Near-infrared Reflective Diffusion Coating Is Beneficial for Asparagus Summer Production in a Simple Plastic Greenhouse

Asparagus is a potential greenhouse crop, and its production is considerably affected by temperature and light, especially in the summer season. This study investigated the effects of the application of near-infrared (NIR)-reflective diffusion coating on a simple plastic greenhouse on microclimatic conditions, plant response, spear yield, and quality of the asparagus plant in central Taiwan. The results showed that NIR-reflective diffusion coating reduced the mean air temperature inside the greenhouse by 0.3 to 0.9 °C and leaf temperature by 2.3, 2.4, and 2.4 °C at a canopy height of 50, 100, and 50 cm, respectively. Although the accumulated daily light integral (DLI) transmitted in the coated greenhouse exhibited an 18.9% reduction compared with a 16.8% reduction in the noncoated greenhouse, a more uniform spatial light distribution was noted. Therefore, photosynthesis improved in the middle and bottom canopy, and plants could maintain a higher transpiration rate, thus resulting in atmospheric cooling. The average spear yield increased by 31.4% in summer and by 10.1% during the following harvest with a lower crude fiber (CF) content and higher Ca as well as Mg contents. In addition, the number of newly emerged shoots increased by 48.8% after the removal of the mother stalk under coating. NIR-reflective diffusion coating can be used as an energy-saving method for enhancing cooling and improving light use efficiency, thus increasing asparagus production in a greenhouse in summer.

Enabling Year-round Cultivation in the Nordics-Agrivoltaics and Adaptive LED Lighting Control of Daily Light Integral

High efficacy LED lamps combined with adaptive lighting control and greenhouse integrated photovoltaics (PV) could enable the concept of year-round cultivation. This concept can be especially useful for increasing the production in the Nordic countries of crops like herbaceous perennials, forest seedlings, and other potted plants not native of the region, which are grown more than one season in this harsh climate. Meteorological satellite data of this region was analyzed in a parametric study to evaluate the potential of these technologies. The generated maps showed monthly average temperatures fluctuating from −20 °C to 20 °C throughout the year. The natural photoperiod and light intensity also changed drastically, resulting in monthly average daily light integral (DLI) levels ranging from 45–50 mol·m−2·d−1 in summer and contrasting with 0–5 mol·m−2·d−1 during winter. To compensate, growth room cultivation that is independent of outdoor conditions could be used in winter. Depending on the efficacy of the lamps, the electricity required for sole-source lighting at an intensity of 300 µmol·m−2·s−1 for 16 h would be between 1.4 and 2.4 kWh·m−2·d−1. Greenhouses with supplementary lighting could help start the cultivation earlier in spring and extend it further into autumn. The energy required for lighting highly depends on several factors such as the natural light transmittance, the light threshold settings, and the lighting control protocol, resulting in electric demands between 0.6 and 2.4 kWh·m−2·d−1. Integrating PV on the roof or wall structures of the greenhouse could offset some of this electricity, with specific energy yields ranging from 400 to 1120 kWh·kW−1·yr−1 depending on the region and system design.

Underwater Light Characteristics of Turbid Coral Reefs of the Inner Central Great Barrier Reef

Hyper-spectral and multi-spectral light sensors were used to examine the effects of elevated suspended sediment concentration (SSC) on the quantity and quality (spectral changes) of underwater downwelling irradiance in the turbid-zone coral reef communities of the inner, central Great Barrier Reef (GBR). Under elevated SSCs the shorter blue wavelengths were preferentially attenuated which together with attenuation of longer red wavelengths by pure water shifted the peak in the underwater irradiance spectrum ~100 nm to the less photosynthetically useful green-yellow waveband (peaking at ~575 nm). The spectral changes were attributed to mineral and detrital content of the terrestrially-derived coastal sediments as opposed to chromophoric (coloured) dissolved organic matter (CDOM). A simple blue to green (B/G, λ455:555 nm) ratio was shown to be useful in detecting sediment (turbidity) related decreases in underwater light as opposed to those associated with clouds which acted as neutral density filters. From a series of vertical profiles through turbid water, a simple, multiple component empirical optical model was developed that could accurately predict the light reduction and associated spectral changes as a function of SSC and water depth for a turbid-zone coral reef community of the inner GBR. The relationship was used to assess the response of a light sensitive coral, Pocillopora verrucosa in a 28-d exposure laboratory-based exposure study to a daily light integral of 1 or 6 mol quanta m2. PAR with either a broad spectrum or a green-yellow shifted spectrum. Light reduction resulted in a loss of the algal symbionts (zooxanthellae) of the corals (bleaching) and significant reduction in growth and lipid content. The 6 mol quanta m2 d−1 PAR treatment with a green-yellow spectrum also resulted in a reduction in the algal density, Chl a content per cm2, lipids and growth compared to the same PAR daily light integral under a broad spectrum. Turbid zone coral reef communities are naturally light limited and given the frequency of sediment resuspension events that occur, spectral shifts are a common and previously unrecognised circumstance. Dedicated underwater light monitoring programs and further assessment of the spectral shifts by suspended sediments are essential for contextualising and further understanding the risk of enhanced sediment run-off to the inshore turbid water communities.

Morphological and Physiological Properties of Greenhouse-Grown Cucumber Seedlings as Influenced by Supplementary Light-Emitting Diodes with Same Daily Light Integral

Insufficient light in autumn–winter may prolong the production periods and reduce the quality of plug seedlings grown in greenhouses. Additionally, there is no optimal protocol for supplementary light strategies when providing the same amount of light for plug seedling production. This study was conducted to determine the influences of combinations of supplementary light intensity and light duration with the same daily light integral (DLI) on the morphological and physiological properties of cucumber seedlings (Cucumis sativus L. cv. Tianjiao No. 5) grown in a greenhouse. A supplementary light with the same DLI of 6.0 mol m−2 d−1 was applied with the light duration set to 6, 8, 10, or 12 h d−1 provided by light-emitting diodes (LEDs), and cucumber seedlings grown with sunlight only were set as the control. The results indicated that increasing DLI using supplementary light promoted the growth and development of cucumber seedlings over those grown without supplementary light; however, opposite trends were observed in the superoxide dismutase (SOD) and catalase (CAT) activities. Under equal DLI, increasing the supplementary light duration from 6 to 10 h d−1 increased the root surface area (66.8%), shoot dry weight (24.0%), seedling quality index (237.0%), root activity (60.0%), and stem firmness (27.2%) of the cucumber seedlings. The specific leaf area of the cucumber seedlings decreased quadratically with an increase in supplementary light duration, and an opposite trend was exhibited for the stem diameter of the cucumber seedlings. In summary, increased DLI or longer light duration combined with lower light intensity with equal DLI provided by supplementary light in insufficient sunlight seasons improved the quality of the cucumber seedlings through the modification of the root architecture and stem firmness, increasing the mechanical strength of the cucumber seedlings for transplanting.

Enabling Year-round Cultivation in the Nordics - Agrivoltaics and Adaptive LED Lighting Control of Daily Light Integral

High efficacy LED lamps combined with adaptive lighting control and greenhouse integrated photovoltaics (PV) could enable the concept of year-round cultivation and become a feasible option even in the harsh climate of the Nordic countries. Meteorological satellite data of this region was analyzed in a parametric study to evaluate the potential of these technologies. The generated maps showed monthly average temperatures fluctuating from -20°C to 20°C throughout the year. The natural photoperiod and light intensity also changed drastically, resulting in monthly average daily light integral (DLI) levels ranging from 45-50 mol·m-2·d-1 in summer and contrasting with 0-5 mol·m-2·d-1 during winter. To compensate, growth room cultivation independent from outdoor conditions could be used in winter. Depending on the efficacy of the lamps, the electricity required for sole-source lighting at 300 µmol·m-2·s-1 for 16 hours would be between 1.4 and 2.4 kWh·m-2·d-1. Greenhouses with supplementary lighting could help start the cultivation earlier in spring and extend it further into autumn. The energy required for lighting highly depends on several factors such as the natural light transmittance, the light threshold settings and the lighting control protocol, resulting in electric demands between 0.6 and 2.4 kWh·m-2·d-1. Integrating PV on the roof or wall structures of the greenhouse could offset some of this electricity, with specific energy yields ranging from 400 to 1120 kWh·kWp-2·yr-1 depending on the region and system design.

Effect of daily light integral treatments on free amino acids and sugars contributing flavor and acrylamide formation in potato tubers of Solanum tuberosum L.

To study the effect of photoperiodic conditions on the chemical composition of potato tubers, seven cultivars, grown under controlled conditions, were evaluated for the content of free amino acids (FAA) and sugars. The differences in these compounds may have an effect on the susceptibility of acrylamide formation during potato processing as well as on the flavor profile of potato products. Tubers were produced in growth chambers under two artificially induced photoperiods; 8 h light and 15 h light per day, resulting in conditions with two different daily light integral (DLI) levels. The photoperiodic treatments influenced the total FAA and free sugar contents and composition. Of the analyzed 19 FAAs, the concentrations of 14 FAAs were significantly lower in tubers exposed to the 15 h light period compared to 8 h light, whereas the glucose content was significantly higher. The total FAA concentrations were 15–46% lower and the glucose concentrations 6–64% higher in the seven cultivars exposed to the 15 h light conditions than in those grown in 8 h light.

Modeling growth and development of hydroponically grown dill, parsley, and watercress in response to photosynthetic daily light integral and mean daily temperature

In controlled environments, crop models that incorporate environmental factors can be developed to optimize growth and development as well as conduct cost and/or resource use benefit analyses. The overall objective of this study was to model growth and development of dill ‘Bouquet’ (Anethum graveolens), parsley ‘Giant of Italy’ (Petroselinum crispum), and watercress (Nasturtium officinale) in response to photosynthetic daily light integral (DLI) and mean daily temperature (MDT). Plants were grown hydroponically in five greenhouse compartments with MDTs ranging from 9.7 to 27.2 °C under 0%, 30%, or 50% shade cloth to create DLIs ranging from 6.2 to 16.9 mol·m‒2·d‒1. MDT and DLI interacted to influence dill fresh mass and height, and watercress maximum quantum yield of dark adapted leaves (Fv/Fm), height, and branch number while only MDT affected dill leaf number and watercress fresh mass and branch length. Besides dry matter concentration (DMC), parsley was influenced by MDT and not DLI. Increasing MDT from ≈10 to 22.4 °C (parsley) or 27.2 °C (dill and watercress), linearly or near-linearly increased fresh mass. For dill, increasing DLI decreased fresh mass when MDT was low (9.7 to 13.9 °C) and increased fresh mass when MDT was high (18.4 to 27.2 °C). DMC of dill, parsley, and watercress increased as MDT decreased or DLI increased, indicating a higher proportion of plant fresh mass is water at higher MDTs or lower DLIs. With these data we have created growth and development models for culinary herbs to aid in predicting responses to DLI and MDT.