Optimal Light Intensity Research Articles

Sexual Difference in the Optimum Environmental Conditions for Growth and Maturation of the Brown Alga Undaria pinnatifida in the Gametophyte Stage.

Undaria pinnatifida is an annual brown kelp growing naturally in coastal areas as a major primary producer in temperate regions and is cultivated on an industrial scale. Kelps have a heteromorphic life cycle characterized by a macroscopic sporophyte and microscopic sexual gametophytes. The sex-dependent effects of different environmental factors on the growth and maturation characteristics of the gametophyte stage were investigated using response surface methodology. Gametophytes were taken from three sites in Japan: Iwate Prefecture, Tokushima Prefecture, and Kagoshima Prefecture in order to confirm the sexual differences in three independent lines. Optimum temperature and light intensity were higher for males (20.7–20.9 °C and 28.6–33.7 µmol m−2 s−1, respectively) than females (16.5–19.8 °C and 26.9–32.5 µmol m−2 s−1), and maturity progressed more quickly in males than females. Optimum wavelengths of light for growth and maturation of the gametophytes were observed for both blue (400–500 nm, λmax 453 nm) and green (500–600 nm; λmax 525 nm) lights and were sex-independent. These characteristics were consistent among the three regional lines. Slower growth optima and progress of maturation could be important for female gametophytes to restrict fertilization and sporophyte germination to the lower water temperatures of autumn and winter, and suggest that the female gametophyte may be more sensitive to temperature than the male. The sexual differences in sensitivity to environmental factors improved the synchronicity of sporeling production.

Influence of Medium Frequency Light/Dark Cycles on the Cultivation of Auxenochlorella pyrenoidosa

Light (wavelength, intensity, and light/dark cycle) have been considered as one of the most important parameters for microalgae cultivation. In this paper, the effect of medium frequency intermittent light on Auxenochlorella pyrenoidosa (formerly Chlorella pyrenoidosa) cultivation was investigated. Three parameters of intermittent light, light intensity, light/dark ratio, and light/dark cycle were employed and the influence of these parameters on the productivity of Auxenochlorella pyrenoidosa was studied. The biomass yield and growth rates were mainly affected by the light fraction and cycle time. Light with 220 μE m−2 s−1 light intensity was determined as the optimal light intensity for biomass production. At the light intensity of 420 μE m−2 s−1, the results indicated that the intermittent light improved the biomass production with larger light/dark ratio compared with the continuous light. At a lower mean light intensity over time, the intermittent light should be more suitable for biomass growth and the decrease in the light/dark ratio (L/D) will lead to a higher biomass productivity. The light/dark cycle time has little influence on the biomass yield.

Light and Primary Production Shape Bacterial Activity and Community Composition of Aerobic Anoxygenic Phototrophic Bacteria in a Microcosm Experiment.

Phytoplankton is a key component of aquatic microbial communities, and metabolic coupling between phytoplankton and bacteria determines the fate of dissolved organic carbon (DOC). Yet, the impact of primary production on bacterial activity and community composition remains largely unknown, as, for example, in the case of aerobic anoxygenic phototrophic (AAP) bacteria that utilize both phytoplankton-derived DOC and light as energy sources. Here, we studied how reduction of primary production in a natural freshwater community affects the bacterial community composition and its activity, focusing primarily on AAP bacteria. The bacterial respiration rate was the lowest when photosynthesis was reduced by direct inhibition of photosystem II and the highest in ambient light condition with no photosynthesis inhibition, suggesting that it was limited by carbon availability. However, bacterial assimilation rates of leucine and glucose were unaffected, indicating that increased bacterial growth efficiency (e.g., due to photoheterotrophy) can help to maintain overall bacterial production when low primary production limits DOC availability. Bacterial community composition was tightly linked to light intensity, mainly due to the increased relative abundance of light-dependent AAP bacteria. This notion shows that changes in bacterial community composition are not necessarily reflected by changes in bacterial production or growth and vice versa. Moreover, we demonstrated for the first time that light can directly affect bacterial community composition, a topic which has been neglected in studies of phytoplankton-bacteria interactions.IMPORTANCE Metabolic coupling between phytoplankton and bacteria determines the fate of dissolved organic carbon in aquatic environments, and yet how changes in the rate of primary production affect the bacterial activity and community composition remains understudied. Here, we experimentally limited the rate of primary production either by lowering light intensity or by adding a photosynthesis inhibitor. The induced decrease had a greater influence on bacterial respiration than on bacterial production and growth rate, especially at an optimal light intensity. This suggests that changes in primary production drive bacterial activity, but the effect on carbon flow may be mitigated by increased bacterial growth efficiencies, especially of light-dependent AAP bacteria. Bacterial activities were independent of changes in bacterial community composition, which were driven by light availability and AAP bacteria. This direct effect of light on composition of bacterial communities has not been documented previously.

Nitrogen-fixing cyanobacteria as a potential resource for efficient biodiesel production

The incessant utilization of non-renewable energy sources persistently pollutes the earth's atmosphere and thus requires the immediate substitution by renewable energy sources such as biofuel. In this study, several nitrogen-fixing cyanobacteria are screened for biodiesel production on the basis of biomass productivity, lipid productivity, lipid profiling, and harvesting potential. The assessment performed led to the identification of Nostoc sp. MCC41, a nitrogen ficxing cyanobacteria as promising species (0.39 day−1 specific growth rate, biomass productivity of 540 mg L−1 day−1, lipid productivity of 84 mg L−1 day−1 and 15.7% lipid content). A simple filtration experiment shows that almost 81% of the biomass of Nostoc sp. MCC41 is harvested without flocculation aid, while only 23–45% of the green algae (control) could be filtered. Based on the results, further optimization of Nostoc sp. MCC41 is carried out. The optimum light intensity to attain the highest lipid productivity is found to be 54 μmol photon m−2 s−1. Continuous illumination rather than other photoperiods is superior in terms of lipid productivity. Moreover, Nostoc sp. MCC41 could grow under mixotrophic conditions revealing the potential towards an organic carbon-rich wastewater treatment. At 0.5% glucose, the Nostoc sp. MCC41 exhibited nearly five-fold increase in biomass productivity when compared to the phototrophic conditions. Lipid profiling uncovered that Nostoc sp. MCC41 has a high concentration of palmitic acid, indicating its suitability for biodiesel. Given its easy mode of harvesting, ability to grow under mixotrophic condition, and ability to fix atmospheric nitrogen, Nostoc sp. MCC41 can be considered as a potential and eco-friendly resource for efficient biodiesel production.

Optimal light intensity for sustainable water and energy use in indoor cultivation of lettuce and basil under red and blue LEDs

Indoor plant cultivation systems are gaining increasing popularity because of their ability to meet the needs of producing food in unfavourable climatic contexts and in urban environments, allowing high yield, high quality, and great efficiency in the use of resources such as water and nutrients. While light is one of the most important environmental factors affecting plant development and morphology, electricity costs can limit the widespread adoption of indoor plant cultivation systems at a commercial scale. LED lighting technologies for plant cultivation are also rapidly evolving, and lamps for indoor cultivation are often designed to optimize their light emissions in the photosynthetically active spectrum (i.e. red and blue), in order to reduce energetic requirements for satisfactory yield. Under these light regimens, however, little information is available in literature about minimum photosynthetic photon flux density (PPFD) for indoor production of leafy vegetables and herbs, while existing literature often adopts light intensities from 100 to 300 μmol m-2 s-1. This study aims at defining the optimal PPFD for indoor cultivation of basil (Ocimum basilicum L.) and lettuce (Lactuca sativa L.), by linking resource use efficiency to physiological responses and biomass production under different light intensities. Basil and lettuce plants were cultivated at 24 °C and 450 μmol mol-1 CO2 under red and blue light (with red:blue ratio of 3) and a photoperiod of 16 h d-1 of light in growth chambers using five PPFD (100, 150, 200, 250 and 300 μmol m-2 s-1, resulting in daily light integrals, DLI, of 5.8, 8.6, 11.5, 14.4 and 17.3 mol m-2 d-1, respectively). A progressive increase of biomass production for both lettuce and basil up to a PPFD of 250 μmol m-2 s-1 was observed, whereas no further yield increases were associated with higher PPFD (300 μmol m-2 s-1). Despite the highest stomatal conductance associated to a PPFD of 250 μmol m-2 s-1 in lettuce and to a PPFD ≥ 200 μmol m-2 s-1 in basil, water use efficiency was maximized under a PPFD ≥ 200 μmol m-2 s-1 in lettuce and PPFD ≥ 250 μmol m-2 s-1 in basil. Energy and light use efficiencies were increased under a PPFD of 200 and 250 μmol m-2 s-1 in lettuce and under a PPFD of 250 μmol m-2 s-1 in basil. Furthermore, in lettuce grown under 250 μmol m-2 s-1 antioxidant capacity, phenolics and flavonoids were higher as compared with plants supplied with PPFD ≤ 150 μmol m-2 s-1. Accordingly, a PPFD of 250 μmol m-2 s-1 seems suitable for optimizing yield and resource use efficiency in red and blue LED lighting for indoor cultivation of lettuce and basil under the prevailing conditions of the used indoor farming set-up.

Changes in the transcriptome, ploidy, and optimal light intensity of a cryptomonad upon integration into a kleptoplastic dinoflagellate

Endosymbiosis of unicellular eukaryotic algae into previously nonphotosynthetic eukaryotes has established chloroplasts in several eukaryotic lineages. In addition, certain unicellular organisms in several different lineages ingest algae and utilize them as temporal chloroplasts (kleptoplasts) for weeks to months before digesting them. Among these organisms, the dinoflagellate Nusuttodinium aeruginosum ingests the cryptomonad Chroomonas sp. and enlarges the kleptoplast with the aid of the cryptomonad nucleus. To understand how the cryptomonad nucleus is remodeled in the dinoflagellate, here we examined changes in the transcriptome and ploidy of the ingested nucleus. We show that, after ingestion, genes involved in metabolism, translation, and DNA replication are upregulated while those involved in sensory systems and cell motility are downregulated. In the dinoflagellate cell, the cryptomonad nucleus undergoes polyploidization that correlates with an increase in the mRNA levels of upregulated genes. In addition, the ingested nucleus almost loses transcriptional responses to light. Because polyploidization and loss of transcriptional regulation are also known to have occurred during the establishment of endosymbiotic organelles, these changes are probably a common trend in endosymbiotic evolution. Furthermore, we show that the kleptoplast and dinoflagellate are more susceptible to high light than the free-living cryptomonad but that the ingested nucleus reduces this damage.

Optimum interaction of light intensity and CO2 concentration in bioremediating N-rich real wastewater via assimilation into attached microalgal biomass as the feedstock for biodiesel production

Impoverishing nutrients from wastewater via assimilation into microalgal biomass has gained footprint in bioremediation technologies. To ease the harvesting of mature microalgal biomass from effluent, this study proposed the employment of fluidized bed bioreactor to grow attached microalgal biomass onto polyurethane foam support material while bioremediating the N-rich real wastewater from chemical fertilizer manufacturing industry. The complete removals of all nitrogen species (NH4+-N, NO2−-N and NO3−-N) together with COD and total phosphorus were achieved at the optimum light intensity and CO2 concentration of 216μmol/m2 s and 9.1 %, respectively, giving rise to the attached microalgal biomass productivity of 0.094g/L/day. These performances were also found maintaining for at least 4 cycles of reiterative uses of spent polyurethane foam support material in similar fluidized bed bioreactor setup condition with every cycle being introduced with fresh N-rich real wastewater. The mechanism of attachment formations study predicted that the polysaccharides and proteins from microalgal extracellular polymeric substances had bridged the cells onto polyurethane foam support material during the initial colonization prior to populating and growing to cover the surfaces of support material. For biodiesel production, the extracted neutral lipid content of attached microalgal biomass was found to be four times higher than the suspended growth culture. From the transesterification process, about 97 %–98 % of attached microalgal lipid could be converted into fatty acid methyl esters (FAMEs) mixture. Interestingly, the degree of saturated fatty acids (SFA) in FAMEs was recorded increasing with the increase of cycles of reusing spent polyurethane foam support material. The presence of more SFA in FAMEs could overall enhance the oxidative stability and contribute to higher cetane number of produced biodiesel from facilely harvested attached microalgal biomass.

Photoperiod mediates the differential physiological responses of smaller Thalassiosira pseudonana and larger Thalassiosira punctigera to temperature changes

Global warming is altering both phytoplankton-experienced temperature and light-exposure duration through shifting their niches from low to high latitudes. We explored the growth, physiology, and compositions of a smaller Thalassiosira pseudonana and a larger Thalassiosira punctigera, temperate marine centric diatoms, in responses to a matrix of temperatures (12, 15, 18, and 21 °C) and photoperiods (light:dark cycles of 4:20, 8:16, 16:8, and 24:0). Both T. pseudonana and T. punctigera grew faster under medium temperature and longer photoperiod, under the expected optimal instantaneous light intensity. The biovolume-based pigments content of T. pseudonana responded largely to temperature, while that of T. punctigera responded more to photoperiod duration than to temperature. In T. pseudonana, shortest photoperiod enhanced cellular protein content and alleviated their temperature dependency. Continuous growth light reduced the photosynthetic capacity of T. pseudonana at the lowest temperature and reduced that of T. punctigera across temperatures. Moreover, we found the increasing temperature linearly increased the dark respiration rate (Rd) and molar ratio of carbon to nitrogen (C:N) of T. pseudonana but decreased that of T. punctigera, with the scattered effects of photoperiod. Our results demonstrated that responses of diatoms Thalassiosira across photoperiods and temperatures vary with species and possibly with cell size, suggesting that the poleward shift of the niches of phytoplankton in nature might cause a change in community structure.

Lipid and biodiesel production by cultivation isolated strain Chlorella sorokiniana pa.91 and Chlorella vulgaris in dairy wastewater treatment plant effluents.

The present study provided a comparison of two species of microalgae growth in dairy wastewater treatment plant effluents. In optimum conditions their operation to biomass production, lipid accumulation and fatty acids methyl ester composition so as to biodiesel production is studied. For the first time, the not sterilized effluents of dairy wastewater treatment plant was used as the culture mediums of native microalgae, Chlorella sorokiniana strain pa.91, and another one Chlorella vulgaris. They were cultured under 5 light intensity levels so as to find optimum conditions to observed high biomass and lipid production. At the optimum light intensity the composition of fatty acids methyl ester in their lipids was analyzed by GC-MS. The light intensity of 7500 Lux was obtained as the optimum for both microalgae to produce high biomass. The biomass productivity of C. sorokiniana pa.91 and C. vulgaris in preliminary treated effluent at this light intensity was obtained 0.233 and 0.214gL-1day-1, respectively. This parameter in secondary treated effluent was achieved 0.185 and 0.166gL-1day-1, respectively. Moreover, the highest lipid content of their biomass was observed at the light intensity of 2500 Lux. At this light intensity and at the preliminary effluent the maximum lipid content of C. sorokiniana pa.91 and C. vulgaris was observed 31% and 34%, respectively and at the secondary one it was obtained 35% and 36.67%, respectively. Based on the results, the fatty acids composition in the lipids of microalgae C. sorokiniana pa.91 and C. vulgaris cultured in both effluents had the high amount of cetane number which is really useful for high quality biodiesel production. Also, the other valuable properties which produce the high quality biodiesel were the obtained amounts of CFPP and CP which shown a high performance potential biodiesel even at low temperatures. This feature was obtained, on the grounds that the unsaturated fatty acid was obtained more than saturated fatty acid. The nutrients-rich media of dairy wastewater effluents were applicable to growth both microalgae and useful biomass production, lipid accumulation and fatty acids profiling. Furthermore, the compounds of fatty acids had the best conditions to biodiesel production especially in cold weather areas.

Low temperature and high light dependent dynamic photoprotective strategies in Arabidopsis thaliana.

Arabidopsis thaliana has been recognized as a chilling tolerant species based on analysis of resistance to low temperature stress, however, the mechanisms involved in this tolerance are not yet clarified. The low temperature-induced effects are exacerbated when plants are exposed to low temperatures in the presence of high light irradiance but the experimental data on the impact of light intensity during cold stress and its influence during recovery from stress are rather limited. The main objective of this study was to re-examine the photosynthetic responses of A. thaliana plants to short term (6 days) low temperature stress (12/10°C) under optimal (150 μmol m-2 s-1 ) and high light (500 μmol m-2 s-1 ) intensity and the subsequent recovery from the stress. Simultaneous measurements of the in vivo and in vitro functional performance of both photosystem II (PSII) and photosystem I (PSI), as well as, net photosynthesis, low temperature (77 K) chlorophyll fluorescence and immunoblot analysis of the relative abundance of PSII and PSI reaction center proteins were used to evaluate the role of light in the development of possible protective mechanisms during low temperature stress and the consequent recovery from exposure to low temperature and different light intensities. The results presented clearly suggest that Arabidopsis plants can employ a number of highly dynamic photoprotective strategies depending on the light intensity. These strategies include one based on LHCII quenching and two other quenching mechanisms localized within the PSII and PSI reaction centers, which are all expressed to different extent depending on the severity of the photoinhibitory treatments under low temperature stress conditions.

Improved lipid productivity of Chlamydomonas globosa and Oscillatoria pseudogeminata as a biodiesel feedstock in artificial media and wastewater

Chlamydomonas globosa and Oscillatoria pseudogeminata were grown under different growth conditions on artificial and agricultural wastewater as growth media for biodiesel production. C. globosa and O. pseudogeminata were able to grow in a range of temperatures from 15 to 37 °C and the maximum percentage of total lipid productivity/dry weight was attained after one week of incubation. The optimal pH and light intensity for the growth and lipid productivity were 8.5 and 1000 lux, respectively. The non-irradiated microalgae showed higher growth and lipid content than the irradiated ones with gamma radiation at different doses. The optimal growth and lipid productivity for the algal strains were reached at N/P ratio: 45 using 0.05 and 0.00174 gl-1 for nitrogen and phosphorus concentrations, respectively. The percentages of the produced lipid in sterilized agricultural wastewater compared to the lipids produced in the modified BG-11 were 69% for C. globosa and 76% for O. pseudogeminata. The most common fatty acids of the two algal strains were palmetic acid, stearic acid, oleic acid, linoleic acid and linolenic acid. According to the obtained results in this study, C. globosa and O. pseudogeminata were found to be highly efficient in producing total lipids for biodiesel and can be used in artificial media and wastewaters as growth media for biodiesel production.

Different Microgreen Genotypes Have Unique Growth and Yield Responses to Intensity of Supplemental PAR from Light-emitting Diodes during Winter Greenhouse Production in Southern Ontario, Canada

Low natural daily light integrals (DLIs) are a major limiting factor for greenhouse production during darker months (e.g., October to February in Canada). Supplemental lighting (SL) is commonly used to maintain crop productivity and quality during these periods, particularly when the supply chain demands consistent production levels year-round. What remains to be determined are the optimum SL light intensities (LIs) for winter production of a myriad of different commodities. The present study investigated the growth and yield of sunflower (Helianthus annuus L., ‘Black oil’), kale (Brassica napus L., ‘Red Russian’), arugula (Eruca sativa L.), and mustard (Brassica juncea L., ‘Ruby Streaks’), grown as microgreens, in a greenhouse under SL light-emitting diode (LED) photosynthetic photon flux density (PPFD) levels ranging from 17.0 to 304 μmol·m−2·s−1 with a 16-hour photoperiod (i.e., supplemental DLIs from 1.0 to 17.5 mol·m−2·d−1). Crops were sown in a commercial greenhouse near Hamilton, ON, Canada (lat. 43°14′N, long. 80°07′W) on 1 Feb. 2018, and harvested after 8, 11, 12, and 12 days, resulting in average natural DLIs of 6.5, 5.9, 6.2, and 6.2 mol·m−2·d−1 for sunflower, kale, arugula, and mustard, respectively. Corresponding total light integrals (TLIs) ranged from 60 to 188 mol·m−2 for sunflower, 76 to 258 mol·m−2 for kale, 86 to 280 mol·m−2 for arugula, and 86 to 284 mol·m−2 for mustard. Fresh weight (i.e., marketable yield) increased asymptotically with increasing LI and leaf area increased linearly with increasing LI, in all genotypes. Hypocotyl length of mustard decreased and hypocotyl diameter of sunflower, arugula, and mustard increased with increasing LI. Dry weight, robust index, and relative chlorophyll content increased and specific leaf area decreased in kale, arugula, and mustard with increasing LI. Commercial microgreen greenhouse growers can use the light response models described herein to predict relevant production metrics according to the available (natural and supplemental) light levels to select the most appropriate SL LI to achieve the desired production goals as economically as possible.

Enhancing growth and phytochemicals of two amaranth microgreens by LEDs light irradiation

The effects of light factors affecting growth and quality of vegetables and fruits at mature stages have been often reported while for that of microgreens is still limited. This study was to determine the optimum light spectrum, light intensity and photoperiod that enhanced growth and nutritional values of amaranth microgreens by using light-emitting diodes (LEDs). Two amaranth cultivars, red amaranth and leafy vegetable amaranth, were cultured for 8 days under different light spectra, light intensities and photoperiods provided by LEDs. Three consecutive experiments in the split-plot design were conducted by which, for each experiment, light treatment was a main-plot factor and amaranth cultivar was a sub-plot factor. The first experiment, amaranth microgreens were irradiated by different light spectra: red, blue, red plus blue (70R:30B) and white with photosynthetic photon flux density (PPFD) of 130 μmol m−2 s-1. The second experiment, the plants were illuminated under various light intensities: 130, 180, 230, 280 μmol m−2 s-1 PPFD with red plus blue (70R:30B) spectrum. The third experiment, the microgreens were treated with different photoperiods: 8, 12, 16, 20 h (h) under red plus blue (70R:30B) spectrum and 280 μmol m−2 s-1 PPFD. The results indicated that red plus blue (70R:30B) spectrum, 280 μmol m−2 s-1 PPFD and 16 h photoperiod enhanced the fresh yield, chlorophyll a, b, total carotenoids, anthocyanin, and vitamin C contents and total antioxidant capacity for both red amaranth and leafy vegetable amaranth microgreens. The cultivar differences in the responses to light spectra and photoperiods were found.

Vegetable and food crop production with micro climate modification

Vegetable and food crops generally require optimum light intensity so that most of these plants are cultivated monoculture. This research has tried to produce food and vegetable crops in the planting system with a perennial crop. This might be a solution to land limitations, and opportunity modification for the cultivation of food crops and vegetables in sites that tend to be shaded and less light intensity. This research was carried out in Nokilalaki Subdistrict which is directly bordered with the conservation area, i.e. Lore Lindu National Park. The study was designed in factorial design method of randomized block design, that consists of two factors, such as food crop species (tomatoes, chillies, sweet potatoes, taro) and pruning degrees of perennial crops (low pruning/25% of light intensity, moderate pruning/50% of light intensity, and heavy pruning/75% of light intensity. The results showed that the highest crop production was provided on sweet potatoes yield of 18.5 tons ha−1 at 50% of light intensity, but was not significant different in 75% of light intensity (17.1 tons ha−1). Tomato and taro yield was not significantly different between all light intensity. So tomatoes and taro might be introduced into a variety of microclimate conditions.

Флуоресцентные характеристики диатомовой водоросли Cylindrotheca closterium (Ehrenberg) Reimann et Lewin, 1964

Исследованы флуоресцентные характеристики диатомовой водоросли Cylindrotheca closterium, предварительно выращиваемой при интенсивности света 17, 200 и 800 мкЭ·м−2·с−1. Показана возможность применения флуоресцентных параметров для экспресс-оценки общего функционального состояния водорослей и для выявления диапазона оптимальных для их роста освещённостей. Параметр Fv/Fm позволяет в экспресс-режиме оценивать функциональное состояние водорослей в условиях их интенсивного культивирования. Показано, что максимальный коэффициент переменной флуоресценции (Fv/Fm) составлял 0,65–0,7 для водорослей, растущих при освещённости 17 и 200 мкЭ·м−2·с−1, и снижался до 0,48–0,57 для водорослей, адаптированных к интенсивности света 800 мкЭ·м−2·с−1. Получены световые зависимости скорости электронного транспорта и фотохимического и нефотохимического тушения флуоресценции хлорофилла, а также значения коэффициента Fv’/Fm’. Эти параметры показывают степень устойчивости водорослей к уровню светового фактора. Показано, что оптимальной для роста C. closterium является насыщающая освещённость около 200 мкЭ·м−2·с−1. Высокие значения флуоресценции на единицу хлорофилла при экстремальной освещённости (800 мкЭ·м−2·с−1) могут указывать на степень инактивации части реакционных центров фотосистемы II.

Photovoltaic Properties of an rGO/Pt Counter Electrode With AZO Photoanode for Dye-Sensitized Solar Cells Under Low Light Intensity

This study used reduced graphene oxide (rGO) applied to a platinum (Pt) counter electrode to improve light conversion efficiency. The study also used an Al-doped Zinc Oxide (AZO) nanosheet/TiO2 photoanode for the dye-sensitized solar cell (DSSC). Photovoltaic characteristics, electrochemical impedance spectroscopy (EIS), field-emission scanning electron microscopy (FE-SEM) and Raman spectroscopy were used to analyze DSSC. The different light intensities and photovoltaic characteristics were analyzed to determine optimal light intensity conditions. The unmodified Pt counter electrode was compared with the rGO/Pt counter electrode, photovoltaic conversion efficiency ( ${\eta }$ ) increased from 3.60% to 4.04% due to the rGO modification as it possesses a higher specific surface area. Its low cost also makes it suitable for mass production. In addition, an AZO nanosheet/TiO2 photoanode was fabricated to form a double-layer structure in which photovoltaic conversion efficiency was 4.47 %. Finally, a DSSC with an AZO/TiO2 photoanode and rGO/Pt counter electrode was fabricated and had an photovoltaic conversion efficiency of 5.05 %. This study also analyzed the photovoltaic parameters of DSSC under different light intensities, which shows the optimal photovoltaic conversion efficiency of 5.54% under 30mW/cm2.

Evaluation of the interaction of temperature and light intensity on the growth of Phaeodactylum tricornutum: Kinetic modeling and optimization

In this study, the effects of two highly variable factors, temperature ranging from 10–35 °C and light intensity from 98–1289 μmol m−2s-1, on the specific growth rate, μ, of a diatom, Phaeodactylum tricornutum, at a constant aeration rate of 3000 cm3 min-1 were elucidated. The choice of the adequate kinetic models describing the growth related to temperature and light intensity resulted in rapid determination of optimum growth conditions. Ratkowsky’s square root model and Monod-type model were assessed as the most suitable expressions among the three temperature- and eight light intensity-dependent models, respectively, presenting the highest adjusted R2 and smallest average relative deviation (ARD) values by means of nonlinear least squares method. Also, among the kinetic model approaches utilized to verify the combined effects of temperature and light intensity, the temperature-dependent Ratkowsky model in conjunction with the Monod-type expression with the smallest ARD value (4.19 %) and a high adjusted R2 (0.9775) exhibited the best surface fit. The optimum cultivation temperature and light intensity conditions for the achieving maximum specific growth rate of P. tricornutum were determined as 21 °C and 496 μmol m−2s-1, respectively, by the help of the Central Composite Design (CCD) of the Response Surface Methodology (RSM).

Reducing Energy Requirements in Future Bioregenerative Life Support Systems (BLSSs): Performance and Bioactive Composition of Diverse Lettuce Genotypes Grown Under Optimal and Suboptimal Light Conditions.

Space farming for fresh food production is essential for sustaining long-duration space missions and supporting human life in space colonies. However, several obstacles need to be overcome including abnormal light conditions and energy limitations in maintaining Bioregenerative Life Support Systems (BLSSs). The aim of the present study was to evaluate six lettuce cultivars (baby Romaine, green Salanova, Lollo verde, Lollo rossa, red oak leaf and red Salanova) of different types and pigmentations under optimal and suboptimal light intensity and to identify the most promising candidates for BLSSs. Baby Romaine performed better than the rest of the tested cultivars under suboptimal light intensity, demonstrating a more efficient light-harvesting mechanism. Stomatal resistance increased under suboptimal light conditions, especially in the case of Lollo verde and red oak leaf cultivars, indicating stress conditions, whereas intrinsic water-use efficiency was the highest in baby Romaine and red oak leaf cultivars regardless of light regime. Nitrate content increased under suboptimal light intensity, especially in the cultivars green Salanova and Lollo verde, while P and Ca accumulation trends were also observed in baby Romaine and Lollo verde cultivars, respectively. Chicoric acid was the major detected phenolic acid in the hydroxycinnamic derivatives sub-class, followed by chlorogenic, caffeoyl-tartaric and caffeoyl-meso-tartaric acids. Chicoric and total hydroxycinnamic acids were not affected by light intensity, whereas the rest of the detected phenolic compounds showed a varied response to light intensity. Regarding cultivar response, red oak leaf exhibited the highest content in chicoric acid and total hydroxycinnamic acids content under suboptimal light intensity, whereas red Salanova exhibited the highest hydroxycinnamic derivatives profile under optimal light conditions. The main detected carotenoids were β-cryptoxanthin and violaxanthin+neoxanthin, followed by lutein and β-carotene. All the target carotenoids decreased significantly under low light intensity, while red Salanova maintained a distinct carotenoids profile. Overall, cultivation of assorted lettuce cultivars is the optimal scenario for space farming, where baby Romaine could provide adequate amounts of fresh biomass owing to its high light-use efficiency while red oak leaf and red Salanova could contribute to the daily dietary requirements for health-promoting bioactive compounds such as polyphenols and carotenoids.

High density orcharding and canopy management of some tropical and subtropical fruits

High density planting (HDP) is a highly efficient and advanced production system of fruit cultivation. In most of the temperate tree and nut crops it is now commercially followed all over the world because of availability of suitable dwarfing rootstock to control tree vigor. Major tropical fruit crops are either propagated by suckers (banana, pineapple), seed (papaya) or by layering (guava) and grafting (mango). The use of dwarfing rootstocks, as in many temperate tree fruits, is not possible/available in most of the commercial tropical fruits for high density planting. High density planting is one of the novel methods to achieve high productivity per unit area both in short duration and perennial horticultural crops. High yield and high fruit quality can be achieved with a high-density orchard when the orchard has good light distribution throughout the tree canopy and there is a balance between vegetative growth and cropping. Many variables must be included in making a decision about spacing. Tree vigor and growth habit as influenced by cultivar and rootstock (where it could be utilized) are important. The ultimate limit on productivity of any crop is the amount of photosynthetically-active radiation (PAR) intercepted. Much of the planning that goes into the design of HDP orchards is actually based on average light interception over the life of the planting. This involves both minimizing the amount of light which strikes the ground and providing canopy structures in which the largest amount of canopy receives optimum light intensity. A tree with a large portion of its volume devoted to bearing has a greater potential for productivity than one with most of its volume devoted to tree support, middles or other functions. In India, HDP has been proved useful in many tropical and subtropical fruit crops e.g., mango, citrus, pineapple, banana, guava litchi, and papaya. The productivity of fruit crops depends on several factors, poor management of canopy architecture being the most important one. The fruiting potential of the trees is largely governed by their architecture, canopy density and photosynthetic efficiency. Canopy in a fruit tree refers to its physical composition comprising of the stem, branches, shoots and leaves. While, the canopy density is determined by the number, length and orientation of stem, branches and shoots. Tree canopy management, especially size control has become a priority for reducing production cost and increasing fruit yield and quality. The objective of canopy management is to optimize the plant model in such a way so that it may intercept maximum light by tree training, pruning, branch and tree orientation. Some of the basic principles in canopy management are: maximum utilization of the light, avoidance of the buildup of micro-climate congenial for the diseases and pests, convenience in carrying out the cultural operations, maximizing the productivity and quality and economy in obtaining the required canopy architecture.

DESIGN AND EVALUATION OF A HELICAL-TUBULAR PHOTOBIOREACTOR FOR MICROALGAE PRODUCTION

Photosynthetic microalgae are important bioresource for producing desired and environmentally safe products including biodiesel production as third generation biofuels. Photobioreactor play important role in this process. Designing and manufacture the bioreactor for photocatalysis is still challenging at present time due to the important factors that must be closely considered with regard to light requirements. The aim of the present study was to design and evaluate a helical-tubular photobioreactor for algae production. The design considerations included light intensity controller circuit, surface-to-volume ratio, power required of both air pump and mixing pump to reach up the optimum operating parameters. Experiments were conducted to optimize light intensity and light/dark duration cycle. The photobioreactor performance was evaluated in terms of biomass productivity, lipid productivity, carbon capture efficiency and energy balance of algae production system. The experimental results reveal that the helical-tubular photobioreactor is recommended to be used under light intensity of 8 kLux and light/dark duration cycle of 18:6 h to obtain the highest biomass productivity of 1.80 kg.day-1 and lipid productivity 432 g.day-1 with carbon capture efficiency 87%. The manufactured photobioreactor is capable of produce 4.74 kWday which is equivalent to 4.39 kWday of net energy output.