Towards a tailored indoor horticulture: a functional genomics guided phenotypic approach

The role of lanthanide luminescence in advancing technology

Our society is indebted to the numerous inventors and scientists who helped bring about the incredible technological advances in modern society that we all take for granted. The importance of knowing the history of these inventions is often underestimated, although our reliance on technology is escalating. Lanthanide luminescence has paved the way for many of these inventions, from lighting and displays to medical advancements and telecommunications. Given the significant role of these materials in our daily lives, knowingly or not, their past and present applications are reviewed. A majority of the discussion is devoted to pointing out the benefits of using lanthanides over other luminescent species. We aimed to give a short outlook outlines promising directions for the development of the considered field. This review aims to provide the reader enough content to further appreciate the benefits that these technologies have brought into our lives, with the perspective of travelling among the past and latest advances in lanthanide research, aiming for an even brighter future.

LED Lighting to Produce High-Quality Ornamental Plants

The flexibility of LED technology, in terms of energy efficiency, robustness, compactness, long lifetime, and low heat emission, as well as its applications as a sole source or supplemental lighting system, offers interesting potential, giving the ornamental industry an edge over traditional production practices. Light is a fundamental environmental factor that provides energy for plants through photosynthesis, but it also acts as a signal and coordinates multifaceted plant-growth and development processes. With manipulations of light quality affecting specific plant traits such as flowering, plant architecture, and pigmentation, the focus has been placed on the ability to precisely manage the light growing environment, proving to be an effective tool to produce tailored plants according to market request. Applying lighting technology grants growers several productive advantages, such as planned production (early flowering, continuous production, and predictable yield), improved plant habitus (rooting and height), regulated leaf and flower color, and overall improved quality attributes of commodities. Potential LED benefits to the floriculture industry are not limited to the aesthetic and economic value of the product obtained; LED technology also represents a solid, sustainable option for reducing agrochemical (plant-growth regulators and pesticides) and energy inputs (power energy).

LED omics in Rocket Salad (Diplotaxis tenuifolia): Comparative Analysis in Different Light-Emitting Diode (LED) Spectrum and Energy Consumption

By applying three different LED light treatments, designated as blue (B), red (R)/blue (B), red (R) and white (W) light, as well as the control, the effect on Diplotaxis tenuifolia phenotype (yield and quality), and physiological, biochemical, and molecular status, as well as growing system resource use efficiency, was examined. We observed that basic leaf characteristics, such as leaf area, leaf number, relative chlorophyll content, as well as root characteristics, such as total root length and root architecture, remained unaffected by different LEDs. Yield expressed in fresh weight was slightly lower in LED lights than in the control (1113 g m^-2), with R light producing the least (679 g m^-2). However, total soluble solids were significantly affected (highest, 5.5° Brix, in R light) and FRAP was improved in all LED lights (highest, 191.8 μg/g FW, in B) in comparison to the control, while the nitrate content was less (lowest, 949.2 μg/g FW, in R). Differential gene expression showed that B LED light affected more genes in comparison to R and R/B lights. Although total phenolic content was improved under all LED lights (highest, 1.05 mg/g FW, in R/B), we did not detect a significant amount of DEGs in the phenylpropanoid pathway. R light positively impacts the expression of the genes encoding for photosynthesis components. On the other hand, the positive impact of R light on SSC was possibly due to the expression of key genes being induced, such as SUS1. In summary, this research is an integrative and innovative study, where the exploration of the effect of different LED lights on rocket growing under protected cultivation, in a closed chamber cultivation system, was performed at multiple levels.

Integration of Light and Auxin Signaling in Shade Plants: From Mechanisms to Opportunities in Urban Agriculture

With intensification of urbanization throughout the world, food security is being threatened by the population surge, frequent occurrence of extreme climate events, limited area of available cultivated land, insufficient utilization of urban space, and other factors. Determining the means by which high-yielding and high-quality crops can be produced in a limited space is an urgent priority for plant scientists. Dense planting, vertical production, and indoor cultivation are effective ways to make full use of space and improve the crop yield. The results of physiological and molecular analyses of the model plant species Arabidopsis thaliana have shown that the plant response to shade is the key to regulating the plant response to changes in light intensity and quality by integrating light and auxin signals. In this study, we have summarized the major molecular mechanisms of shade avoidance and shade tolerance in plants. In addition, the biotechnological strategies of enhancing plant shade tolerance are discussed. More importantly, cultivating crop varieties with strong shade tolerance could provide effective strategies for dense planting, vertical production, and indoor cultivation in urban agriculture in the future.

Phenotypic Plasticity of Cunninghamialanceolata (Lamb.) Hook. Seedlings in Response to Varied Light Quality Treatments

Effects of light quality on phenotypic plasticity in Cunninghamialanceolata (Lamb.) Hook. seedlings during growth and development, and the underlying mechanisms, were investigated. The seedlings showed distinct morphological adjustments when exposed to an equal photosynthetic photon flux density (400 μmol·m−2·s−1) of different light qualities: monochromatic blue (BL), monochromatic red (RL), monochromatic far-red (FrL), mixed RL and FrL at 1:1 (RFr1:1L), mixed RL and FrL at 1:2 (RFr1:2L), and multi-wavelength white (WL, control). Compared with WL, FrL and BL significantly promoted height increment. However, BL was unfavorable for root growth. The seedling biomass was lower and the root-to-shoot ratio was smaller under BL. RL promoted leaf area enlargement, root growth, axillary bud number, and increased the root-to-shoot ratio, but inhibited stem elongation. Low R/Fr ratios or increased FrL proportion increased seedling stem elongation. The seedling growth under RFr1:1L treatment was poorer than that under other treatments; however, the number of axillary buds was the highest. The plasticity of leaf morphology traits was lower in different treatments, and that of axillary bud traits was crucial in the adaptation of C. lanceolata to light quality. Precise management of light quality and wavelength in controlled environments may maximize the economic efficiency of forest production and enhance its quality.

LED color gradient as a new screening tool for rapid phenotyping of plant responses to light quality

BACKGROUND

The increasing demand for local food production is fueling high interest in the development of controlled environment agriculture. In particular, LED technology brings energy-saving advantages together with the possibility of manipulating plant phenotypes through light quality control. However, optimizing light quality is required for each cultivated plant and specific purpose.

FINDINGS

This article shows that the combination of LED gradient set-ups with imaging-based non-destructive plant phenotyping constitutes an interesting new screening tool with the potential to improve speed, logistics, and information output. To validate this concept, an experiment was performed to evaluate the effects of a complete range of red:blue ratios on 7 plant species: Arabidopsis thaliana, Brachypodium distachyon, Euphorbia peplus, Ocimum basilicum, Oryza sativa, Solanum lycopersicum, and Setaria viridis. Plants were exposed during 30 days to the light gradient and showed significant, but species-dependent, responses in terms of dimension, shape, and color. A time-series analysis of phenotypic descriptors highlighted growth changes but also transient responses of plant shapes to the red:blue ratio.

CONCLUSION

This approach, which generated a large reusable dataset, can be adapted for addressing specific needs in crop production or fundamental questions in photobiology.

Time-Series Growth Prediction Model Based on U-Net and Machine Learning in Arabidopsis

Yield prediction for crops is essential information for food security. A high-throughput phenotyping platform (HTPP) generates the data of the complete life cycle of a plant. However, the data are rarely used for yield prediction because of the lack of quality image analysis methods, yield data associated with HTPP, and the time-series analysis method for yield prediction. To overcome limitations, this study employed multiple deep learning (DL) networks to extract high-quality HTTP data, establish an association between HTTP data and the yield performance of crops, and select essential time intervals using machine learning (ML). The images of Arabidopsis were taken 12 times under environmentally controlled HTPP over 23 days after sowing (DAS). First, the features from images were extracted using DL network U-Net with SE-ResXt101 encoder and divided into early (15-21 DAS) and late (∼21-23 DAS) pre-flowering developmental stages using the physiological characteristics of the Arabidopsis plant. Second, the late pre-flowering stage at 23 DAS can be predicted using the ML algorithm XGBoost, based only on a portion of the early pre-flowering stage (17-21 DAS). This was confirmed using an additional biological experiment (P < 0.01). Finally, the projected area (PA) was estimated into fresh weight (FW), and the correlation coefficient between FW and predicted FW was calculated as 0.85. This was the first study that analyzed time-series data to predict the FW of related but different developmental stages and predict the PA. The results of this study were informative and enabled the understanding of the FW of Arabidopsis or yield of leafy plants and total biomass consumed in vertical farming. Moreover, this study highlighted the reduction of time-series data for examining interesting traits and future application of time-series analysis in various HTPPs.

Testing the hydroponic performance of the edible halophyte Halimione portulacoides, a potential extractive species for coastal Integrated Multi-Trophic Aquaculture

Sea purslane Halimione portulacoides (L.) Aellen is a candidate extractive species for coastal Integrated Multi-Trophic Aquaculture (IMTA) to recycle the dissolved inorganic nitrogen (DIN) and phosphorus (DIP) wasted by excretive species. To test its suitability, saline aquaculture effluents were simulated in the laboratory using a hydroponics approach to cultivate the plants. Nutrient extraction efficiency, growth performance and nutritional profile were assessed under a range of DIN and DIP concentrations representing three different aquaculture intensification regimes and using Hoagland's solution as a control. Over a 10-week period, hydroponic units under non-limited N and P conditions displayed daily extraction rates between 1.5 and 2.8 mg DIN-N L^-1 day^-1 and 0.1-0.2 mg DIP-P L^-1 day^-1 and yielded between 63.0 and 73.0 g m^-2 day^-1 of H. portulacoides biomass. Relatively to biomass produced, H. portulacoides extracted between 2.6 and 4.2 mg DIN-N g^-1 and 0.1-0.4 mg DIP-P g^-1. The treatment with low-input of DIN and DIP (6.4 mg N L^-1 and 0.7 mg P L^-1) induced some degree of nutrient limitation, as suggested by the extremely high extraction efficiencies of DIN extraction (99%) in parallel with lower productivity. The nutritional profile of H. portulacoides leaves is comparable to that of other edible halophytes and leafy greens and could be a low-sodium alternative to salt in its lyophilized form. From the present study, we conclude that the edible halophyte H. portulacoides can be highly productive in hydroponics using saline water irrigation with non-limiting concentrations of DIN and DIP and is, therefore, a suitable extractive species for coastal IMTA in brackish waters.

Monochromatic red light during plant growth decreases the size and improves the functionality of stomata in chrysanthemum

Light emitting diodes (LEDs) now enable precise light quality control. Prior to commercialisation however, the plant response to the resultant light quality regime ought to be addressed. The response was examined here in chrysanthemum by evaluating growth, chlorophyll fluorescence (before and following water deficit), as well as stomatal anatomy (density, size, pore dimensions and aperture heterogeneity) and closing ability. Plants were grown under blue (B), red (R), a mixture of R (70%) and B (RB), or white (W; 41% B, 39% intermediate spectrum, 20% R) light LEDs. Although R light promoted growth, it also caused leaf deformation (epinasty) and disturbed the photosynthetic electron transport system. The largest stomatal size was noted following growth under B light, whereas the smallest under R light. The largest stomatal density was observed under W light. Monochromatic R light stimulated both the rate and the degree of stomatal closure in response to desiccation compared with the other light regimes. We conclude that stomatal size is mainly controlled by the B spectrum, whereas a broader spectral range is important for determining stomatal density. Monochromatic R light enhanced stomatal ability to regulate water loss upon desiccation.

LED Lighting Systems for Horticulture: Business Growth and Global Distribution

In recent years, research on light emitting diodes (LEDs) has highlighted their great potential as a lighting system for plant growth, development and metabolism control. The suitability of LED devices for plant cultivation has turned the technology into a main component in controlled or closed plant-growing environments, experiencing an extremely fast development of horticulture LED metrics. In this context, the present study aims to provide an insight into the current global horticulture LED industry and the present features and potentialities for LEDs’ applications. An updated review of this industry has been integrated through a database compilation of 301 manufacturers and 1473 LED lighting systems for plant growth. The research identifies Europe (40%) and North America (29%) as the main regions for production. Additionally, the current LED luminaires’ lifespans show 10 and 30% losses of light output after 45,000 and 60,000 working hours on average, respectively, while the vast majority of worldwide LED lighting systems present efficacy values ranging from 2 to 3 μmol J−1 (70%). Thus, an update on the status of the horticultural LED sector, LEDs’ applications and metrics, and the intense innovation are described and discussed.

Increasing the Yield of Lactuca sativa, L. in Glass Greenhouses through Illumination Spectral Filtering and Development of an Optical Thin Film Filter

With the increase in world population, the continued advances in modern greenhouse agriculture and plant growth practices are expected to help overcome the global problem of future food shortages. The next generation greenhouse design practices will need to address a range of issues, ranging from energy and land use efficiency to providing plant-optimized growth techniques. In this paper, we focus on investigating the optimum irradiation spectra matched to the lettuce species (Lactuca sativa, L.), commonly grown in greenhouse environments, in order to develop low-emissivity glass panes that maximize the biomass productivity of glass greenhouses. This low-emissivity glass passes the solar spectral components needed for crop growth, while rejecting other unwanted radiations. This could potentially lead to significant energy savings and other beneficial effects related to greenhouse climate control, in a range of climates. The experimental results show that substantial biomass productivity improvements in lettuce (up to approximately 14.7%) can be attained by using spectrally optimized illumination, instead of white light illumination. This optimized wavelength is then demonstrated as being used to develop an advanced metal-dielectric thin-film filter that produces the optimized illumination spectrum when exposed to sunlight.

Design of highly efficient phosphor-converted white light-emitting diodes with color rendering indices (R1 - R15) ≥ 95 for artificial lighting

Phosphor-converted white light-emitting diodes (pc-WLEDs) are excellent energy-efficient light sources for artificial lighting applications. One goal of artificial lighting is to make objects/images look natural - as they look under the sunlight. The ability of a light source to accurately render the natural color of an object is gauged by the parameter - color rendering index (CRI). A conventional pc-WLED has an average CRI ~ 80, which is very low for accurate color reproduction. To utilize the pc-WLEDs for artificial lighting applications, all the CRI points (R₁ - R₁₅) should be above 95. However, there is a trade-off between CRI and luminous efficacy (LER), and it is challenging to increase both CRI and LER. Herein we propose a novel LED package (PKG) design to achieve CRI points ≥95 and efficiency ~100 lm/W by introducing two blue LEDs and a UV LED in combination with green and red phosphors. The silicone encapsulant, the current through the LEDs, and the green/red phosphor ratio were optimized for achieving high CRI and LER. Our re-designed LED PKG will find applications in stadium lighting as well as for ultra-high-definition television production where high CRI points are required for the artificial light source.

Adding Blue to Red Supplemental Light Increases Biomass and Yield of Greenhouse-Grown Tomatoes, but Only to an Optimum

Greenhouse crop production in northern countries often relies heavily on supplemental lighting for year-round yield and product quality. Among the different spectra used in supplemental lighting, red is often considered the most efficient, but plants do not develop normally when grown solely under monochromatic red light ("red light syndrome"). Addition of blue light has been shown to aid normal development, and typical lighting spectra in greenhouse production include a mixture of red and blue light. However, it is unclear whether sunlight, as part of the light available to plants in the greenhouse, may be sufficient as a source of blue light. In a greenhouse high-wire tomato (Solanum lycopersicum), we varied the percentage of blue supplemental light (in a red background) as 0, 6, 12, and 24%, while keeping total photosynthetically active radiation constant. Light was supplied as a mixture of overhead (99 μmol m-2 s-1) and intracanopy (48 μmol m-2 s-1) LEDs, together with sunlight. Averaged over the whole experiment (111 days), sunlight comprised 58% of total light incident onto the crop. Total biomass, yield and number of fruits increased with the addition of blue light to an optimum, suggesting that both low (0%) and high (24%) blue light intensities were suboptimal for growth. Stem and internode lengths, as well as leaf area, decreased with increases in blue light percentage. While photosynthetic capacity increased linearly with increases in blue light percentage, photosynthesis in the low blue light treatment (0%) was not low enough to suggest the occurrence of the red light syndrome. Decreased biomass at low (0%) blue light was likely caused by decreased photosynthetic light use efficiency. Conversely, decreased biomass at high (24%) blue light was likely caused by reductions in canopy light interception. We conclude that while it is not strictly necessary to add blue light to greenhouse supplemental red light to obtain a functional crop, adding some (6-12%) blue light is advantageous for growth and yield while adding 24% blue light is suboptimal for growth.