Application timing and duration of LED and HPS supplements differentially influence yield, nutrient bioaccumulation, and light use efficiency of greenhouse basil across seasons

Three primary factors that impact plant growth and development are light quantity, quality, and duration. Commercial growers can manipulate these parameters using light-emitting diodes (LEDs) to optimize biomass yield and plant quality. There is significant potential to synergize supplemental lighting (SL) parameters with seasonal variation of ambient sunlight to optimize crop light use efficiency (LUE), which could increase biomass while reducing SL electricity costs. To determine the best lighting characteristics and durations for different crops, particularly for enhancing the yield and nutritional quality of high-value specialty crops produced in greenhouses during the winter, a thorough efficacy comparison of progressive incremental daily light integrals (DLIs) using LED and high-pressure sodium (HPS) sources is required. The purpose of this study was to compare the effects of differential application timing and DLIs of supplemental blue (B)/red (R) narrowband wavelengths from LED lighting systems and HPS lamps on greenhouse hydroponic basil (Ocimum basilicum var. 'Genovese') production. We assessed edible biomass, nutrient bioaccumulation, and LUE. Nine light treatments included: one non-supplemented natural light (NL) control, two end-of-day (EOD) HPS treatments applied for 6 h and 12 h, five EOD 20B/80R LED treatments applied for 3 h, 6 h, 9 h, 12 h, 18 h, and one continuous LED treatment (24 h). Each SL treatment provided 100 µmol·m-2·s-1. The DLI of the NL control averaged 9.9 mol·m-2·d-1 during the growth period (ranging from 4 to 20 mol·m-2·d-1). SL treatments and growing seasons significantly impacted biomass and nutrient bioaccumulation; some SL treatments had lower yields than the non-supplemented NL control. January growing season produced the lowest fresh mass (FM) and dry mass (DM) values compared to November, which had the highest. Mineral analyses revealed that both growing seasons and lighting types impacted macro and micronutrient accumulation. Additionally, the efficiency of each treatment in converting electrical energy into biomass varied greatly. EOD supplements using LED and HPS lighting systems both have merits for efficiently optimizing yield and nutrient accumulation in basil; however, biomass and nutrient tissue concentrations highly depend on seasonal variation in ambient sunlight in conjunction with a supplement's spectral quality, DLI, and application schedule.

Photosynthetic Photon Flux Density Effects on Portulaca olearacea in Controlled-Environment Agriculture

This study aims to evaluate the impacts of the lighting photosynthetic photon flux density (PPFD) on the growth, photosynthesis, and antioxidant response of common purslane (Portulaca oleracea) cultivars to determine energy-efficient lighting strategies for CEA. Green and golden purslane cultivars were cultivated in CEA chambers and four experimental treatments consisting of PPFDs of 150, 200, 250, and 300 ± 10 µmol m-2s-1 were performed, representing daily light integrals (DLIs) of 8.64-17.28 mol m-2d-1 throughout a 16 h photoperiod. The results show that photoresponses to light PPFDs are cultivar-specific. The green cultivar accumulates 174% more dry weight at 300 PPFD compared to the golden cultivar, and also has a higher LUE, but a lower ETR. Dry weight accumulation, plant height, and leaf area dependence on light intensity do not highlight the economic significance of light PPFD/DLI. The derivative parameter (Δ fresh weight (%)/ΔDLI %) more efficiently explains how the percentage increase in DLI due to an increased PPFD affects the percentage of biomass gain between these PPFD treatments. For both cultivars, the relative fresh weight gain is maximal when the lighting PPFD increases from 200 to 250 µmol m-2s-1 and declines with PPFD increases from 250 to 300.

Quantifying the effect of shade on cuticle morphology and carbon isotopes of sycamores: present and past

PREMISE

Reconstructing the light environment and architecture of the plant canopy from the fossil record requires the use of proxies, such as those derived from cell wall undulation, cell size, and carbon isotopes. All approaches assume that plant taxa will respond predictably to changes in light environments. However, most species-level studies looking at cell wall undulation only consider "sun" or "shade" leaves; therefore, we need a fully quantitative taxon-specific method.

METHODS

We quantified the response of cell wall undulation, cell size, and carbon isotopes of Platanus occidentalis using two experimental setups: (1) two growth chambers at low and high light and (2) a series of outdoor growth experiments using green and black shade cloth at different densities. We then developed and applied a proxy for daily light integral (DLI) to fossil Platanites leaves from two early Paleocene floras from the San Juan Basin in New Mexico.

RESULTS

All traits responded to light environment. Cell wall undulation was the most useful trait for reconstructing DLI in the geological record. Median reconstructed DLI from early Paleocene leaves was ~44 mol m^-2  d^-1 , with values from 28 to 54 mol m^-2  d^-1 .

CONCLUSIONS

Cell wall undulation of P. occidentalis is a robust, quantifiable measurement of light environment that can be used to reconstruct the paleo-light environment from fossil leaves. The distribution of high DLI values from fossil leaves may provide information on canopy architecture; indicating that either (1) most of the canopy mass is within the upper portion of the crown or (2) leaves exposed to more sunlight are preferentially preserved.

Increased Plant Quality, Greenhouse Productivity and Energy Efficiency with Broad-Spectrum LED Systems: A Case Study for Thyme (Thymus vulgaris L.)

A light-emitting diode (LED) system covering plant-receptive wavebands from ultraviolet to far-red radiation (360 to 760 nm, “white” light spectrum) was investigated for greenhouse productions of Thymus vulgaris L. Biomass yields and amounts of terpenoids were examined, and the lights’ productivity and electrical efficiency were determined. All results were compared to two conventionally used light fixture types (high-pressure sodium lamps (HPS) and fluorescent lights (FL)) under naturally low irradiation conditions during fall and winter in Berlin, Germany. Under LED, development of Thymus vulgaris L. was highly accelerated resulting in distinct fresh yield increases per square meter by 43% and 82.4% compared to HPS and FL, respectively. Dry yields per square meter also increased by 43.1% and 88.6% under LED compared to the HPS and FL lighting systems. While composition of terpenoids remained unaffected, their quantity per gram of leaf dry matter significantly increased under LED and HPS as compared to FL. Further, the power consumption calculations revealed energy savings of 31.3% and 20.1% for LED and FL, respectively, compared to HPS. In conclusion, the implementation of a broad-spectrum LED system has tremendous potential for increasing quantity and quality of Thymus vulgaris L. during naturally insufficient light conditions while significantly reducing energy consumption.

Leveraging Controlled-Environment Agriculture to Increase Key Basil Terpenoid and Phenylpropanoid Concentrations: The Effects of Radiation Intensity and CO2 Concentration on Consumer Preference

Altering the radiation intensity in controlled environments can influence volatile organic compound (VOC) biosynthetic pathways, including those of terpenoids and phenylpropanoids. In turn, the concentrations of these compounds can have a profound effect on flavor and sensory attributes. Because sweet basil (Ocimum basilicum) is a popular culinary herb, our objectives were to (1) determine the extent radiation intensity and carbon dioxide (CO₂) concentration influence seedling terpenoid and phenylpropanoid concentrations; (2) determine if differences in phenylpropanoid and terpenoid concentrations influence consumer preference; and (3) characterize consumer preferences to better inform production and marketing strategies. "Nufar" sweet basil was grown with CO₂ concentrations of 500 or 1,000 μmol ⋅ mol^-1 under sole-source radiation intensities of 100, 200, 400, or 600 μmol ⋅ m^-2 ⋅ s^-1 with a 16 h photoperiod to create daily light integrals of 6, 12, 23, and 35 mol ⋅ m^-2 ⋅ d^-1. After 2 weeks, concentrations of the terpenoids 1,8 cineole and linalool and the phenylpropanoids eugenol and methyl chavicol were quantified, and consumer sensory panel evaluations were conducted to quantify preferences. Overall, increasing radiation intensity from 100 to 600 μmol ⋅ m^-2 ⋅ s^-1 increased 1,8 cineole, linalool, and eugenol concentrations 2. 4-, 8. 8-, and 3.3-fold, respectively, whereas CO₂ concentration did not influence VOCs. Contrary to our hypothesis, increased VOC concentrations were not correlated with consumer preference. However, overall liking was correlated with aftertaste and flavor. The conclusion that consumer preference is dependent on flavor can be drawn. However, increasing VOC concentrations to increase flavor did not improve flavor preference. Many consumer sensory preference characteristics (favorable preference for aftertaste, bitterness/sweetness, color, flavor, overall liking, and texture) were correlated with basil grown under a radiation intensity of 200 μmol ⋅ m^-2 ⋅ s^-1. This led us to determine that consumers prefer to detect the characteristic basil flavor made up of 1,8 cineole, eugenol, and linalool, which was not as prevalent in basil grown under 100 μmol ⋅ m^-2 ⋅ s^-1, but too high in basil grown under 400 and 600 μmol ⋅ m^-2 ⋅ s^-1, which led to lower consumer preference.

Lighting intensity and photoperiod serves tailoring nitrate assimilation indices in red and green baby leaf lettuce

BACKGROUND

Understanding plant responses to light quantity in indoor horticultural systems is important for optimising lettuce growth and metabolism as well as energy utilisation efficiency. Light intensity and photoperiod sufficient for normal plant growth parameters might be not efficient for nitrate assimilation. Therefore, this study explored and compared the effects of different light intensities (100-500 μmol m-2 s-1 ) and photoperiods (12-24 h) on the growth and nitrate assimilation in red and green leaf lettuce (Lactuca sativa L.).

RESULTS

For efficient nitrate assimilation, 300-400 μmol m-2 s-1 photosynthetic photon flux density (PPFD) and 16-18 h photoperiod is necessary for red and green lettuces. The insufficient light quantity resulted in reduced growth and remarkable increase in nitrate and nitrite contents in both cultivars. Short photoperiods, similarly to low PPFD, growth parameters, chlorophyll indices and nitrate assimilation indices showed the shortage of photosynthetic products for normal plant physiological processes. Short photoperiods had the least pronounced effect on nitrate and nitrite contents in lettuce leaves.

CONCLUSION

Light intensity was superior compared to photoperiods for efficient nitrate assimilation in both lettuce cultivars. Under short photoperiods, similarly to low intensity, growth parameters, chlorophyll index and nitrate assimilation indices showed a shortage of photosynthetic products for normal physiological processes. The free amino acid concentration increased, but it was not efficiently incorporated in proteins, as their level in lettuce was lower compared to those for moderate photoperiods. © 2019 Society of Chemical Industry.