms without solar light, where four spectra were applied: two low-white spectra (7B-20G-73R/Narrow and 6B-19G-75R/2Peaks), and two high-white (15B-42G-43R/Narrow and 17B-40G-43R/Broad) spectra. The low-white spectra differed in red wavelength peaks (100% 660 nm, versus 50:50% of 640:660 nm), the high-white spectra differed in spectrum broadness. All four spectra were applied at 600 and 1200 μmol m-2 s-1. Irrespective of PPFD, white light with a dual red peak of 640 and 660 nm (6B-19G-75R/2Peaks) increased inflorescence weight, compared to white light with a single red peak of 660 nm (7B-20G-73R/Narrow) (tested at P = 0.1); this was associated with higher total plant dry matter production and a more open plant architecture, which likely enhanced light capture. At high PPFD, increasing white fraction and spectrum broadness (17B-40G-43R/Broad) produced similar inflorescence weights compared to white light with a dual red peak of 640 and 660 nm (6B-19G-75R/2Peaks). This was caused by an increase of both plant dry matter production and dry matter partitioning to the inflorescences. No spectrum or PPFD effects on cannabinoid concentrations were observed, although at high PPFD white light with a dual red peak of 640 and 660 nm (6B-19G-75R/2Peaks) increased terpenoid concentrations compared to the other spectra. At low PPFD, the combination of white light with 640 and 660 nm increased photosynthetic efficiency compared with white light with a single red peak of 660nm, indicating potential benefits in light use efficiency and promoting plant dry matter production. These results indicate that the interaction between spectrum and PPFD influences plant dry matter production. Dividing the light energy in the red waveband over both 640 and 660 nm equally shows potential in enhancing photosynthesis and plant dry matter production.

Far-red light increases maize volatile emissions in response to volatile cues from neighbouring plants

Plants perceive the presence and defence status of their neighbours through light and volatile cues, but how plants integrate both stimuli is poorly understood. We investigated if and how low Red to Far red light (R:FR) ratios, indicative of shading or canopy closure, affect maize (Zea mays) responses to herbivore-induced plant volatiles (HIPVs), including the green leaf volatile (Z)-3-hexenyl acetate. We modulated light signalling and perception by using FR supplementation and a phyB1phyB2 mutant, and we determined volatile release as a response readout. To gain mechanistic insights, we examined expression of volatile biosynthesis genes, hormone accumulation, and photosynthesis. Exposure to a full blend of HIPVs or (Z)-3-hexenyl acetate induced maize volatile release. Short-term FR supplementation increased this response. In contrast, prolonged FR supplementation or constitutive phytochrome B inactivation in phyB1phyB2 plants showed the opposite response. Short-term FR supplementation enhanced photosynthesis and stomatal conductance and (Z)-3-hexenyl acetate-induced JA-Ile levels. We conclude that a FR-enriched light environment can prompt maize plants to respond more strongly to HIPVs emitted by neighbours, which might be explained by changes in photosynthetic processes and phytochrome B signalling. Our findings reveal interactive responses to light and volatile cues with potentially important consequences for plant-plant and plant-herbivore interactions.

Transcriptomic Insights into Molecular Response of Butter Lettuce to Different Light Wavelengths

Lettuce is a widely consumed leafy vegetable; it became popular due to its enhanced nutritional content. Recently, lettuce is also regarded as one of the model plants for vegetable production in plant factories. Light and nutrients are essential environmental factors that affect lettuce growth and morphology. To evaluate the impact of light spectra on lettuce, butter lettuce was grown under the light wavelengths of 460, 525, and 660 nm, along with white light as the control. Plant morphology, physiology, nutritional content, and transcriptomic analyses were performed to study the light response mechanisms. The results showed that the leaf fresh weight and length/width were higher when grown at 460 nm and lower when grown at 525 nm compared to the control treatment. When exposed to 460 nm light, the sugar, crude fiber, mineral, and vitamin concentrations were favorably altered; however, these levels decreased when exposed to light with a wavelength of 525 nm. The transcriptomic analysis showed that co-factor and vitamin metabolism- and secondary metabolism-related genes were specifically induced by 460 nm light exposure. Furthermore, the pathway enrichment analysis found that flavonoid biosynthesis- and vitamin B6 metabolism-related genes were significantly upregulated in response to 460 nm light exposure. Additional experiments demonstrated that the vitamin B6 and B2 content was significantly higher in leaves exposed to 460 nm light than those grown under the other conditions. Our findings suggested that the addition of 460 nm light could improve lettuce's biomass and nutritional value and help us to further understand how the light spectrum can be tuned as needed for lettuce production.

Tomato and mini-cucumber tolerance to photoperiodic injury involves photorespiration and the engagement of nighttime cyclic electron flow from dynamic LEDs

Controlled environment agriculture (CEA) is critical for achieving year-round food security in many regions of the world. CEA is a resource-intensive endeavor, with lighting consuming a large fraction of the energy. To lessen the burden on the grid and save costs, an extended photoperiod strategy can take advantage of off-peak time-of-day options from utility suppliers. However, extending the photoperiod limits crop production morphologically and physiologically if pushed too long. Here, we present a continuous-light dynamic light-emitting diode (LED) strategy (involving changes in spectra, intensity, and timing), that overcomes these limitations. We focused on tomato, a well described photoperiodic injury-sensitive species, and mini-cucumber, a photoperiodic injury-tolerant species to first assess morphological responses under control (16-h photoperiod, unchanging spectrum), constant (24-h photoperiod, unchanging spectrum), and two variations of a dynamic LED strategy, dynamic 1 (16-h "day", 3-h "peak", 8-h "night" spectra) and dynamic 2 (20-h "day", 5-h "peak", 4-h "night" spectra). Next, we tested the hypothesis of photorespiration's involvement in photoperiodic injury by using a leaf gas exchange coupled with chlorophyll fluorescence protocol. We further explored Adenosine triphosphate (ATP): Nicotinamide adenine dinucleotide phosphate (NADPH) ratio supply/demand responses by probing photosynthetic electron flow and proton flow with the MultispeQ instrument. We found canopy architecture can be tuned by minor variations of the same dynamic LED strategy, and we highlight dynamic 1 as the optimal choice for both tomato and mini-cucumber as it improved biomass/architecture and first-yield, respectively. A central discovery was that dynamic 1 had a significantly higher level of photorespiration than control, for both species. Unexpectedly, photorespiration was comparable between species under the same treatments, except under constant. However, preliminary data on a fully tolerant tomato genotype grown under constant treatment upregulated photorespiration similar to mini-cucumber. These results suggest that photoperiodic injury tolerance involves a sustained higher level of photorespiration under extended photoperiods. Interestingly, diurnal MultispeQ measurements point to the importance of cyclic electron flow at subjective nighttime that may also partially explain why dynamic LED strategies mitigate photoperiodic injury. We propose an ontology of photoperiodic injury involving photorespiration, triose phosphate utilization, peroxisomal H2O2-catalase balance, and a circadian external coincidence model of sensitivity that initiates programmed cell death.

Beyond the visible: Accounting for ultraviolet and far-red radiation in vegetation productivity and surface energy budgets

Photosynthetically active radiation (PAR) is typically defined as light with a wavelength within 400-700 nm. However, ultra-violet (UV) radiation within 280-400 nm and far-red (FR) radiation within 700-750 nm can also excite photosystems, though not as efficiently as PAR. Vegetation and land surface models (LSMs) typically do not explicitly account for UV's contribution to energy budgets or photosynthesis, nor FR's contribution to photosynthesis. However, whether neglecting UV and FR has significant impacts remains unknown. We explored how canopy radiative transfer (RT) and photosynthesis are impacted when explicitly implementing UV in the canopy RT model and accounting for UV and FR in the photosynthesis models within a next-generation LSM that can simulate hyperspectral canopy RT. We validated our improvements using photosynthesis measurements from plants under different light sources and intensities and surface reflection from an eddy-covariance tower. Our model simulations suggested that at the whole plant level, after accounting for UV and FR explicitly, chlorophyll content, leaf area index (LAI), clumping index, and solar radiation all impact the modeling of gross primary productivity (GPP). At the global scale, mean annual GPP within a grid would increase by up to 7.3% and the increase is proportional to LAI; globally integrated GPP increases by 4.6 PgC year-1 (3.8% of the GPP without accounting for UV + FR). Further, using PAR to proxy UV could overestimate surface albedo by more than 0.1, particularly in the boreal forests. Our results highlight the importance of improving UV and FR in canopy RT and photosynthesis modeling and the necessity to implement hyperspectral or multispectral canopy RT schemes in future vegetation and LSMs.

Effect of Far-Red Light on Biomass Accumulation, Plant Morphology, and Phytonutrient Composition of Ruby Streaks Mustard at Microgreen, Baby Leaf, and Flowering Stages

Far-red (FR) light influences plant development significantly through shade avoidance response and photosynthetic modulation, but there is limited knowledge on how FR treatments influence the growth and nutrition of vegetables at different maturity stages in controlled environment agriculture (CEA). Here, we comprehensively investigated the impacts of FR on the yield, morphology, and phytonutrients of ruby streaks mustard (RS) at microgreen, baby leaf, and flowering stages. Treatments including white control, white with supplementary FR, white followed by singularly applied FR, and enhanced white (WE) matching the extended daily light integral (eDLI) of FR were designed for separating the effects of light intensity and quality. Results showed that singular and supplemental FR affected plant development and nutrition similarly throughout the growth cycle, with light intensity and quality playing varying roles at different stages. Specifically, FR did not affect the fresh and dry weight of microgreens but increased those values for baby leaves, although not as effectively as WE. Meanwhile, FR caused significant morphological change and accelerated the development of leaves, flowers, and seedpods more dramatically than WE. With regard to phytonutrients, light treatments affected the metabolomic profiles for baby leaves more dramatically than microgreens and flowers. FR decreased the glucosinolate and anthocyanin contents in microgreens and baby leaves, while WE increased the contents of those compounds in baby leaves. This study illustrates the complex impacts of FR on RS and provides valuable information for selecting optimal lighting conditions in CEA.

Physiological adaptation to irradiance in duckweeds is species and accession specific and depends on light habitat niche

Duckweeds span 36 species of free-floating aquatic organisms with body sizes ranging from 2 mm to 10 mm, where each plant body plan is reduced to a largely leaf-like structure. As an emerging crop, their fast growth rates offer potential for cultivation in closed systems. We describe a novel UK collection derived from low light (dLL) or high light (dHL) habitats, profiled for growth, photosynthesis, and photoprotection (non-photochemical quenching, NPQ) responses. Twenty-three accessions of three Lemna species and one Spirodela polyrhiza were grown under relatively low light (LL: 100 μmol m-2 s-1) and high light (HL: 350 μmol m-2 s-1) intensities. We observed broad within- and between-species level variation in photosynthesis acclimation. Duckweeds grown under HL exhibited a lower growth rate, biomass, chlorophyll, and quantum yield of photosynthesis. In HL compared with LL, carotenoid de-epoxidation state and NPQ were higher, whilst PSII efficiency (φPSII) and Chl a:b ratios were unchanged. The dLL plants showed relatively stronger acclimation to HL compared with dHL plants, especially Lemna japonica accessions. These achieved faster growth in HL with concurrent higher carotenoid levels and NPQ, and less degradation of chlorophyll. We conclude that these data support local adaptation to the light environment in duckweed affecting acclimation in controlled conditions.

Far-red light modulates grapevine growth by increasing leaf photosynthesis efficiency and triggering organ-specific transcriptome remodelling : Author

BACKGROUND

Growing evidence demonstrates that the synergistic interaction of far-red light with shorter wavelength lights could evidently improve the photosynthesis efficiency of multiple species. However, whether/how far-red light affects sink organs and consequently modulates the source‒sink relationships are largely unknown.

RESULTS

Here, equal intensities of white and far-red lights were added to natural light for grape plantlets to investigate the effects of far-red light supplementation on grapevine growth and carbon assimilate allocation, as well as to reveal the underlying mechanisms, through physiological and transcriptomic analysis. The results showed that additional far-red light increased stem length and carbohydrate contents in multiple organs and decreased leaf area, specific leaf weight and dry weight of leaves in comparison with their counterparts grown under white light. Compared to white light, the maximum net photosynthetic rate of the leaves was increased by 31.72% by far-red light supplementation, indicating that far-red light indeed elevated the photosynthesis efficiency of grapes. Transcriptome analysis revealed that leaves were most responsive to far-red light, followed by sink organs, including stems and roots. Genes related to light signaling and carbon metabolites were tightly correlated with variations in the aforementioned physiological traits. In particular, VvLHCB1 is involved in light harvesting and restoring the balance of photosystem I and photosystem II excitation, and VvCOP1 and VvPIF3, which regulate light signal transduction, were upregulated under far-red conditions. In addition, the transcript abundances of the sugar transporter-encoding genes VvSWEET1 and VvSWEET3 and the carbon metabolite-encoding genes VvG6PD, VvSUS7 and VvPGAM varied in line with the change in sugar content.

CONCLUSIONS

This study showed that far-red light synergistically functioning with white light has a beneficial effect on grape photosystem activity and is able to differentially affect the growth of sink organs, providing evidence for the possible addition of far-red light to the wavelength range of photosynthetically active radiation (PAR).

The crosstalk of far-red energy and signaling defines the regulation of photosynthesis, growth, and flowering in tomatoes

This study investigated the effect of light intensity and signaling on the regulation of far-red (FR)-induced alteration in photosynthesis. The low (LL: 440 μmol m-2 s-1) and high (HL: 1135 μmol m-2 s-1) intensity of white light with or without FR (LLFR: 545 μmol m-2 s-1 including 115 μmol m-2 s-1; HLFR: 1254 μmol m-2 s-1 + 140 μmol m-2 s-1) was applied on the tomato cultivar (Solanum Lycopersicon cv. Moneymaker) and mutants of phytochrome A (phyA) and phytochrome B (phyB1, and phyB2). Both light intensity and FR affected plant morphological traits, leaf biomass, and flowering time. Irrespective of genotype, flowering was delayed by LLFR and accelerated by HLFR compared to the corresponding light intensity without FR. In LLFR, a reduced energy flux through the electron transfer chain along with a reduced energy dissipation per reaction center improved the maximum quantum yield of PSII, irrespective of genotype. HLFR increased net photosynthesis and gas exchange properties in a genotype-dependent manner. FR-dependent regulation of hormones was affected by light signaling. It appeared that PHYB affected the levels of abscisic acid and salicylic acid while PHYA took part in the regulation of CK in FR-exposed plants. Overall, light intensity and signaling of FR influenced plants' photosynthesis and growth by altering electron transport, gas exchange, and changes in the level of endogenous hormones.

Supplementary Low Far-Red Light Promotes Proliferation and Photosynthetic Capacity of Blueberry In Vitro Plantlets

Far-red light exerts an important regulatory influence on plant growth and development. However, the mechanisms underlying far-red light regulation of morphogenesis and photosynthetic characteristics in blueberry plantlets in vitro have remained elusive. Here, physiological and transcriptomic analyses were conducted on blueberry plantlets in vitro supplemented with far-red light. The results indicated that supplementation with low far-red light, such as 6 μmol m-2 s-1 and 14 μmol m-2 s-1 far-red (6FR and 14FR) light treatments, significantly increased proliferation-related indicators, including shoot length, shoot number, gibberellin A3, and trans-zeatin riboside content. It was found that 6FR and 14 FR significantly reduced chlorophyll content in blueberry plantlets but enhanced electron transport rates. Weighted correlation network analysis (WGCNA) showed the enrichment of iron ion-related genes in modules associated with photosynthesis. Genes such as NAC, ABCG11, GASA1, and Erf74 were significantly enriched within the proliferation-related module. Taken together, we conclude that low far-red light can promote the proliferative capacity of blueberry plantlets in vitro by affecting hormone pathways and the formation of secondary cell walls, concurrently regulating chlorophyll content and iron ion homeostasis to affect photosynthetic capacity.

The Effects of Light Spectrum and Intensity, Seeding Density, and Fertilization on Biomass, Morphology, and Resource Use Efficiency in Three Species of Brassicaceae Microgreens

Light is a critical component of indoor plant cultivation, as different wavelengths can influence both the physiology and morphology of plants. Furthermore, fertilization and seeding density can also potentially interact with the light recipe to affect production outcomes. However, maximizing production is an ongoing research topic, and it is often divested from resource use efficiencies. In this study, three species of microgreens-kohlrabi; mustard; and radish-were grown under five light recipes; with and without fertilizer; and at two seeding densities. We found that the different light recipes had significant effects on biomass accumulation. More specifically, we found that Far-Red light was significantly positively associated with biomass accumulation, as well as improvements in height, leaf area, and leaf weight. We also found a less strong but positive correlation with increasing amounts of Green light and biomass. Red light was negatively associated with biomass accumulation, and Blue light showed a concave downward response. We found that fertilizer improved biomass by a factor of 1.60 across species and that using a high seeding density was 37% more spatially productive. Overall, we found that it was primarily the main effects that explained microgreen production variation, and there were very few instances of significant interactions between light recipe, fertilization, and seeding density. To contextualize the cost of producing these microgreens, we also measured resource use efficiencies and found that the cheaper 24-volt LEDs at a high seeding density with fertilizer were the most efficient production environment for biomass. Therefore, this study has shown that, even with a short growing period of only four days, there was a significant influence of light recipe, fertilization, and seeding density that can change morphology, biomass accumulation, and resource input costs.

Spectral Reflectance Measurements

This chapter provides a methodology for evaluating plant health and leaf characteristics using spectral reflectance. It provides a step-by-step guide to using spectrometers for high-resolution point measurements of leaf spectral reflectance and multispectral imaging for capturing spatial data, emphasizing the importance of consistent measurement conditions. The chapter further explores the intricacies of multispectral imaging, including calibration, data collection, and image processing. Finally, this chapter delves into the application of various spectral indices for the quantification of key traits such as pigment content, the status of the xanthophyll cycle, water content, and how to identify spectral regions of interest for further research and development. Serving as a guide for researchers and practitioners in plant science, this chapter provides a straightforward framework for plant health assessment using spectral reflectance.

Biochemical repercussions of light spectra on nitrogen metabolism in spinach (Spinacia oleracea) under a controlled environment

Introduction

Selecting appropriate light spectra of light-emitting diodes (LEDs) and optimal nutrient composition fertilizers has become integral to commercial controlled environment agriculture (CEA) platforms.

Methods

This study explored the impact of three LED light regimes (BR: Blue17%, Green 4%, Red 63%, Far-Red 13% and infrared 3%, BGR; Blue 20%, Green 23%, Red 47%, Far-Red 8% and infrared 2%; and GR; Blue 25%, Green 41%, Red 32%, and Far-Red 2%) and nitrogen levels (3.6 and 14.3 mM N) on spinach (Spinacea oleracea).

Results

Under limited nitrogen (3.6 mM), BGR light increased the fresh shoot (32%) and root (39%) biomass than BR, suggesting additional green light's impact on assimilating photosynthates under suboptimal nitrogen availability. Reduced chlorophyll (a and b) and carotenoid accumulation, electron transport rate (ETR), and higher oxalates under limited nitrogen availability highlighted the adverse effects of red light (BR) on spinach productivity. Increased activities of nitrogen-associated enzymes (GOGAT; Glutamate synthase, GDH; NADH-Glutamate dehydrogenase, NR; Nitrate reductase, and GS; Glutamine synthetase) in spinach plants under BGR light further validated the significance of green light in nitrogen assimilation. Amino acid distributions remained unchanged across the light spectra, although limited nitrogen availability significantly decreased the percent distribution of glutamine and aspartic acid.

Conclusion

Overall, this study demonstrated the favorable impacts of additional green light on spinach productivity, as demonstrated under BGR, than GR alone in response to nitrogen perturbation. However, the exact mechanisms underlying these impacts still need to be unveiled. Nevertheless, these outcomes provided new insights into our understanding of light spectra on spinach nitrogen metabolism.

Light blocking film in a glasshouse impacts Capsicum annuum L. yield differentially across planting season

High energy costs are a barrier to producing high-quality produce at protected cropping facilities. A potential solution to mitigate high energy costs is film technology, which blocks heat-producing radiation; however, the alteration of the light environment by these films may impact crop yield and quality. Previous studies have assessed the impact of ULR 80 [i.e., light-blocking film (LBF)] on crop yield and photosynthetically active radiation (PAR); however, an assessment of the spectral environment over different seasons is important to understand potential crop impacts through different developmental phases. In this study, two varieties (red and orange) of Capsicum annuum were grown across two crop cycles: one cycle with primary crop growth in the autumn (i.e., autumn experiment [AE]) and the other with primary crop growth in the summer (i.e., summer experiment [SE]). LBF reduced PAR (roof level: 26%-30%, plant canopy level: 8%-25%) and net radiation (36%-66%). LBF also reduced total diffuse PAR (AE: 8%, SE: 15%), but the diffuse fraction of PAR increased by 7% and 9% for AE and SE, respectively, potentially resulting in differential light penetration throughout the canopy across treatments. LBF reduced near-infrared radiation (700 nm-2,500 nm), including far-red (700 nm-780 nm) at mid- and lower-canopy levels. LBF significantly altered light quantity and quality, which determined the amount of time that the crop grew under light-limited (<12 mol m-2 d-1) versus sufficient light conditions. In AE, crops were established and grown under light-limited conditions for 57% of the growing season, whereas in SE, crops were established and grown under sufficient light conditions for 66% of the growing season. Overall, LBF significantly reduced the yield in SE for both varieties (red: 29%; orange: 16%), but not in AE. The light changes in different seasons in response to LBF suggest that planting time is crucial for maximizing fruit yield when grown under a film that reduces light quantity. LBF may be unsuitable for year-round production of capsicum, and additional development of LBF is required for the film to be beneficial for saving energy during production and sustaining good crop yields in protected cropping.

Reaction Center Excitation in Photosystem II: From Multiscale Modeling to Functional Principles

Oxygenic photosynthesis is the fundamental energy-converting process that utilizes sunlight to generate molecular oxygen and the organic compounds that sustain life. Protein-pigment complexes harvest light and transfer excitation energy to specialized pigment assemblies, reaction centers (RC), where electron transfer cascades are initiated. A molecular-level understanding of the primary events is indispensable for elucidating the principles of natural photosynthesis and enabling development of bioinspired technologies. The primary enzyme in oxygenic photosynthesis is Photosystem II (PSII), a membrane-embedded multisubunit complex, that catalyzes the light-driven oxidation of water. The RC of PSII consists of four chlorophyll a and two pheophytin a pigments symmetrically arranged along two core polypeptides; only one branch participates in electron transfer. Despite decades of research, fundamental questions remain, including the origin of this functional asymmetry, the nature of primary charge-transfer states and the identity of the initial electron donor, the origin of the capability of PSII to enact charge separation with far-red photons, i.e., beyond the "red limit" where individual chlorophylls absorb, and the role of protein conformational dynamics in modulating charge-separation pathways.In this Account, we highlight developments in quantum-chemistry based excited-state computations for multipigment assemblies and the refinement of protocols for computing protein-induced electrochromic shifts and charge-transfer excitations calibrated with modern local correlation coupled cluster methods. We emphasize the importance of multiscale atomistic quantum-mechanics/molecular-mechanics and large-scale molecular dynamics simulations, which enabled direct and accurate modeling of primary processes in RC excitation at the quantum mechanical level.Our findings show how differential protein electrostatics enable spectral tuning of RC pigments and generate functional asymmetry in PSII. A chlorophyll pigment on the active branch (ChlD1) has the lowest site energy in PSII and is the primary electron donor. The complete absence of low-lying charge-transfer states within the central pair of chlorophylls excludes a long-held assumption about the initial charge separation. Instead, we identify two primary charge separation pathways, both with the same pheophytin acceptor (PheoD1): a fast pathway with ChlD1 as the primary electron donor (short-range charge-separation) and a slow pathway with PD1PD2 as the initial donor (long-range charge separation). The low-energy spectrum is dominated by two states with significant charge-transfer character, ChlD1δ+PheoD1δ- and PD1δ+PheoD1δ-. The conformational dynamics of PSII allows these charge-transfer states to span wide energy ranges, pushing oxygenic photosynthesis beyond the "red limit". These results provide a quantum mechanical picture of the primary events in the RC of oxygenic photosynthesis, forming a solid basis for interpreting experimental observations and for extending photosynthesis research in new directions.

Crop/Plant Modeling Supports Plant Breeding: I. Optimization of Environmental Factors in Accelerating Crop Growth and Development for Speed Breeding

The environmental conditions in customered speed breeding practice are, to some extent, empirical and, thus, can be further optimized. Crop and plant models have been developed as powerful tools in predicting growth and development under various environments for extensive crop species. To improve speed breeding, crop models can be used to predict the phenotypes resulted from genotype by environment by management at the population level, while plant models can be used to examine 3-dimensional plant architectural development by microenvironments at the organ level. By justifying the simulations via numerous virtual trials using models in testing genotype × environment × management, an optimized combination of environmental factors in achieving desired plant phenotypes can be quickly determined. Artificial intelligence in assisting for optimization is also discussed. We admit that the appropriate modifications on modeling algorithms or adding new modules may be necessary in optimizing speed breeding for specific uses. Overall, this review demonstrates that crop and plant models are promising tools in providing the optimized combinations of environment factors in advancing crop growth and development for speed breeding.

Compensation of adverse growing media effects on plant growth and morphology by supplemental LED lighting

There is an increasing interest in alternatives to peat in growing media due to environmental constraints. However, plants grown in peat substitutes often show impaired growth compared to plants grown in peat-based media. Hence, it would be interesting to know whether these deficiencies can be compensated by supplementing other growth factors, e.g. light. The present study aims to investigate the interactive nature between growing media and supplemental lighting on plant growth and morphology, and to examine whether supplemental light emitting diode (LED) lighting may compensate adverse growing media effects. Basil (Ocimum basilicum L.) and Chinese cabbage (Brassica rapa subsp. pekinensis) were grown in different growing media consisting of peat, green compost, coconut pulp, wood fibre, perlite and sphagnum moss under blue, red and far-red supplemental LED lighting. We found significant interactions between growing media and supplemental photosynthetically active radiation (PAR) on plant growth, morphology and development. At low light intensities, peat-based and substituted growing media performed similarly, whereas with increasing light intensities the peat-based growing media significantly outperformed their alternatives. The substrate choice determines the required amount of supplemental light to compensate for adverse growing media effects and the amount varies depending on plant species and season. Thereby, it was indicated that red light alleviates adverse growing media effects best. We also found that far-red light is not effective when background PAR is low and becomes more effective under high background PAR. The implications and prospects of the results are discussed.

Supplementary White, UV-A, and Far-Red Radiation Differentially Regulates Growth and Nutritional Qualities of Greenhouse Lettuce

Light is a crucial environmental signal and a form of photosynthetic energy for plant growth, development, and nutrient formation. To explore the effects of light quality on the growth and nutritional qualities of greenhouse-grown lettuce (Lactuca sativa L.), lettuce was cultivated under supplementary white (W) light-emitting diodes (LEDs); white plus ultraviolet A LEDs (W+UV); white plus far-red LEDs (W+FR); and the combination of white, far-red, and UV-A LEDs (W+FR+UV) for 25 days, with lettuce grown under natural sunlight used as the control. The results indicate that the leaf length and leaf width values for lettuce grown under the W+FR+UV treatment were significantly higher than those of lettuce grown under other supplementary light treatments. The highest values of shoot fresh weight, shoot dry weight, root fresh weight, and root dry weight were recorded under the W+FR treatment (4.0, 6.0, 8.0, and 12.4 times higher than those under the control treatment, respectively). Lettuce grown under the W+FR treatment exhibited the highest total chlorophyll content (39.1%, 24.6%, and 16.2% higher than that under the W, W+UV, and W+FR+UV treatments, respectively). The carotenoid content of lettuce grown under the W+FR treatment was the highest among all treatments. However, the root activity of greenhouse-grown lettuce was the highest under the W+FR+UV treatment. Soluble sugar content, cellulose content, and starch content in the lettuce responded differently to the light treatments and were highest under the W+UV treatment. In summary, supplementary light promoted growth and nutrient accumulation in lettuce. Specifically, white plus far-red light promoted lettuce growth, and white plus UV increased some specific compounds in greenhouse-grown lettuce. Our findings provide valuable references for the application of light-supplementation strategies to greenhouse lettuce production.

Leaf morphology, optical characteristics and phytochemical traits of butterhead lettuce affected by increasing the far-red photon flux

Light and its spectral characteristics are crucial for plant growth and development. The far-red photon flux mediates many plant processes through the action of phytochrome and also accelerates the photosynthetic electron transfer rate. In this study, we assessed the effects of far-red addition on butterhead lettuce morphology, light use efficiency, optical properties, and phytochemical characteristics. Three-week-old lettuce plants (Lactuca sativa L. cv. Alyssa) were grown for up to 28 days under a 10% blue and 90% red light spectrum (200 µmol m-2 s-1, 16 h photoperiod) to which five different intensities of far-red light (peak at 735 nm) were added (0-9-18-36-72 µmol m-2 s-1). White light-emitting diodes were included as a proxy for sunlight. Increasing supplemental far-red photon flux from zero to 21% increased the light use efficiency (g per mol) by 37% on day 14; 43% on day 21; and 39% on day 28. Measurements of projected head area suggest that this was associated with an increase in leaf expansion and photon capture and not necessarily a direct effect on photosynthesis. Moreover, vegetation indices based on leaf reflectance showed a decrease in chlorophyll-related indices under a high far-red photon flux. This decrease in pigment content was confirmed by chemical analyses, suggesting that the plants may not reach their full potential in terms of photon capture, limiting the overall photosynthetic performance. Furthermore, the stress-related Carter 1 index increased in plants grown under a high far-red photon flux, indicating early plant stress. Far-red tended to decrease the content of total phenolics and increase soluble sugars. The higher sugar levels can be attributed to an improved photochemical efficiency due to photosystem I excitation by far-red wavelengths, also known as the Emerson Enhancement effect. Despite these higher sugar levels, no effect on foliar nitrate content was observed. Our results show that far-red supplementation has the potential to enhance light interception at the early growth stages, although higher intensities of far-red may cause plant stress.

Growth and Photosynthetic Efficiency of Microalgae and Plants with Different Levels of Complexity Exposed to a Simulated M-Dwarf Starlight

Oxygenic photosynthetic organisms (OPOs) are primary producers on Earth and generate surface and atmospheric biosignatures, making them ideal targets to search for life from remote on Earth-like exoplanets orbiting stars different from the Sun, such as M-dwarfs. These stars emit very low light in the visible and most light in the far-red, an issue for OPOs, which mostly utilize visible light to photosynthesize and grow. After successfully testing procaryotic OPOs (cyanobacteria) under a simulated M-dwarf star spectrum (M7, 365-850 nm) generated through a custom-made lamp, we tested several eukaryotic OPOs: microalgae (Dixoniella giordanoi, Microchloropsis gaditana, Chromera velia, Chlorella vulgaris), a non-vascular plant (Physcomitrium patens), and a vascular plant (Arabidopsis thaliana). We assessed their growth and photosynthetic efficiency under three light conditions: M7, solar (SOL) simulated spectra, and far-red light (FR). Microalgae grew similarly in SOL and M7, while the moss P. patens showed slower growth in M7 with respect to SOL. A. thaliana grew similarly in SOL and M7, showing traits typical of shade-avoidance syndrome. Overall, the synergistic effect of visible and far-red light, also known as the Emerson enhancing effect, could explain the growth in M7 for all organisms. These results lead to reconsidering the possibility and capability of the growth of OPOs and are promising for finding biosignatures on exoplanets orbiting the habitable zone of distant stars.

Variation in supplemental lighting quality influences key aroma volatiles in hydroponically grown 'Italian Large Leaf' basil

The spectral quality of supplemental greenhouse lighting can directly influence aroma volatiles and secondary metabolic resource allocation (i.e., specific compounds and classes of compounds). Research is needed to determine species-specific secondary metabolic responses to supplemental lighting (SL) sources with an emphasis on variations in spectral quality. The primary objective of this experiment was to determine the impact of supplemental narrowband blue (B) and red (R) LED lighting ratios and discrete wavelengths on flavor volatiles in hydroponic basil (Ocimum basilicum var. Italian Large Leaf). A natural light (NL) control and different broadband lighting sources were also evaluated to establish the impact of adding discrete and broadband supplements to the ambient solar spectrum. Each SL treatment provided 8.64 mol^.m^-2.d^-1 (100 µmol^.m^-2.s^-1, 24 h^.d^-1) photon flux. The daily light integral (DLI) of the NL control averaged 11.75 mol^.m^-2.d^-1 during the growth period (ranging from 4 to 20 mol^.m^-2.d^-1). Basil plants were harvested 45 d after seeding. Using GC-MS, we explored, identified, and quantified several important volatile organic compounds (VOCs) with known influence on sensory perception and/or plant physiological processes of sweet basil. We found that the spectral quality from SL sources, in addition to changes in the spectra and DLI of ambient sunlight across growing seasons, directly influence basil aroma volatile concentrations. Further, we found that specific ratios of narrowband B/R wavelengths, combinations of discrete narrowband wavelengths, and broadband wavelengths directly and differentially influence the overall aroma profile as well as specific compounds. Based on the results of this study, we recommend supplemental 450 and 660 nm (± 20 nm) wavelengths at a ratio of approximately 10B/90R at 100-200 µmol^.m^-2.s^-1, 12-24 h^.d^-1 for sweet basil grown under standard greenhouse conditions, with direct consideration of the natural solar spectrum and DLI provided for any given location and growing season. This experiment demonstrates the ability to use discrete narrowband wavelengths to augment the natural solar spectrum to provide an optimal light environment across variable growing seasons. Future experiments should investigate SL spectral quality for the optimization of sensory compounds in other high-value specialty crops.

On the contrasting morphological response to far-red at high and low photon fluxes

Plants compete for sunlight and have evolved to perceive shade through both relative increases in the flux of far-red photons (FR; 700 to 750 nm) and decreases in the flux of all photons (intensity). These two signals interact to control stem elongation and leaf expansion. Although the interacting effects on stem elongation are well quantified, responses for leaf expansion are poorly characterized. Here we report a significant interaction between far-red fraction and total photon flux. Extended photosynthetic photon flux density (ePPFD; 400 to 750 nm) was maintained at three levels (50/100, 200 and 500 µmol m^-2 s^-1), each with a range of 2 to 33% FR. Increasing FR increased leaf expansion in three cultivars of lettuce at the highest ePPFD but decreased expansion at the lowest ePPFD. This interaction was attributed to differences in biomass partitioning between leaves and stems. Increased FR favored stem elongation and biomass partitioning to stems at low ePPFD and favored leaf expansion at high ePPFD. In cucumber, leaf expansion was increased with increasing percent FR under all ePPFD levels showing minimal interaction. The interactions (and lack thereof) have important implications for horticulture and warrant further study for plant ecology.

Far-Red Light Mediated Carbohydrate Concentration Changes in Leaves of Sweet Basil, a Stachyose Translocating Plant

Photosynthetic active radiation (PAR) refers to photons between 400 and 700 nm. These photons drive photosynthesis, providing carbohydrates for plant metabolism and development. Far-red radiation (FR, 701-750 nm) is excluded in this definition because no FR is absorbed by the plant photosynthetic pigments. However, including FR in the light spectrum provides substantial benefits for biomass production and resource-use efficiency. We investigated the effects of continuous FR addition and end-of-day additional FR to a broad white light spectrum (BW) on carbohydrate concentrations in the top and bottom leaves of sweet basil (Ocimum basilicum L.), a species that produces the raffinose family oligosaccharides raffinose and stachyose and preferentially uses the latter as transport sugar. Glucose, fructose, sucrose, raffinose, and starch concentrations increased significantly in top and bottom leaves with the addition of FR light. The increased carbohydrate pools under FR light treatments are associated with more efficient stachyose production and potentially improved phloem loading through increased sucrose homeostasis in intermediary cells. The combination of a high biomass yield, increased resource-use efficiency, and increased carbohydrate concentration in leaves in response to the addition of FR light offers opportunities for commercial plant production in controlled growth environments.

A Novel Method for Estimating Chlorophyll and Carotenoid Concentrations in Leaves: A Two Hyperspectral Sensor Approach

Leaf optical properties can be used to identify environmental conditions, the effect of light intensities, plant hormone levels, pigment concentrations, and cellular structures. However, the reflectance factors can affect the accuracy of predictions for chlorophyll and carotenoid concentrations. In this study, we tested the hypothesis that technology using two hyperspectral sensors for both reflectance and absorbance data would result in more accurate predictions of absorbance spectra. Our findings indicated that the green/yellow regions (500-600 nm) had a greater impact on photosynthetic pigment predictions, while the blue (440-485 nm) and red (626-700 nm) regions had a minor impact. Strong correlations were found between absorbance (R2 = 0.87 and 0.91) and reflectance (R2 = 0.80 and 0.78) for chlorophyll and carotenoids, respectively. Carotenoids showed particularly high and significant correlation coefficients using the partial least squares regression (PLSR) method (R2C = 0.91, R2cv = 0.85, and R2P = 0.90) when associated with hyperspectral absorbance data. Our hypothesis was supported, and these results demonstrate the effectiveness of using two hyperspectral sensors for optical leaf profile analysis and predicting the concentration of photosynthetic pigments using multivariate statistical methods. This method for two sensors is more efficient and shows better results compared to traditional single sensor techniques for measuring chloroplast changes and pigment phenotyping in plants.

Fruit quality and volatile compounds of greenhouse sweet peppers as affected by the LED spectrum of supplementary interlighting

BACKGROUND

Seasonal low light intensity and short photoperiods lead to decreased yield, size, and quality of fruits in the Northern Hemisphere. Recently, supplemental lighting using light-emitting diodes (LEDs) has been introduced to overcome such problems. However, most studies have focused on plant growth or fruit yield but not on taste. This study aimed to evaluate the quality and volatile compounds of greenhouse sweet pepper fruits under three different lighting conditions: natural light only (NL), NL with red/blue interlighting (RB), and NL with red/blue/far-red interlighting (RBFR).

RESULTS

The size, color, firmness, and soluble sugar concentration of the sweet pepper fruit were investigated, and sensory evaluation was conducted by nine trained panelists. Individual fruit fresh weights were higher in the order of RBFR, NL, and RB, with mean values of 219.1, 201.7, and 197.4 g, respectively. Additionally, the composition of volatile compounds demonstrated a distinct clustering pattern by light treatment, implying that the LED interlighting spectra affected the overall taste of sweet pepper fruits. Sensory evaluation indicated that sweetness was higher in the order of RBFR, RB, and NL, with values of 5.28, 4.36, and 3.72, respectively. The soluble sugar results showed the same order as that for the sensory evaluation of sweetness, i.e., RBFR, RB, and NL, with values of 5071, 4647, and 3978 μg ^-1 fresh weight, respectively.

CONCLUSION

Adding far-red to RB interlighting could improve the fruit quality attributes, fruit taste perception, and soluble sugars of sweet peppers compared to those under RB or solely NL. © 2023 Society of Chemical Industry.

Far-Red-Light-Induced Morphology Changes, Phytohormone, and Transcriptome Reprogramming of Chinese Kale (Brassica alboglabra Bailey)

With far-red-light supplementation (3 W·m−2, and 6 W·m−2), the flower budding rate, plant height, internode length, plant display, and stem diameter of Chinese kale were largely elevated, as well as the leaf morphology such as leaf length, leaf width, petiole length, and leaf area. Consequently, the fresh weight and dry weight of the edible parts of Chinese kale were markedly increased. The photosynthetic traits were enhanced, and the mineral elements were accumulated. To further explore the mechanism that far-red light simultaneously promoted the vegetative growth and reproductive growth of Chinese kale, this study used RNA sequencing to gain a global perspective on the transcriptional regulation, combining it with an analysis of composition and content of phytohormones. A total of 1409 differentially expressed genes were identified, involved mainly in pathways related to photosynthesis, plant circadian rhythm, plant hormone biosynthesis, and signal transduction. The gibberellins GA9, GA19, and GA20 and the auxin ME-IAA were strongly accumulated under far-red light. However, the contents of the gibberellins GA4 and GA24, the cytokinins IP and cZ, and the jasmonate JA were significantly reduced by far-red light. The results indicated that the supplementary far-red light can be a useful tool to regulate the vegetative architecture, elevate the density of cultivation, enhance the photosynthesis, increase the mineral accumulation, accelerate the growth, and obtain a significantly higher yield of Chinese kale.

Blue Photons from Broad-Spectrum LEDs Control Growth, Morphology, and Coloration of Indoor Hydroponic Red-Leaf Lettuce

For indoor crop production, blue + red light-emitting diodes (LEDs) have high photosynthetic efficacy but create pink or purple hues unsuitable for workers to inspect crops. Adding green light to blue + red light forms a broad spectrum (white light), which is created by: phosphor-converted blue LEDs that cast photons with longer wavelengths, or a combination of blue, green, and red LEDs. A broad spectrum typically has a lower energy efficiency than dichromatic blue + red light but increases color rendering and creates a visually pleasing work environment. Lettuce growth depends on the interactions of blue and green light, but it is not clear how phosphor-converted broad spectra, with or without supplemental blue and red light, influence crop growth and quality. We grew red-leaf lettuce 'Rouxai' in an indoor deep-flow hydroponic system at 22 °C air temperature and ambient CO₂. Upon germination, plants received six LED treatments delivering different blue fractions (from 7% to 35%) but the same total photon flux density (400 to 799 nm) of 180 μmol·m^-2·s^-1 under a 20 h photoperiod. The six LED treatments were: (1) warm white (WW₁₈₀); (2) mint white (MW₁₈₀); (3) MW₁₀₀ + blue₁₀ + red₇₀; (4) blue₂₀ + green₆₀ + red₁₀₀; (5) MW₁₀₀ + blue₅₀ + red₃₀; and (6) blue₆₀ + green₆₀ + red₆₀. Subscripts denote photon flux densities in μmol·m^-2·s^-1. Treatments 3 and 4 had similar blue, green, and red photon flux densities, as did treatments 5 and 6. At the harvest of mature plants, lettuce biomass, morphology, and color were similar under WW₁₈₀ and MW₁₈₀, which had different green and red fractions but similar blue fractions. As the blue fraction in broad spectra increased, shoot fresh mass, shoot dry mass, leaf number, leaf size, and plant diameter generally decreased and red leaf coloration intensified. Compared to blue + green + red LEDs, white LEDs supplemented with blue + red LEDs had similar effects on lettuce when they delivered similar blue, green, and red photon flux densities. We conclude that the blue photon flux density in broad spectra predominantly controls lettuce biomass, morphology, and coloration.

Active and passive chlorophyll fluorescence measurements at canopy level on potato crops. Evidence of similitude of diurnal cycles of apparent fluorescence yields

We performed active and passive measurements of diurnal cycles of chlorophyll fluorescence on potato crops at canopy level in outdoors conditions for 26 days. Active measurements of the stationary fluorescence yield (Fs) were performed using Ledflex, a fluorescence micro-LIDAR described in Moya et al. (Photosynth Res 142:1-15, 2019), capable of remote measurements of chlorophyll fluorescence under full sun-light in the wavelength range from 650 to 800 nm. Passive measurements of solar-induced fluorescence (SIF) fluxes were performed with Spectroflex, an instrument based on the method of filling-in in the O₂A and O₂B absorption bands at 760 nm (F760) and 687 nm (F687), respectively.Diurnal cycles of Fs showed significant variations throughout the day, directly attributed to changes in photosystem II yield. Contrasting patterns were observed according to illumination conditions. Under cloudy sky, Fs varied in parallel with photosynthetically active radiation (PAR). By contrast, during clear sky days, the diurnal cycle of Fs showed a "M" shape pattern with a minimum around noon.F687 and F760 showed different patterns, according to illumination conditions. Under low irradiance associated with cloudy conditions, F687 and F760 followed similar diurnal patterns, in parallel with PAR. Under high irradiance associated with clear sky we observed an increase of the F760/F687 ratio, which we attributed to the contributions in the 760 nm emission of photosystem I fluorescence from deeper layers of the leaves, on one end, and by the decrease of 687 nm emission as a result of red fluorescence re-absorption, on the other end.We defined an approach to derive a proxy of fluorescence yield (FYSIF) from SIF measurements as a linear combination of F687 and F760 normalized by vegetation radiance, where the coefficients of the linear combination were derived from the spectral transmittance of Ledflex. We demonstrated a close relationship between diurnal cycles of FYSIF and Fs, which outperformed other approaches based on normalization by incident light.

Spectral-conversion film potential for greenhouses: Utility of green-to-red photons conversion and far-red filtration for plant growth

Although green (G, 500 to 600 nm) and far-red (FR, 700 to 800 nm) light play important roles in regulating plant growth and development, they are often considered less useful at stimulating photosynthesis than red (R, 600 to 700 nm) and blue (B, 400 to 500 nm) light. Based on this perception, approaches to modifying the transmission of greenhouse glazing materials include (1) conversion of G photons from sunlight into R photons and (2) exclusion of the near-infrared (>700 nm) fraction of sunlight. We evaluated these approaches using simulated scenarios with light-emitting diodes to determine how partial and complete substitution of G with R light and exclusion of FR light affected the growth of lettuce and tomato grown indoors. The substitution of G with R light had little or no effect on fresh and dry mass of tomato. However, with the presence of FR light, fresh and dry mass of lettuce increased by 22-26% as G light was increasingly substituted with R light. In tomato, excluding FR inhibited plant height, leaf area, and dry mass by 60-71%, 10-37%, and 20-44%, respectively. Similarly, in lettuce, excluding FR inhibited plant diameter, leaf length, and dry mass by 15-23%, 23-33%, or 28-48%, respectively. We conclude that the spectral conversion of G-to-R photons can promote plant growth in at least some crop species, such as lettuce, while the exclusion of FR decreases crop growth and yield.

A Novel LED Light Radiation Approach Enhances Growth in Green and Albino Tea Varieties

Light, as an energy source, has been proven to strongly affect photosynthesis and, thus, can regulate the yield and quality of tea leaves (Camellia sinensis L.). However, few comprehensive studies have investigated the synergistic effects of light wavelengths on tea growth and development in green and albino varieties. Thus, the objective of this study was to investigate different ratios of red, blue and yellow light and their effects on tea plants' growth and quality. In this study, Zhongcha108 (green variety) and Zhongbai4 (albino variety) were exposed to lights of different wavelengths for a photoperiod of 5 months under the following seven treatments: white light simulated from the solar spectrum, which served as the control, and L1 (red 75%, blue 15% and yellow 10%), L2 (red 60%, blue 30% and yellow 10%), L3 (red 45%, far-red light 15%, blue 30% and yellow 10%), L4 (red 55%, blue 25% and yellow 20%), L5 (red 45%, blue 45% and yellow 10%) and L6 (red 30%, blue 60% and yellow 10%), respectively. We examined how different ratios of red light, blue light and yellow light affected tea growth by investigating the photosynthesis response curve, chlorophyll content, leaf structure, growth parameters and quality. Our results showed that far-red light interacted with red, blue and yellow light (L3 treatments) and significantly promoted leaf photosynthesis by 48.51% in the green variety, Zhongcha108, compared with the control treatments, and the length of the new shoots, number of new leaves, internode length, new leaf area, new shoots biomass and leaf thickness increased by 70.43%, 32.64%, 25.97%, 15.61%, 76.39% and 13.30%, respectively. Additionally, the polyphenol in the green variety, Zhongcha108, was significantly increased by 15.6% compared to that of the plants subjected to the control treatment. In addition, for the albino variety Zhongbai4, the highest ratio of red light (L1 treatment) remarkably enhanced leaf photosynthesis by 50.48% compared with the plants under the control treatment, resulting in the greatest new shoot length, number of new leaves, internode length, new leaf area, new shoot biomass, leaf thickness and polyphenol in the albino variety, Zhongbai4, compared to those of the control treatments, which increased by 50.48%, 26.11%, 69.29%, 31.61%, 42.86% and 10.09%, respectively. Our study provided these new light modes to serve as a new agricultural method for the production of green and albino varieties.

Emergent molecular traits of lettuce and tomato grown under wavelength-selective solar cells

The integration of semi-transparent organic solar cells (ST-OSCs) in greenhouses offers new agrivoltaic opportunities to meet the growing demands for sustainable food production. The tailored absorption/transmission spectra of ST-OSCs impacts the power generated as well as crop growth, development and responses to the biotic and abiotic environments. To characterize crop responses to ST-OSCs, we grew lettuce and tomato, traditional greenhouse crops, under three ST-OSC filters that create different light spectra. Lettuce yield and early tomato development are not negatively affected by the modified light environment. Our genomic analysis reveals that lettuce production exhibits beneficial traits involving nutrient content and nitrogen utilization while select ST-OSCs impact regulation of flowering initiation in tomato. These results suggest that ST-OSCs integrated into greenhouses are not only a promising technology for energy-neutral, sustainable and climate-change protected crop production, but can deliver benefits beyond energy considerations.

Oxygenic photosynthetic responses of cyanobacteria exposed under an M-dwarf starlight simulator: Implications for exoplanet's habitability

INTRODUCTION

The search for life on distant exoplanets is expected to rely on atmospheric biosignatures detection, such as oxygen of biological origin. However, it is not demonstrated how much oxygenic photosynthesis, which on Earth depends on visible light, could work under spectral conditions simulating exoplanets orbiting the Habitable Zone of M-dwarf stars, which have low light emission in the visible and high light emission in the far-red/near-infrared. By utilizing cyanobacteria, the first organisms to evolve oxygenic photosynthesis on our planet, and a starlight simulator capable of accurately reproducing the emission spectrum of an M-dwarf in the range 350-900 nm, we could answer this question.

METHODS

We performed experiments with the cyanobacterium Chlorogloeopsis fritschii PCC6912, capable of Far-Red Light Photoacclimation (FaRLiP), which allows the strain to harvest far-red in addition to visible light for photosynthesis, and Synechocystis sp. PCC6803, a species unable to perform this photoacclimation, comparing their responses when exposed to three simulated light spectra: M-dwarf, solar and far-red. We analysed growth and photosynthetic acclimation features in terms of pigment composition and photosystems organization. Finally, we determined the oxygen production of the strains directly exposed to the different spectra.

RESULTS

Both cyanobacteria were shown to grow and photosynthesize similarly under M-dwarf and solar light conditions: Synechocystis sp. by utilizing the few photons in the visible, C. fritschii by harvesting both visible and far-red light, activating the FaRLiP response.

DISCUSSION

Our results experimentally show that an M-dwarf light spectrum could support a biological oxygen production similar to that in solar light at the tested light intensities, suggesting the possibility to discover such atmospheric biosignatures on those exoplanets if other boundary conditions are met.

Designing plant-transparent agrivoltaics

Covering greenhouses and agricultural fields with photovoltaics has the potential to create multipurpose agricultural systems that generate revenue through conventional crop production as well as sustainable electrical energy. In this work, we evaluate the effects of wavelength-selective cutoffs of visible and near-infrared (biologically active) radiation using transparent photovoltaic (TPV) absorbers on the growth of three diverse, representative, and economically important crops: petunia, basil, and tomato. Despite the differences in TPV harvester absorption spectra, photon transmission of photosynthetically active radiation (PAR; 400-700 nm) is the most dominant predictor of crop yield and quality. This indicates that different wavebands of blue, red, and green are essentially equally important to these plants. When the average photosynthetic daily light integral is > 12 mol m^-2 d^-1, basil and petunia yield and quality is acceptable for commercial production. However, even modest decreases in TPV transmission of PAR reduces tomato growth and fruit yield. These results identify crop-specific design requirements that exist for TPV harvester transmission and the necessity to maximize transmission of PAR to create the most broadly applicable TPV greenhouse harvesters for diverse crops and geographic locations. We determine that the deployment of 10% power conversion efficiency (PCE) plant-optimized TPVs over approximately 10% of total agricultural and pasture land in the U.S. would generate 7 TW, nearly double the entire energy demand of the U.S.

Growth, Biomass Partitioning, and Photosynthetic Performance of Chrysanthemum Cuttings in Response to Different Light Spectra

Chrysanthemum (Chrysanthemum morifolium) is among the most popular ornamental plants, propagated mainly through stem cuttings. There is a lack of information regarding the impact of the lighting environment on the successful production of cuttings and underlying mechanisms. The light spectrum affects plant morphology, growth, and photosynthesis. In the present study, chrysanthemum, cv. 'Katinka' cuttings, were exposed to five lighting spectra, including monochromatic red (R), blue (B) lights, and multichromatic lights, including a combination of R and B (R:B), a combination of R, B, and far red (R:B:FR) and white (W), for 30 days. B light enhanced areal growth, as indicated by a higher shoot mass ratio, while R light directed the biomass towards the underground parts of the cuttings. Monochromatic R and B lights promoted the emergence of new leaves. In contrast, individual leaf area was largest under multichromatic lights. Exposing the cuttings to R light led to the accumulation of carbohydrates in the leaves. Cuttings exposed to multichromatic lights showed higher chlorophyll content than monochromatic R- and B-exposed cuttings. Conversely, carotenoid and anthocyanin contents were the highest in monochromatic R- and B-exposed plants. B-exposed cuttings showed higher photosynthetic performance, exhibited by the highest performance index on the basis of light absorption, and maximal quantum yield of PSII efficiency. Although R light increased biomass toward roots, B light improved above-ground growth, photosynthetic functionality, and the visual performance of Chrysanthemum cuttings.

Rajput V, Kumar Singh R, Guo Y, Kosolapov A, Usova E, Varduny T, Chalenko E, Yadronova O, Dmitriev P, Zaruba T. Chlorophyll fluorometry in evaluating photosynthetic performance: key limitations, possibilities, perspectives and alternatives

Non-destructive methods for the assessment of photosynthetic parameters of plants are widely applied to evaluate rapidly the photosynthetic performance, plant health, and shifts in plant productivity induced by environmental and cultivation conditions. Most of these methods are based on measurements of chlorophyll fluorescence kinetics, particularly on pulse modulation (PAM) fluorometry. In this paper, fluorescence methods are critically discussed in regard to some their possibilities and limitations inherent to vascular plants and microalgae. Attention is paid to the potential errors related to the underestimation of thylakoidal cyclic electron transport and anoxygenic photosynthesis. PAM-methods are also observed considering the color-addressed measurements. Photoacoustic methods are discussed as an alternative and supplement to fluorometry. Novel Fourier modifications of PAM-fluorometry and photoacoustics are noted as tools allowing simultaneous application of a dual or multi frequency measuring light for one sample.

Facing energy limitations - approaches to increase basil (Ocimum basilicum L.) growth and quality by different increasing light intensities emitted by a broadband LED light spectrum (400-780 nm)

Based on the current trend towards broad-bandwidth LED light spectra for basil productions in multi-tiered controlled-environment horticulture, a recently developed white broad-bandwidth LED light spectrum (400-780 nm) including far-red wavelengths with elevated red and blue light fractions was employed to cultivate basil. Four Ocimum basilicum L. cultivars (cv. Anise, cv. Cinnamon, cv. Dark Opal and cv. Thai Magic) were exposed to two different rising light intensity conditions (I_Low and I_High). In dependence of the individual cultivar-specific plant height increase over time, basil cultivars were exposed to light intensities increasing from ~ 100 to ~ 200 µmol m^-2 s^-1 under I_Low, and from 200 to 400 µmol m^-2 s^-1 under I_High (due to the exponential light intensity increases with decreasing proximity to the LED light fixtures). Within the first experiment, basils' morphological developments, biomass yields and time to marketability under both light conditions were investigated and the energy consumptions were determined to calculate the basils' light use efficiencies. In detail, cultivar-dependent differences in plant height, leaf and branch pair developments over time are described. In comparison to the I_Low light conditions, I_High resulted in accelerated developments and greater yields of all basil cultivars and expedited their marketability by 3-5 days. However, exposure to light intensities above ~ 300 µmol m^-2 s^-1 induced light avoidance responses in the green-leafed basil cultivars cv. Anise, cv. Cinnamon and cv. Thai Magic. In contrast, I_Low resulted in consumer-preferred visual qualities and greater biomass efficiencies of the green-leafed basil cultivars and are discussed as a result of their ability to adapt well to low light conditions. Contrarily to the green-leafed cultivars, purple-leafed cv. Dark Opal developed insufficiently under I_Low, but remained light-tolerant under I_High, which is related to its high anthocyanin contents. In a second experiment, cultivars' volatile organic compound (VOC) contents and compositions over time were investigated. While VOC contents per gram of leaf dry matter gradually decreased in purple-leafed cv. Dark Opal between seedling stage to marketability, their contents gradually increased in the green cultivars. Regardless of the light treatment applied, cultivar-specific VOC compositions changed tremendously in a developmental stage-dependent manner.

Far-Red Light Effects on Lettuce Growth and Morphology in Indoor Production Are Cultivar Specific

Understanding crop responses to the light spectrum is critical for optimal indoor production. Far-red light is of particular interest, because it can accelerate growth through both physiological and morphological mechanisms. However, the optimal amount of supplemental far-red light for indoor lettuce production is yet to be quantified. Lettuce 'Cherokee', 'Green SaladBowl', and 'Little Gem' were grown under 204 µmol·m-2·s-1 warm-white light-emitting diodes (LEDs) with supplemental far-red ranging from 5.3 to 75.9 µmol·m-2·s-1. Supplemental far-red light increased canopy light interception 5 days after the start of far-red light treatment (DAT) for 'Green SaladBowl' and 'Little Gem' and 7 DAT for 'Cherokee'. The increase in light interception was no longer evident after 12 and 16 DAT for 'Green SaladBowl' and 'Little Gem', respectively. We did not find evidence that supplemental far-red light increased leaf-level photosynthesis. At the final harvest, shoot dry weights of 'Cherokee' and 'Little Gem' increased by 39.4% and 19.0%, respectively, while 'Green SaladBowl' was not affected. In conclusion, adding far-red light in indoor production increased light interception during early growth and likely increased whole plant photosynthesis thus growth, but those effects were cultivar-specific; the increase in dry weight was linear up to 75.9 µmol·m-2·s-1 far-red light.

Photosynthesis in sun and shade: the surprising importance of far-red photons

The current definition of photosynthetically active radiation includes only photons from 400 up to 700 nm, despite evidence of the synergistic interaction between far-red photons and shorter-wavelength photons. The synergy between far-red and shorter-wavelength photons has not been studied in sunlight under natural conditions. We used a filter to remove photons above 700 nm to quantify the effects on photosynthesis in diverse species under full sun, medium light intensity and vegetation shade. Far-red photons (701 to 750 nm) in sunlight are used efficiently for photosynthesis. This is especially important for leaves in vegetation shade, where far-red photons can be > 50% of the total incident photons between 400 and 750 nm. Far-red photons accounted for 24-25% of leaf gross photosynthesis (P_gross ) in a C₃ and a C₄ species when sunlight was filtered through a leaf, and 10-14% of leaf P_gross in a tree and an understory species in deep shade. Accounting for the photosynthetic activity of far-red photons is critical for accurate measurement and modeling of photosynthesis at single leaf, canopy and ecosystem scales. This, in turn, is crucial in understanding crop productivity, the global carbon cycle and climate change impacts on agriculture and ecosystems.

High levels of anoxygenic photosynthesis revealed by dual-frequency Fourier photoacoustics in Ailanthus altissima leaves

In contrast to oxygenic photosynthesis, true anoxygenic photosynthesis is not associated with O2 evolution originated from water photolysis but still converts light energy to that of the phosphoanhydride bonds of ATP. In a narrow sense, anoxygenic photosynthesis is mainly known as to be related to the purple and green sulfur bacteria, but in a broad sense, it also occurs in the vascular plants. The portion of photosynthetic water photolysis that is compensated by the processes of O2 uptake (respiration, photorespiration, Mehler cycle, etc.) may be referred to as 'quasi' anoxygenic photosynthesis. Photoacoustic method allows for the separate detection of photolytic O2 at frequencies of measuring light about 20-40Hz, whereas at 250-400Hz, it detects the photochemical energy storage. We have developed a fast-Fourier transform photoacoustic method enabling measurements of both these signals simultaneously in one sample. This method allows to calculate oxygenic coefficients, which reflect the part of photochemically stored light energy that is used for the water photolysis. We show that the true anoxygenic photosynthesis in Ailanthus altissima Mill. leaves reached very high levels under low light, under moderate light at the beginning of the 1-h period, and at the end of the 40-min period under saturating light.

Using hyperspectral leaf reflectance to estimate photosynthetic capacity and nitrogen content across eastern cottonwood and hybrid poplar taxa

Eastern cottonwood (Populus deltoides W. Bartram ex Marshall) and hybrid poplars are well-known bioenergy crops. With advances in tree breeding, it is increasingly necessary to find economical ways to identify high-performing Populus genotypes that can be planted under different environmental conditions. Photosynthesis and leaf nitrogen content are critical parameters for plant growth, however, measuring them is an expensive and time-consuming process. Instead, these parameters can be quickly estimated from hyperspectral leaf reflectance if robust statistical models can be developed. To this end, we measured photosynthetic capacity parameters (Rubisco-limited carboxylation rate (Vcmax), electron transport-limited carboxylation rate (Jmax), and triose phosphate utilization-limited carboxylation rate (TPU)), nitrogen per unit leaf area (Narea), and leaf reflectance of seven taxa and 62 genotypes of Populus from two study plantations in Mississippi. For statistical modeling, we used least absolute shrinkage and selection operator (LASSO) and principal component analysis (PCA). Our results showed that the predictive ability of LASSO and PCA models was comparable, except for Narea in which LASSO was superior. In terms of model interpretability, LASSO outperformed PCA because the LASSO models needed 2 to 4 spectral reflectance wavelengths to estimate parameters. The LASSO models used reflectance values at 758 and 935 nm for estimating Vcmax (R2 = 0.51 and RMSPE = 31%) and Jmax (R2 = 0.54 and RMSPE = 32%); 687, 746, and 757 nm for estimating TPU (R2 = 0.56 and RMSPE = 31%); and 304, 712, 921, and 1021 nm for estimating Narea (R2 = 0.29 and RMSPE = 21%). The PCA model also identified 935 nm as a significant wavelength for estimating Vcmax and Jmax. Therefore, our results suggest that hyperspectral leaf reflectance modeling can be used as a cost-effective means for field phenotyping and rapid screening of Populus genotypes because of its capacity to estimate these physicochemical parameters.

The Electronic Origin of Far-Red-Light-Driven Oxygenic Photosynthesis

Photosystem‐II uses sunlight to trigger charge separation and catalyze water oxidation. Intrinsic properties of chlorophyll a pigments define a natural “red limit” of photosynthesis at ≈680 nm. Nevertheless, charge separation can be triggered with far‐red photons up to 800 nm, without altering the nature of light‐harvesting pigments. Here we identify the electronic origin of this remarkable phenomenon using quantum chemical and multiscale simulations on a native Photosystem‐II model. We find that the reaction center is preorganized for charge separation in the far‐red region by specific chlorophyll–pheophytin pairs, potentially bypassing the light‐harvesting apparatus. Charge transfer can occur along two distinct pathways with one and the same pheophytin acceptor (Pheo_D1). The identity of the donor chlorophyll (Chl_D1 or P_D1) is wavelength‐dependent and conformational dynamics broaden the sampling of the far‐red region by the two charge‐transfer states. The two pathways rationalize spectroscopic observations and underpin designed extensions of the photosynthetically active radiation limit.

Leaf microscopy applications in photosynthesis research: identifying the gaps

Leaf imaging via microscopy has provided critical insights into research on photosynthesis at multiple junctures, from the early understanding of the role of stomata, through elucidating C4 photosynthesis via Kranz anatomy and chloroplast arrangement in single cells, to detailed explorations of diffusion pathways and light utilization gradients within leaves. In recent decades, the original two-dimensional (2D) explorations have begun to be visualized in three-dimensional (3D) space, revising our understanding of structure-function relationships between internal leaf anatomy and photosynthesis. In particular, advancing new technologies and analyses are providing fresh insight into the relationship between leaf cellular components and improving the ability to model net carbon fixation, water use efficiency, and metabolite turnover rate in leaves. While ground-breaking developments in imaging tools and techniques have expanded our knowledge of leaf 3D structure via high-resolution 3D and time-series images, there is a growing need for more in vivo imaging as well as metabolite imaging. However, these advances necessitate further improvement in microscopy sciences to overcome the unique challenges a green leaf poses. In this review, we discuss the available tools, techniques, challenges, and gaps for efficient in vivo leaf 3D imaging, as well as innovations to overcome these difficulties.