Average Photosynthetic Photon Flux Density Research Articles

Physiological changes underlying increased photosynthetic-nitrogen use efficiency in response to low-nitrogen conditions in Brassica napus L

The photosynthetic-nitrogen use efficiency (PNUE) of Brassica napus L. is reported to increase under low nitrogen (N) condition. However, the underlying physiological mechanisms are unclear. In this study, the physiological mechanisms underlying increase in the photosynthetic-nitrogen use efficiency of Brassica napus L. under low-nitrogen condition were investigated by assessing the changes in plant architecture, light reception, nitrogen allocation, and leaf tissue structure. The plants exhibited dwarf, upright, and compact phenotype under low-nitrogen condition. Although the total photons received by plants decreased, the average photosynthetic photon flux density remained unchanged. The nitrogen photon reception efficiency (NPRE, calculated as total photons/N accumulation in leaves) was significantly increased by 76.61%–100.63%. The proportion of nitrogen allocated for photosynthesis was increased by 22.06%–38.86%. Moreover, although the leaf thickness remained unchanged, the epidermal thickness increased, and the spongy tissues became thinner. The density of mesophyll cells and chloroplasts significantly increased. Low-nitrogen condition significantly decreased the resistance to CO2 transport and significantly increased stomatal conductance (gs), intercellular carbon dioxide concentration (Ci), mesophyll conductance (gm), and CO2 concentration in chloroplasts (Cc). Correlation analysis revealed that light reception, nitrogen allocation in the leaves, and leaf tissue structure were significantly correlated with PNUE. Random forest analysis revealed that nitrogen photon reception efficiency and storage nitrogen were the primary factors positively and negatively impacting photosynthetic-nitrogen use efficiency, respectively. This study enhanced the understanding of the physiological mechanism of increased PNUE of B. napus under low-nitrogen condition.

Investigating pulsed LED effectiveness as an alternative to continuous LED through morpho-physiological evaluation of baby leaf lettuce (Lactuca sativa L. var. Acephala)

Photoperiod, light intensity, and spectral quantum distribution (SPD) affect plant development and physiology. Light determines morphological signals, influences plant behavior and regulates metabolism in addition to providing energy for photosynthesis. In this experiment, lettuce (Lactuca sativa) was grown in an indoor LED-equipped chamber, operated in a pulsed and continuous mode, with an average photosynthetic photon flux density (PPFD) at a seedling level of 150 µmole s¯¹ m¯², photoperiod of 16 h for growing cycle of 30 days. The primary aim of this study was to observe the effects of varying LED on the growth and quality of the produce. Regardless of the treatments, in both continuous and pulsed LED, an increment in the yield, leaf length and leaf width of lettuce was recorded in comparison to the control, which was managed in a glasshouse under controlled environmental conditions using a winter cropping cycle. In-vitro physiological analysis of lettuce revealed the outperformance of the continuous LED treatment over the pulsed LED as well as the control in terms of total sugars, chlorophyll concentration, carotenoids, phenolic index, and sucrose accumulation. Continuous LED treatment has also resulted in a significant reduction in nitrate content, a commercially vital parameter, making it the most advantageous and effective of all the treatments performed. However, the production of anthocyanins, an antioxidant released during stress, was enhanced under pulsed LED which requires further investigation and improvements to achieve an improved metabolite profile of lettuce with a minimal energy usage and cost.

Involvement of sugar and abscisic acid in the genotype-specific response of rose to far-red light.

Plant architecture determines yield (fruit or flowers) and product quality in many horticultural species. It results from growth and branching processes and is dependent on genetic and environmental factors such as light quality. Highly significant genotype and light quality effects and their interaction have been demonstrated on the architecture of rose. Far-red (FR) light is known for its favourable effect on plant growth and development. We evaluated the effect of FR on rose growth and development and its interaction with the genotype through architectural, eco-physiological (net photosynthesis rate) and biochemical (sugar and hormone concentrations) approaches. Two cultivars (‘The Fairy’ – TF – and Knock Out® Radrazz – KO) with contrasting architectures were grown in a climate chamber under FR or in the absence of FR at an average photosynthetic photon flux density (400–700 nm) of 181.7 ± 12.8 μmol m−2 s−1 for 16 h. A significant effect of FR on the architecture of TF was demonstrated, marked by greater stem elongation, shoot branching and flowering, while KO remained insensitive to FR, supporting a genotype x FR interaction. The response of TF to FR was associated with improved photosynthetic capabilities, while KO exhibited an elevated level of abscisic acid (ABA) in its leaves. FR-dependent ABA accumulation might inhibit photosynthesis and prevent the increased plant carbon status required for growth. From a practical perspective, these findings argue in favour of a better reasoning of the choice of the cultivars grown in lighted production systems. Further investigations will be necessary to better understand these genotype-specific responses to FR and to unravel their molecular determinants.

Estimating Light Acclimation Parameters of Cucumber Leaves Using Time-Weighted Averages of Daily Photosynthetic Photon Flux Density.

Leaves acclimate to day-to-day fluctuating levels of photosynthetic photon flux density (PPFD) by adjusting their morphological and physiological parameters. Accurate estimation of these parameters under day-to-day fluctuating PPFD conditions benefits crop growth modeling and light environment management in greenhouses, although it remains challenging. We quantified the relationships between day-to-day PPFD changes over 6 days and light acclimation parameters for cucumber seedling leaves, including leaf mass per area (LMA), chlorophyll (Chl) a/b ratio, maximum net photosynthetic rate (Pnmax), maximum rate of ribulose-1,5-bisphosphate (RuBP) carboxylase/oxygenase (Vcmax), and maximum rate of electron transport (Jmax). The last two parameters reflect the capacity of the photosynthetic partial reactions. We built linear regression models of these parameters based on average or time-weighted averages of daily PPFDs. For time-weighted averages of daily PPFDs, the influence of daily PPFD was given a specific weight. We employed three types of functions to calculate this weight, including linear, quadratic, and sigmoid derivative types. We then determined the trend of weights that estimated each parameter most accurately. Moreover, we introduced saturating functions to calibrate the average or time-weighted averages of daily PPFDs, considering that light acclimation parameters are usually saturated under high PPFDs. We found that time-weighted average PPFDs, in which recent PPFD levels had larger weights than earlier levels, better estimated LMA than average PPFDs. This suggests that recent PPFDs contribute more to LMA than earlier PPFDs. Except for the Chl a/b ratio, the average PPFDs estimated Pnmax, Vcmax, and Jmax with acceptable accuracy. In contrast, time-weighted averages of daily PPFDs did not improve the estimation accuracy of these four parameters, possibly due to their low response rates and plasticity. Calibrating functions generally improved estimation of Chl a/b ratio, Vcmax, and Jmax because of their saturating tendencies under high PPFDs. Our findings provide a reasonable approach to quantifying the extent to which the leaves acclimate to day-to-day fluctuating PPFDs, especially the extent of LMA.

Blue Light Monochromatic Irradiation for 12 Hours in Lighting Pattern with Combinations of Blue and Red Light Elongates Young Cos Lettuce Leaves and Promotes Growth under High Daily Light Integral

Cos lettuce was grown under different spectral photon flux density distribution (SPFD) change patterns with blue- and/or red light-emitting diode (LED) irradiation with a 24-hour cycle. Twelve treatments were designed with a combination of four relative SPFD (RSPFD) change patterns and three photosynthetic photon flux density (PPFD) levels. The RSPFD change patterns were as follows: BR/BR, simultaneous blue- and red-light irradiation (BR) for 24 h; R/BR, red-light monochromatic irradiation (R) for 12 h followed by 12 hours of BR; B/BR, blue-light monochromatic irradiation (B) for 12 hours followed by 12 hours of BR; and B/R, 12 hours of B followed by 12 hours of R. Each RSPFD change pattern was conducted at three daily average photosynthetic photon flux densities (PPFDave) of 50, 100, and 200 µmol·m−2·s−1. The RSPFD change patterns that included B (B/BR and B/R) resulted in elongated leaves. A low ratio of active phytochrome to total phytochrome under B was considered the reason for leaf elongation. Shoot dry weight was significantly greater under the RSPFD change patterns that included B when the PPFDave was 200 µmol·m−2·s−1. The leaf elongation caused by B would have increased the amount of light received and thereby promoted growth. However, excessive leaf elongation caused the plants to fall, and growth was not promoted under the RSPFD change patterns that included B when the PPFDave was 50 µmol·m−2·s−1. Thus, 12-hour B promoted growth under conditions in which leaf elongation leads to increases in the amount of light received.

Effect of a photoselective filter on the yield and postharvest quality of 'Viroflay' baby spinach (Spinacia oleracea L.) leaves cultivated in a hydroponic system

Consumers are demanding foods with high sensory and nutritional quality including a higher content of compounds that help maintain good health. Given this scenario, new technologies are emerging to produce fresh salads that have the characteristics currently in demand. Shade nettings or photoselective filters on fruit and vegetable crops are a technology that provides protection, modifies the light spectrum resulting in a higher accumulation of antioxidant compounds, making them more desirable to consumers. The objective of this study was to compare the effect of shade netting on the fresh quality parameters of baby leaf spinach grown in a hydroponic system at harvest and after a period of 10 days at 4 °C. By using different shade netting colors, the average photosynthetic photon flux density (PPFD) that reaches the plants was modified during the growing period of baby leaf spinach (red: 118.35 μmol m−2 s−1; blue:117.96 μmol m−2 s−1; gray: 63.18 μmol m−2 s−1 and control without shade nettings: 278.12 μmol m−2 s−1). At harvest, baby leaf spinach grown under the red shade netting reached the highest yield. However, with the blue filter, leaves showed a value of 9.3 % dry weight, significantly higher than the values from red and gray filters with values of 7.3 and 6.3 %, respectively. The phenolic compound contents reached significantly higher values of 485.5 mg gallic acid equivalent (GAE) per 100 g−1 FW for the baby leaf spinach grown under the red filter compared to the blue, gray and control filters with values of 472.5; 387.6 and 316.5 mg GAE per 100 g−1 FW, respectively. The antioxidant capacity was significantly higher under the red filter. The sensory quality parameters indicated that spinach grown under color filters did not show off-flavors and maintained its turgidity and appearance at harvest. In the postharvest period, baby leaf spinach grown under red filter maintained the highest total phenol content and antioxidant activity after 10 days at 4 °C with similar appearance and turgidity as the control.

Global evidence for the acclimation of ecosystem photosynthesis to light.

Photosynthesis responds quickly to changes in light, increasing with incoming photosynthetic photon flux density (PPFD) until the leaves become light saturated. This instantaneous response to PPFD, which is widely studied and incorporated into models of photosynthesis, is overlaid on non-instantaneous photosynthetic changes resulting from the acclimation of plants to average PPFD over intermediate timescales of a week to months [Formula: see text]. Such photosynthetic light acclimation is not typically incorporated into models, due to the lack of observational constraints. Here, we use eddy covariance observations from globally distributed and automated sensor networks, along with photosynthesis estimates from nine terrestrial biosphere models (TBMs), to quantify and assess photosynthetic acclimation to light in natural environments. We also use recent theoretical developments to incorporate light acclimation in a TBM. Our results show widespread light acclimation of ecosystem photosynthesis. On average, a 1 μmol m-2 s-1 increase in [Formula: see text] (ten-day average PPFD) leads to a 0.031 ± 0.013 μmol C m-2 s-1 increase in the maximum photosynthetic assimilation rate (Amax), with croplands having stronger acclimation rates than grasslands and forests. Our analysis shows that the TBMs examined either neglect or substantially underestimate light acclimation. By updating a TBM to include photosynthetic acclimation, successfully reproducing the [Formula: see text]-Amax relationship, we provide a robust method for the incorporation of photosynthetic light acclimation in future models.

Longer Photoperiods with Adaptive Lighting Control Can Improve Growth of Greenhouse-grown ‘Little Gem’ Lettuce (Lactuca sativa)

Supplemental lighting can improve the growth of greenhouse crops, but the electricity required for supplemental lighting can be a significant expense for greenhouse growers. Lighting control strategies that use the dimmability of light-emitting diodes (LEDs) have the potential to decrease this cost. In our experiments, we tested the hypothesis that providing ‘Little Gem’ lettuce (Lactuca sativa) plants with the same daily amount of light, spread out over a longer photoperiod and at lower average photosynthetic photon flux densities (PPFDs), would improve growth because light is used more efficiently to drive photosynthesis at lower PPFDs. We conducted two greenhouse experiments wherein supplemental light was provided to reach a minimum daily light integral (DLI) of 17 mol·m−2·d−1 with a 12, 15, 18, or 21-hour photoperiod using adaptive lighting control of LED lights. As the photoperiod for supplemental lighting was increased and supplemental light was provided at lower average PPFDs, plant dry weight increased. Conversion efficiency, the estimated increase in dry weight per Joule expended on supplemental lighting, increased as the photoperiod was extended from 12 to 21 hours. Leaf size and chlorophyll content index increased with longer photoperiods. The number of plants with symptoms of tipburn, including apical and marginal necrosis, also increased as the photoperiod was extended. These results demonstrate that adaptive lighting control can be used to increase the growth of ‘Little Gem’ lettuce and the energy use efficiency of supplemental lighting by providing supplemental light at relatively low PPFDs.

Nitrate accumulation, productivity and photosynthesis of Brassica alboglabra grown under low light with supplemental LED lighting in the tropical greenhouse

Vegetables are a large source of nitrate (NO3−) in our diet. As NO2− is toxic to humans, it is undesirable to consume vegetables with high NO3− content. Therefore, this study aimed to investigate the effect of supplementing of red- and blue-LED lighting to B. alboglabra grown in the tropical greenhouse in terms of moderating NO3− accumulation, improving photosynthesis, and enhancing productivity. All plants were grown hydroponically in full nutrients under prevailing greenhouse conditions for 20 days (full sunlight). Thereafter, plants were subjected to three different light treatments for 12 days: full sunlight, shade, and shade supplemented with LEDs. The average midday photosynthetic photon flux density (PPFD) during the light treatment periods were 220 μmol m−2 s−1 (full sunlight), 55 μmol m−2 s−1 (shade), and 220 μmol m−2 s−1 (shade supplemented with LEDs). Shoot nitrate (NO3−) concentration increased significantly in plants grown in the shade. However, shoot NO3− concentration was reduced when plants were supplemented with red- and blue-LED lighting. Photosynthetic CO2 assimilation, stomatal conductance, and productivity also improved in these plants. Our results suggest that supplemental red- and blue-LED lighting in a tropical greenhouse during periods of cloudy and hazy weather could improve productivity and nutrient quality of Chinese broccoli.

Diurnal Changes in Leaf Photochemical Reflectance Index in Two Evergreen Forest Canopies

The spectral properties of plant leaves relate to the state of their photosynthetic apparatus and the surrounding environment. An example is the well known photosynthetic downregulation, active on the time scale from minutes to hours, caused by reversible changes in the xanthophyll cycle pigments. These changes affect leaf spectral absorption and are frequently quantified using the photochemical reflectance index (PRI). This index can be used to remotely monitor the photosynthetic status of vegetation, and allows for a global satellite-based measurement of photosynthesis. Such earth observation satellites in near-polar orbits usually cover the same geographical location at the same local solar time at regular intervals. To facilitate the interpretation of these instantaneous remote PRI measurements and upscale them temporally, we measured the daily course of leaf PRI in two evergreen biomes—a European boreal forest and an Amazon rainforest. The daily course of PRI was different for the two locations: At the Amazonian forest, the PRI of Manilkara elata leaves was correlated with the average photosynthetic photon flux density (PPFD) ( $R^{2}=0.59$ , $p ) of the 40 minutes preceding the leaf measurement. In the boreal location, the variations in Pinus sylvestris needle PRI were only weakly ( $R^{2}=0.27$ , $p ) correlated with mean PPFD of the preceding two hours; for Betula pendula , the correlation was insignificant ( $p>0.5)$ regardless of the averaging period. The measured daily PRI curves were specific to species and/or environmental conditions. Hence, for a proper interpretation of satellite-measured instantaneous photosynthesis, the scaling of PRI measurements should be supported with information on its correlation with PPFD.

Effects of photosynthetic photon flux density, frequency, duty ratio, and their interactions on net photosynthetic rate of cos lettuce leaves under pulsed light: explanation based on photosynthetic-intermediate pool dynamics.

Square-wave pulsed light is characterized by three parameters, namely average photosynthetic photon flux density (PPFD), pulsed-light frequency, and duty ratio (the ratio of light-period duration to that of the light-dark cycle). In addition, the light-period PPFD is determined by the averaged PPFD and duty ratio. We investigated the effects of these parameters and their interactions on net photosynthetic rate (P n) of cos lettuce leaves for every combination of parameters. Averaged PPFD values were 0-500µmolm-2s-1. Frequency values were 0.1-1000Hz. White LED arrays were used as the light source. Every parameter affected P n and interactions between parameters were observed for all combinations. The P n under pulsed light was lower than that measured under continuous light of the same averaged PPFD, and this difference was enhanced with decreasing frequency and increasing light-period PPFD. A mechanistic model was constructed to estimate the amount of stored photosynthetic intermediates over time under pulsed light. The results indicated that all effects of parameters and their interactions on P n were explainable by consideration of the dynamics of accumulation and consumption of photosynthetic intermediates.

Impact of Carbon Dioxide and Increasing Nitrogen Levels on Growth, Photosynthetic Capacity, Carbohydrates and Secondary Metabolites in Kacip Fatimah (Labisia pumila)

Aims: This study was designed to investigate how CO2 and nitrogen availability alters growth, leaf gas exchange, primary and secondary metabolites production (total phenolics and flavonoid) in three varieties of L. pumila. namely var alata, var pumila and var lanceolata. under CO2 enrichment (1200 µmol mol-1) combined with four levels of nitrogen fertilization (0, 90, 180 and 270 kg N ha-1) for 15 weeks. Study Design: Three-month old L. pumila seedlings of var. alata, var. pumila and var. lanceolata were left for a month to acclimatize in a nursery until ready for the treatments. Carbon dioxide enrichment treatment started when the seedlings reached 4 months old where plants were exposed to 1200 µmol-1 mol-1 CO2 and fertilized with four levels of nitrogen concentrations viz. 0, 90, 180 and 270 kg N Ha-1. The fertilization with nitrogen levels were split into three applications. A control at ambient CO2 (400 µmol-1 mol-1) with standard N fertilization (180 kg N ha-1) was included to compare plant responses to high CO2 combined with different levels of N. Place and Duration of Study: Faculty of Agriculture Glasshouse Complex, Universiti Putra Malaysia from February to May 2011. Methodology: The seedlings were raised in specially constructed growth houses receiving 12-h photoperiod and average photosynthetic photon flux density of 300 µmol m-2 s-1. Carbon dioxide at 99.8% purity was supplied from a high–pressure CO2 cylinder and injected through a pressure regulator into fully sealed 2 m x 3 m growth houses at 2-h daily and applied continuous from 800 to 1000. Total plant biomass was taken by calculating the dry weight of root, stem and leaf per seedling. Total leaf area per plant was measured using a leaf area meter (LI-3100, Lincoln Inc, USA). The measurement of photosynthesis was obtained from a closed system of infra-red gas analyzer LICOR 6400 Portable Photosynthesis System. The response of net CO2 exchange (A) to changing intercellular CO2 concentration (Ci) was conducted at 27°C, 50% relative humidity and at light saturating conditions of 800 µmol m-2s-1. Anthrone method was used to determine the content of total available carbohydrate. Follin–Ciocalteau reagent was used to determine total phenolics and flavonoid using spectrophotometer. Results: In all parameters measured there were no significant was observed in the three varieties. As the levels of nitrogen increased from 0 to 270 kg N ha-1, plant growth, photosynthesis and total chlorophyll content was enhanced. However, carbohydrate, total phenolics and flavonoid was reduced with the increase in nitrogen fertilization. It was found that the high application of nitrogen can increased the photosynthetic capacity of L. pumila by having high Vcmax (RuBisCO CO2 fixation capacity), A sat (CO2 saturation point) and low dark respiration rate in the analysis of A/Ci curves. The production of secondary metabolites was related to increased total non-structural carbohydrate (TNC) under low nitrogen condition. Photosynthesis, displayed a significant negative relationship with secondary metabolites production. Total chlorophyll content exhibited very significant negative relationships with total soluble sugar, starch and total non-structural carbohydrate. Conclusion: This study demonstrated that enrichment with high levels of CO2 is able to enhance the production of plant secondary metabolites. However, increased nitrogen fertilization can reduce the production of these plant secondary metabolites under CO2 enrichment. When there were accumulation of TNC in plant leaves and reduction in photosynthesis, the production of plant secondary metabolites might be up-regulated. The increase in the production of plant secondary metabolites was indicated by reduction in chlorophyll contents.

Relationships between light environment and subsurface accumulation during the daytime in the red-tide dinoflagellate Karenia mikimotoi

Diurnal vertical migration of the red-tide dinoflagellate Karenia mikimotoi and environmental conditions were measured in Hiroshima Bay and the Yatsushiro Sea in July of 2012 and 2015, respectively. The uppermost daytime depths for K. mikimotoi were 1.3–6.0 m and did not correspond to the pycnocline; most cells reached the bottom each night. Although the incident photosynthetic photon flux density (PPFD) varied among days, average PPFDs at the mean cell distribution depths were similar (59–65 µmol m−2 s−1) between compensation and saturation PPFDs for photosynthesis. Total daily PPFD at the mean depth was between the growth threshold and that for maximum growth rates. Among visible wavelengths, the photon flux density of green and yellow light (500–600 nm) at the mean depth was major (about 61% of the total), and the PFD of blue (400–500 nm) was always relatively minor (about 20%). Laboratory results identified green light as sufficient for K. mikimotoi growth, yielding growth rates equivalent to those under blue light. This study suggests that the vertical cell distribution depth during the daytime is regulated by underwater light transmission and that green light is valuable for growth and photosynthesis of K. mikimotoi.

A kinetic model for estimating net photosynthetic rates of cos lettuce leaves under pulsed light.

Time-averaged net photosynthetic rate (P n) under pulsed light (PL) is known to be affected by the PL frequency and duty ratio, even though the time-averaged photosynthetic photon flux density (PPFD) is unchanged. This phenomenon can be explained by considering that photosynthetic intermediates (PIs) are pooled during light periods and then consumed by partial photosynthetic reactions during dark periods. In this study, we developed a kinetic model to estimate P n of cos lettuce (Lactuca sativa L. var. longifolia) leaves under PL based on the dynamics of the amount of pooled PIs. The model inputs are average PPFD, duty ratio, and frequency; the output is P n. The rates of both PI accumulation and consumption at a given moment are assumed to be dependent on the amount of pooled PIs at that point. Required model parameters and three explanatory variables (average PPFD, frequency, and duty ratio) were determined for the simulation using P n values under PL based on several combinations of the three variables. The model simulation for various PL levels with a wide range of time-averaged PPFDs, frequencies, and duty ratios further demonstrated that P n under PL with high frequencies and duty ratios was comparable to, but did not exceed, P n under continuous light, and also showed that P n under PL decreased as either frequency or duty ratio was decreased. The developed model can be used to estimate P n under various light environments where PPFD changes cyclically.

Light Apparatus for Mesocosm Photo‐manipulation (LAMP): An inexpensive waterproof lighting device for within‐lake mesocosm experiments

Although light is a key biological driver, light additions to in‐lake experiments can be difficult, if not impossible. To address this problem, we developed an inexpensive Lighting Apparatus for Mesocosm Photo‐manipulation (LAMP), a device that can be deployed within experimental underwater enclosures to increase ambient light levels. Each apparatus consists of 12 Light Emitting Diode (LED) flashlights embedded within a watertight PVC frame. Through the use of a voltage regulator, each is wired to a 12V deep‐cycle marine battery. Twelve LAMPs were deployed during a 3.5‐week mesocosm experiment in Cranberry Lake in the Adirondack region of New York State and run 12 hours per day. LAMPs proved durable under harsh wind and weather conditions. Mesocosms with LAMPs had significantly higher average Photosynthetic Photon Flux Density (PPFD) in the water column than did controls (8% higher integrated Photosynthetic Active Radiation [PAR] over a 1.75 m depth, paired t test, P < 0.01). Other potential research applications for LAMPs include (1) testing light limitation in highly eutrophic systems where algal biomass may be self‐shading, (2) experimentation at depth (e.g., examination of light limitation at the deep chlorophyll maximum), (3) application at different depths or in water bodies where specific wavelengths have been naturally attenuated using LEDs with different spectral properties, (4) testing animal responses to light climate in the field, or (5) collection of macroinvertebrates or fish larvae in modified LAMP‐based light traps.

Effects of Supplemental Lighting of High Pressure Sodium and Lighting Emitting Plasma on Growth and Productivity of Paprika during Low Radiation Period of Winter Season

본 연구는 겨울철 약광기 파프리카의 안정적 생산을 위한 보광 효과를 구명하고자 수행하였다. 보광 램프로는 고압나트륨(high pressure sodium, HPS)과 Lighting Emitting Plasma (LEP)를 이용하였다. 두 광원 램프로부터 수직으로 떨어진 거리가 증가함에 따라 광량자속밀도(PPFD)는 감소하였다. 동일 거리별 PPFD는 LEP 램프에서 HPS 램프보다 2배 정도 높았지만, 거리 증가에 따른 감소율은 HPS 램프에 비해 LEP 램프에서 상당히 높았다. 수직 거리 100cm 지점에서 횡으로의 거리에 따른 두 광원 간 PPFD 차이는 수직 거리에 따른 차이보다 적었다. 1월 동안 보광 처리에 따른 식물체 정단부의 PPFD 측정 결과, 무처리구에 비해 HPS 보광 처리구에서는 137%, LEP 보광 처리구에서는 315%로 보광에 따른 유효 광량은 뚜렷하게 증가하였다. 그러나 식물체 정단부의 온도는 큰 차이를 나타내지 않았다. 보광 처리 20주째까지 파프리카의 착화를 증가시키는 데에 효과가 나타나지 않았다. 엽장과 엽폭은 LEP 처리구에서 가장 길었고 광합성률도 가장 높았다. 수확과실의 무게는 무처리구에 비해 보광 처리구들에서 무거웠고, LEP 보광 처리는 과장과 과고를 증가시키는 데에 효과를 나타내었다. 3회에 걸쳐 수확된 과실수는 HPS 보광 처리구나 무처리구에 비해 LEP 보광 처리구에서 많았다. 따라서 겨울철 약광기 파프리카의 생육 및 생산성을 증대시키는 데에는 LEP 광원을 이용한 보광 효과가 인정되나, 차후 현장에 적합한 LEP 광원의 활용 방법에 대한 연구가 필요할 것으로 생각된다. This research was carried out to investigate the effect of supplemental lighting on stable productivity of paprika (Capsicum annuum L.) during low radiation period of winter season. The supplemental lighting sources used in this research were high pressure sodium (HPS) and lighting emitting plasma (LEP). Photosynthetic photon flux density (PPFD) emitted from both lamps decreased as vertical distance from lamp increased. The PPFD of LEP lamps were twice more than that of the HPS lamp per unit distance, but the rate of decreased PPFD of t he LEP per unit distance was higher than that of HPS lamp. And different degrees of PPFD between HPS and LEP lamps by horizontal distance had a smaller degree of difference than by vertical distance at the 100 cm away point. As daily average PPFD measured at the top of the plant under the supplemental lighting during January, the supplemental lighting significantly increased radiation. Radiation of HPS and LEP lighting was 137% and 315% higher than control (without supplemental lighting = sunlight). Air temperature in the top of the plant was not significant different among treatments. HPS and LEP lighting had no effect on increase of flower settings. Leaf length and width with LEP lighting was the longest, photosynthetic was higher than those of other treatments. Supplemental lighting treatments significant increased fruit length and diameter. Especially LEP lighting treatment had a greater effect on fruit length and diameter. In conclusion, LEP lighting treatment during low radiation period greatly affected growth and production of paprika. Further research will be required for the suitable application of LEP lighting in paprika production.

Measurement System of Photosynthetic Photon Flux Distribution and Illumination Efficiency of LED Lamps for Plant Growth

Purpose: This study was conducted to develop a measurement system for determining photosynthetic photon flux (PPF) distribution and illumination efficiency of LED lamps. Methods: The system was composed of a linear moving sensor part (LMSP), a rotating part to turn the LMSP, a body assembly to support the rotating part, and a motor controller. The average PPF of the LED lamp with natural cooling and water cooling was evaluated using the measurement system. Results: The PPF of LED lamp with water cooling was 3.1-31.7% greater than that with natural cooling. Based on the measured value, PPF on the horizontal surface was predicted. Illumination efficiency of the LED lamp was slightly increased with water cooling by 3.4%, compared with natural cooling. A simulation program using MATLAB was developed to analyze the effects of the vertical distance from lighting sources to growing bed, lamp spacing, and number of LED lamps, on the PPF distribution on the horizontal surface. The uniformity of the PPF distribution of the LED lamps was fairly improved with 15 cm spacing, as compared to the 5 cm spacing. By simulation, PPF of 217.0±27.9umol m-2 s-1 was obtained at the vertical distance of 40 cm from six LED lamps with 12 cm spacing. This simulated PPF was compared to the measured one of 225.9±25.6umol m-2 s-1. After continuous lighting of 346 days, the relative PPF of LED lamps with water cooling and natural cooling was decreased by 6.6% and 22.8%, respectively, Conclusions: From these results, it was concluded that the measurement system developed in this study was useful for determining PPF and illumination efficiency of artificial lighting sources including LED lamp.

Plant lighting system with five wavelength-band light-emitting diodes providing photon flux density and mixing ratio control

BackgroundPlant growth and development depend on the availability of light. Lighting systems therefore play crucial roles in plant studies. Recent advancements of light-emitting diode (LED) technologies provide abundant opportunities to study various plant light responses. The LED merits include solidity, longevity, small element volume, radiant flux controllability, and monochromaticity. To apply these merits in plant light response studies, a lighting system must provide precisely controlled light spectra that are useful for inducing various plant responses.ResultsWe have developed a plant lighting system that irradiated a 0.18 m2 area with a highly uniform distribution of photon flux density (PFD). The average photosynthetic PFD (PPFD) in the irradiated area was 438 micro-mol m–2 s–1 (coefficient of variation 9.6%), which is appropriate for growing leafy vegetables. The irradiated light includes violet, blue, orange-red, red, and far-red wavelength bands created by LEDs of five types. The PFD and mixing ratio of the five wavelength-band lights are controllable using a computer and drive circuits. The phototropic response of oat coleoptiles was investigated to evaluate plant sensitivity to the light control quality of the lighting system. Oat coleoptiles irradiated for 23 h with a uniformly distributed spectral PFD (SPFD) of 1 micro-mol m–2 s–1 nm–1 at every peak wavelength (405, 460, 630, 660, and 735 nm) grew almost straight upwards. When they were irradiated with an SPFD gradient of blue light (460 nm peak wavelength), the coleoptiles showed a phototropic curvature in the direction of the greater SPFD of blue light. The greater SPFD gradient induced the greater curvature of coleoptiles. The relation between the phototropic curvature (deg) and the blue-light SPFD gradient (micro-mol m–2 s–1 nm–1 m–1) was 2 deg per 1 micro-mol m–2 s–1 nm–1 m–1.ConclusionsThe plant lighting system, with a computer with a graphical user interface program, can control the PFD and mixing ratios of five wavelength-band lights. A highly uniform PFD distribution was achieved, although an intentionally distorted PFD gradient was also created. Phototropic responses of oat coleoptiles to the blue light gradient demonstrated the merit of fine controllability of this plant lighting system.

Eight years of carbon dioxide exchange above a mixed forest at Borden, Ontario

This paper summarizes results from 8 years (1996–2003) of eddy covariance-based ecosystem CO 2 exchange measurements at the Borden Forest Research Station (44°19′N, 79°56′W). The site represents a mid-latitude, 100-year-old, mixed deciduous and coniferous forest dominated by red maple, aspen and white pine. The years 1996 and 1997 were relatively cold, had a late spring and received below average photosynthetic photon flux density (PPFD). This contrasts with an early spring, warmer soil and air temperatures during 1998–1999, and with distinctly wet year of 2000 and dry years of 2001–2003. The combination of early spring, warmer air and soil temperature and relatively high level of PPFD was associated with higher net ecosystem productivity (NEP) that peaked during 1999. Photosynthetic capacity was reduced and NEP showed a mid-growing season depression during the dry years of 2001–2003. Annual average ecosystem respiration (R) determined from a light response model was ∼30% less than R derived from a logistic respiration equation, relating night time CO 2 flux and soil temperature. However these independently determined R values were well correlated indicating that the site is unaffected by fetch and spatial heterogeneity problems. Based on the combined 8 years of growing season daytime data, an air temperature of 20–25 °C and a vapor pressure deficit (VPD) of 1.3 kPa were found to be the optimal conditions for CO 2 uptake by the canopy. Over the 1996–2003 period, the forest sequestered carbon at an average rate of 140 ± 111 gC m −2 y −1. The corresponding gross ecosystem photosynthesis (GEP) and R over this period were 1116 ± 93 gC m −2 y −1 and 976 ± 68 gC m −2 y −1, respectively. The annual carbon sequestration ranged from 19 gC m −2 in 1996 to 281 gC m −2 in 1999. However, these estimates were sensitive to frictional velocity threshold ( u * TH ) used for screening data associated with poor turbulent mixing at night. Increasing u * TH from 0.2 m s −1 (based on the inflection point in the nighttime CO 2 flux vs. u * relationship) to 0.35 m s −1 (determined using a u * TH selection algorithm based on change-point detection) modified the 8-year mean NEP estimate from 140 ± 111 gC m −2 y −1 to 65 ± 120 gC m −2 y −1. Both approaches show that the Borden forest was a low to moderate sink of carbon over the 8-year period.

Developing strategies for automated remote plant production systems: Environmental control and monitoring of the Arthur Clarke Mars Greenhouse in the Canadian High Arctic

The Arthur Clarke Mars Greenhouse is a unique research facility dedicated to the study of greenhouse engineering and autonomous functionality under extreme operational conditions, in preparation for extraterrestrial biologically-based life support systems. The Arthur Clarke Mars Greenhouse is located at the Haughton Mars Project Research Station on Devon Island in the Canadian High Arctic. The greenhouse has been operational since 2002. Over recent years the greenhouse has served as a controlled environment facility for conducting scientific and operationally relevant plant growth investigations in an extreme environment. Since 2005 the greenhouse has seen the deployment of a refined nutrient control system, an improved imaging system capable of remote assessment of basic plant health parameters, more robust communication and power systems as well as the implementation of a distributed data acquisition system. Though several other Arctic greenhouses exist, the Arthur Clarke Mars Greenhouse is distinct in that the focus is on autonomous operation as opposed to strictly plant production. Remote control and autonomous operational experience has applications both terrestrially in production greenhouses and extraterrestrially where future long duration Moon/Mars missions will utilize biological life support systems to close the air, food and water loops. Minimizing crew time is an important goal for any space-based system. The experience gained through the remote operation of the Arthur Clarke Mars Greenhouse is providing the experience necessary to optimize future plant production systems and minimize crew time requirements. Internal greenhouse environmental data shows that the fall growth season (July–September) provides an average photosynthetic photon flux of 161.09 μmol m −2 s −1 (August) and 76.76 μmol m −2 s −1 (September) with approximately a 24 h photoperiod. The spring growth season provides an average of 327.51 μmol m −2 s −1 (May) and 339.32 μmol m −2 s −1 (June) demonstrating that even at high latitudes adequate light is available for crop growth during 4–5 months of the year. The Canadian Space Agency Development Greenhouse [now operational] serves as a test-bed for evaluating new systems prior to deployment in the Arthur Clarke Mars Greenhouse. This greenhouse is also used as a venue for public outreach relating to biological life support research and its corresponding terrestrial spin-offs.