Optimal Light Level Research Articles

Adaptation of indoor ornamental plants to various lighting levels in growth chambers simulating workplace environments

Despite the growing interest in indoor greenery and its positive effects on occupants’ well-being, there is limited knowledge on the optimal light levels for indoor plants that ensure energy efficiency and sustainable growth. This study explored the survival of ornamental plants under low-light conditions typical of indoor workplaces without daylight and investigated the impact of increased light intensity or extended day length on their growth. Three species of foliage plants (Epipremnum aureum, Pachira aquatica, and Rhaphidophora tetrasperma) were cultivated in growth chambers with three different lighting schemes. The results showed that plants sustained growth with 6.8 μmol m−2 s−1 white LED light for 9 h/day, suggesting that extra lighting might not be necessary for shade-tolerant species in offices. In this environment, plants maintained efficient photosynthesis under low illumination by increasing their specific leaf area. Elevating the light to 20.1 μmol m−2 s−1 and extending the day length to 18 h/day enhanced the plants’ relative growth rate. Climbing plants allocated more biomass to stems, resulting in a lower leaf weight ratio and noticeably altering their appearance. This study demonstrates that customized lighting strategies effectively support indoor greening goals, like adjusting intensity for energy savings or adding light for greening large spaces.

Rethinking Zero-DCE for Low-Light Image Enhancement

Zero-Reference Deep Curve Estimation (Zero-DCE) is currently one of the most popular low-light image enhancement methods. Through extensive experimentation, we observe that: (i) the excellent performance of Zero-DCE depends on the training data with multiple exposure levels, (ii) it cannot effectively handle uneven light, extremely low light, or overexposed images in natural environments. Therefore, we propose an improved zero-reference dual-illumination deep curve estimation method for low-light image enhancement named Zero-DiDCE, which can enhance, suppress, or maintain light levels for images. The adaptive light enhancement curve was designed to handle images with different exposure levels. An iterator and amplitude controller are designed to control the curve enhancement intensity by calculating the gap between the input image and the optimal light level. Furthermore, instead of the DCE-Net in Zero-DCE only taking the input image as network input, our DiDCE-Net in Zero-DiDCE takes the input image and the inverted input image simultaneously as network input to ensure that the training set contains samples with multiple exposure levels. A piecewise non-reference loss function is designed to guide the training of DiDCE-Net from the perspective of information loss. Qualitative and quantitative experiments show that our method can handle images with different levels of exposure well and outperforms state-of-the-art methods. In addition, the proposed curve and iterator can be integrated into other methods to improve their enhancement effects. The code is available at https://github.com/Wenhui-Luo/Zero-DiDCE.

Dominance of photo over chromatic acclimation strategies by habitat-forming mesophotic red algae.

Red coralline algae are the deepest living macroalgae, capable of creating spatially complex reefs from the intertidal to 100+ m depth with global ecological and biogeochemical significance. How these algae maintain photosynthetic function under increasingly limiting light intensity and spectral availability is key to explaining their large depth distribution. Here, we investigated the photo- and chromatic acclimation and morphological change of free-living red coralline algae towards mesophotic depths in the Fernando do Noronha archipelago, Brazil. From 13 to 86 m depth, thalli tended to become smaller and less complex. We observed a dominance of the photo-acclimatory response, characterized by an increase in photosynthetic efficiency and a decrease in maximum electron transport rate. Chromatic acclimation was generally stable across the euphotic-mesophotic transition with no clear depth trend. Taxonomic comparisons suggest these photosynthetic strategies are conserved to at least the Order level. Light saturation necessitated the use of photoprotection to 65 m depth, while optimal light levels were met at 86 m. Changes to the light environment (e.g. reduced water clarity) due to human activities therefore places these mesophotic algae at risk of light limitation, necessitating the importance of maintaining good water quality for the conservation and protection of mesophotic habitats.

Nursery optimization for kelp aquaculture in the Southern Hemisphere: the interactive effects of temperature and light on growth and contaminants

ABSTRACT Kelp aquaculture is typically a two-stage process, with an indoor nursery phase and a grow-out phase at sea. For the successful development and implementation of commercial kelp aquaculture, production of viable seeded lines in the nursery is essential. This study investigated optimal nursery conditions of three kelp species native to Tasmania, Australia: Ecklonia radiata, Lessonia corrugata, and Macrocystis pyrifera. The interactive effects of temperature (12°C, 15°C, and 18°C) and light level (~30 µmol photons s−1 m−2, and ~ 60 µmol photons s−1 m−2) on sporophyte length, sporophyte density, and contamination of spools were examined over a 34-day period. The optimal temperature and light levels were 15°C and 30 µmol photons m−2 s−1 for E. radiata, 12°C and 60 µmol photons m−2 s−1 for L. corrugata, and 12°C and 30 or 60 µmol photons m−2 s−1 for M. pyrifera. Under these optimal conditions, the mean ± SEM sporophyte lengths after 34 days were 0.60 ± 0.02 mm, 1.04 ± 0.04 mm, and 0.60 ± 0.01 mm for E. radiata, L. corrugata, and M. pyrifera, respectively. The mean ± SEM sporophyte densities for each of these three species were 15.5 ± 6.2 sporophytes cm−1 of line, 10.8 ± 5.9 sporophytes cm−1 of line, and 19.3 ± 8.1 sporophytes cm−1 of line, respectively. Contamination increased with increasing temperature and was not significantly affected by light level. This work highlights the need for a species- and ecotype-specific approach in the nursery phase to ensure successful seaweed aquaculture outcomes in new regions of cultivation.

Factors influencing the state of blinds and lights in primary schools: Behavioural models and opportunities to improve children's visual environment

The state of blinds and lights affects children's visual environment and comfort, however, there is a significant gap in research on the factors leading to the operation of blinds and lights in primary school classrooms. This study identifies and categorises the main drivers of operations on blinds and lights and investigates optimal light levels for children in primary schools. The study collected measurements of environmental variables, observations of operations on blinds and lights using forms and time-lapse cameras and visual sensation questionnaires in 31 naturally ventilated classrooms in the UK for one year. Results suggest that operations on blinds and lights are influenced by a range of contextual, occupant-related and building-related factors. Behavioural models of blind and light operation in primary schools are developed using the data collected. With regards to children's visual comfort, in the current study, at 730 lux, 80% of the children were satisfied with the light level in their classroom. The findings and models presented in this study could be used by designers of schools to achieve more visually comfortable classrooms. For example, the results suggest that vertical blinds rather than roller blinds may be a better design choice for classrooms as their slats can be adjusted to control direct sunlight but also allow ventilation. The research concludes with a range of strategies for managing the visual environment through operations on blinds to both reduce lighting energy consumption, as well as increase the quality of the visual environment thereby improving school children's health and productivity.

Perbedaan konsentrasi nitrat dan intensitas cahaya terhadap laju pertumbuhan diatom Chaetoceros muelleri

Microalgae are cultured as natural feed for the cultivation of mollusks, crustaceans (early larval stages), and zooplankton. Diatoms are phytoplankton groups commonly used as feed, one of which is Chaetoceros muelleri. This study aims to identify the optimal nitrate concentrations and light level (irradiance) for the growth rate of C. muelleri. Culture was placed in nitrate 1,330; 5,305; and 27,030 mg/L (N1, N2, N3, respectively); and light 50, 100, and 150 µmol/m2/s, with three replications for each treatment. The response variable observed was the growth rate of C. muelleri and nitrate uptake. Each nitrate treatment resulted in a significant difference in the growth rate of C. muelleri (LSD, p < 0.01). The N3 treatment produced the highest growth rate (average 0,188-0,193 cells/day), while N1 produced the lowest specific growth rate (average 0,149-0,157 /day). In light treatment, a significant difference was only seen in the light level of 150 µmol/m2/s (LSD, p < 0.05) which produced the highest growth rate (average 0.157-0.193 cells/day), especially in the nitrate N1 and N2. Meanwhile based on the significance test, the interaction between nitrate and light treatment was not significant.Keywords: Chaetoceros muelleri; Growth rate; Irradiance; Nitrate

Variation of nitrate concentration and light level on growth rate of diatom Chaetoceros muelleri

Microalgae are cultured as natural feed for the cultivation of mollusks, crustaceans (early larval stages), and zooplankton. Diatoms are phytoplankton groups commonly used as feed, one of which is Chaetoceros muelleri. This study aims to identify the optimal nitrate concentrations and light level (irradiance) for the growth rate of C. muelleri. Culture was placed in nitrate 1,330; 5,305; and 27,030 mg/L (N1, N2, N3, respectively); and light 50, 100, and 150 µmol/m2/s, with three replications for each treatment. The response variable observed was the growth rate of C. muelleri and nitrate uptake. Each nitrate treatment resulted in a significant difference in the growth rate of C. muelleri (LSD, p < 0.01). The N3 treatment produced the highest growth rate (average 0,188-0,193 cells/day), while N1 produced the lowest specific growth rate (average 0,149-0,157 /day). In light treatment, a significant difference was only seen in the light levelof 150 µmol/m2/s (LSD, p < 0.05) which produced the highest growth rate (average 0.157-0.193 cells/day), especially in the nitrate N1 and N2. Meanwhile based on the significance test, the interaction between nitrate and light treatment was not significant.Keywords: Chaetoceros muelleri; Growth rate; Irradiance; Nitrate

Comparative Analysis of Machine Learning and Evolutionary Optimization Algorithms for Precision Micropropagation of Cannabis sativa: Prediction and Validation of in vitro Shoot Growth and Development Based on the Optimization of Light and Carbohydrate Sources.

Micropropagation techniques offer opportunity to proliferate, maintain, and study dynamic plant responses in highly controlled environments without confounding external influences, forming the basis for many biotechnological applications. With medicinal and recreational interests for Cannabis sativa L. growing, research related to the optimization of in vitro practices is needed to improve current methods while boosting our understanding of the underlying physiological processes. Unfortunately, due to the exorbitantly large array of factors influencing tissue culture, existing approaches to optimize in vitro methods are tedious and time-consuming. Therefore, there is great potential to use new computational methodologies for analyzing data to develop improved protocols more efficiently. Here, we first tested the effects of light qualities using assorted combinations of Red, Blue, Far Red, and White spanning 0–100 μmol/m2/s in combination with sucrose concentrations ranging from 1 to 6% (w/v), totaling 66 treatments, on in vitro shoot growth, root development, number of nodes, shoot emergence, and canopy surface area. Collected data were then assessed using multilayer perceptron (MLP), generalized regression neural network (GRNN), and adaptive neuro-fuzzy inference system (ANFIS) to model and predict in vitro Cannabis growth and development. Based on the results, GRNN had better performance than MLP or ANFIS and was consequently selected to link different optimization algorithms [genetic algorithm (GA), biogeography-based optimization (BBO), interior search algorithm (ISA), and symbiotic organisms search (SOS)] for prediction of optimal light levels (quality/intensity) and sucrose concentration for various applications. Predictions of in vitro conditions to refine growth responses were subsequently tested in a validation experiment and data showed no significant differences between predicted optimized values and observed data. Thus, this study demonstrates the potential of machine learning and optimization algorithms to predict the most favorable light combinations and sucrose levels to elicit specific developmental responses. Based on these, recommendations of light and carbohydrate levels to promote specific developmental outcomes for in vitro Cannabis are suggested. Ultimately, this work showcases the importance of light quality and carbohydrate supply in directing plant development as well as the power of machine learning approaches to investigate complex interactions in plant tissue culture.

Light quality and intensity of light-emitting diodes during pre-cultivation of Picea abies (L.) Karst. and Pinus sylvestris L. seedlings – impact on growth performance, seedling quality and energy consumption

ABSTRACTThree different LED lamps with continuous spectra were compared against commonly used fluorescent lights. The lamps were characterized by light output, energy consumption and spectral quality for plant growth. The biological effects of light quality were compared by pre-cultivating seedlings of Picea abies (L.) Karst. and Pinus sylvestris L. under each spectrum for 35 days in a growth chamber with controlled temperature, humidity and photoperiod. The seedlings were then transplanted and cultivated for one vegetation period at the nursery, then planted outdoors on a forest field trial and followed for three years. The seedlings showed similar growth performance for all spectra tested. LED lamps have several advantages to fluorescent light such as energy consumption, longer life span and adjustable light intensity. Regarding light intensity the effects on growth performance were studied for both species using the most promising LED spectra. The photosynthetically active radiation (PAR) was maintained at 50, 100, 200 and 400 μmol m−2 s−1. Unlike energy consumption, seedling development did not display a linear relationship to light intensity. Instead, the results show an optimum light level between 100 and 200 μmol m−2 s−1 for the shade tolerant Picea abies seedlings and a level of around 200 μmol m−2 s−1 for the more shade intolerant Pinus sylvestris seedlings.

The effect of CO2 in enhancing photosynthetic cofactor recycling for alcohol dehydrogenase mediated chiral synthesis in cyanobacteria

The light harvesting photosystem in cyanobacteria offers a potential pathway for the regeneration of the nicotinamide cofactor NADPH, thereby facilitating the application of cyanobacteria as excellent whole cell biocatalysts in oxidoreductase-mediated biotransformation. The use of cyanobacterial metabolism for cofactor recycling improves the atom economy of the process compared to the commonly employed enzyme-coupled cofactor recycling using enzymes such as glucose dehydrogenase. Here we report the asymmetric conversion of acetophenone to chiral 1-phenylethanol by recombinant Synechococcus elongatus PCC 7942 whole cell biocatalyst that expresses the NADPH dependent L. kefir alcohol dehydrogenase. Besides light, it was observed that carbon dioxide levels play a critical role in improving the bioconversion efficiency possibly due to the enhanced growth rate and improved cofactor availability at elevated CO2 levels. Complete reduction of acetophenone to optically pure (R)-1-phenylethanol at 99% enantiomeric excess was achieved within 6 h with a relatively low cell density of 0.66 g/l by coupling optimum light and CO2 levels and without the need for a co-substrate.

Perceived adequacy of illumination and pedestrians’ night-time experiences in urban obscured spaces: A case of London

This paper discusses lighting for pedestrian in urban obscured spaces and how perceived adequacy of illumination (PAI) might enhance pedestrians’ night-time experiences. A conventional approach is to evaluate human responses under road lighting of different illuminance, but this alone does not enable an optimum light level to be identified. In this study, a total of 30 participants (19 females and 11 males) visited 10 different urban obscured spaces underneath bridges in London. Their night-time experiences such as feelings, suitability of a space, discomfort glare and facial recognition were compared with horizontal illuminance levels and percentages of PAI. The result indicates that horizontal illuminance was associated with perceived quality of facial recognition, perceived ratings of pleasantness and liveliness. However, higher lighting does not seem to result in higher qualities of other night-time experiences in uncontrolled environments. Spaces with higher percentage of PAI are more strongly associated with an increase in pedestrians’ perceptions of pleasantness, liveliness, suitability of spaces and ratings of facial recognition. Perceived level of discomfort glare was found not to be related with neither illuminance level nor PAI percentages. The paper suggests that PAI can be a moderate indicator of an overall night-time experience for pedestrians in obscured spaces.

Sensory exposure of neonates in single-room environments (SENSE): an observational study of light

ObjectivesTo measure the internal and external light exposure of incubators and open cots in an Australian single-room configured neonatal unit and compare findings to current recommendations.MethodsLight meters were placed in...

Variation in sensitivity of large benthic Foraminifera to the combined effects of ocean warming and local impacts

Large benthic foraminifera (LBF) are crucial marine calcifiers in coral reefs, and sensitive to environmental changes. Yet, many species successfully colonise a wide range of habitats including highly fluctuating environments. We tested the combined effects of ocean warming, local impacts and different light levels on populations of the common LBF Amphistegina lobifera collected along a cross-shelf gradient of temperature and nutrients fluctuations. We analysed survivorship, bleaching frequency, chlorophyll a content and fecundity. Elevated temperature and nitrate significantly reduced survivorship and fecundity of A. lobifera across populations studied. This pattern was exacerbated when combined with below optimum light levels. Inshore populations showed a consistent resistance to increased temperature and nitrate levels, but all populations studied were significantly affected by light reduction. These findings demonstrated the capacity of some populations of LBF to acclimate to local conditions; nonetheless improvements in local water quality can ultimately ameliorate effects of climate change in local LBF populations.

Effects of Light Intensity on the Growth, Photosynthetic Characteristics, and Flavonoid Content of Epimedium pseudowushanense B.L.Guo.

Epimedium pseudowushanense B.L.Guo is used in traditional medicine as an aphrodisiac and to strengthen muscles and bones. Several recent reports have shown that flavonoids from Epimedium also significantly affect the treatment of breast cancer, liver cancer, and leukemia. However, few studies have examined the medicinal-ingredient yield of Epimedium, a light-demanding shade herb, under different light intensities. To investigate the effects of light intensity on medicinal-ingredient yields, Epimedium was exposed to five levels of light intensity until harvest time. Leaf dry biomass under L4 was the highest among different light treatments. L4 was also associated with the highest net photosynthetic rate. Quantification of epimedin A, epimedin B, epimedin C, and icariin showed that L3 produced the highest amount of epimedin C, and that flavonoid content responded to light levels differently. Results indicated that L3 and L4 were the optimal light levels for medicinal-ingredient yield.

Optimal light for greenhouse culture of American ginseng seedlings

Three greenhouse experiments with American ginseng seedlings growing under light levels from 4.8% to 68% showed a quadratic response for root dry weight, giving an optimal root dry weight of 239 mg (range 160–415 mg) at an optimal light level of 35.6% (range 30.6–43.2%).

Vertical spatio-temporal patterns of phytoplankton due to migration behaviors in two shallow, microtidal estuaries: Influence on phytoplankton function and structure

Vertical patterns of phytoplankton biomass driven by phytoflagellate migration constitute a natural, short-term process with potentially important impacts on estuarine primary production and community composition. Although often considered well-mixed, phytoflagellate vertical migration patterns have been observed in shallow estuaries. We investigated vertical migration patterns in two shallow estuaries to determine how often and under what environmental conditions vertical migration patterns occurred, and to understand the potential impacts of vertical migration on phytoplankton composition and productivity. Vertical migration patterns were determined from circumannual records of decimeter-scale, semihourly, vertical profiles of chlorophyll fluorescence in two shallow, microtidal estuaries, the New River Estuary and Neuse River Estuary, North Carolina, USA. Observed migration patterns were compared with coincident measures of temperature, salinity, light, turbidity, nutrients, vertical stratification, and wind speed. A simple light × biomass model was used to estimate the influence of vertical migration patterns on total water column primary production. Collectively, between two sites in each estuary, diel vertical migration (DVM) patterns were detected on about half of the days. A secondary migration pattern reflecting a midday descent was also observed and was attributed to avoidance of intense midday surface irradiance. The likelihood of detectable DVM patterns increased under warmer conditions and lower incident irradiance, and at two of the stations was lessened by elevated wind speeds or reduced stratification intensity. Even weak stratification may be sufficient to reduce vertical mixing to levels that allow effective depth regulation by directed swimming. Modeled depth-integrated primary production was increased modestly (<10%) by observed migration patterns compared to a hypothetical vertically-homogenous biomass distribution. Access to optimal light levels and elevated bottom water dissolved inorganic nitrogen concentrations provides selective advantages that may explain phytoflagellate dominance in these estuaries, particularly during the warmer months, when production in surface waters of both systems is strongly N-limited.

EXTENDING THE POSTHARVEST LIFE OF WOODY CUT STEMS

The postharvest life under various handling procedures was determined for nine species of woody cut stems: Buddleja davidii Franch. ‘Royal Red’, Buxus sempervirens L., Hydrangea quercifolia W. Bartram, Ilex crenata Thunb., Ilex L. ‘Nellie R. Stevens’, Ligustrum sinense Lour., Myrica cerifera (L.) Small, Pyracantha coccinea M. Roem., and Viburnum tinus L. ‘Spring Bouquet’. 1-methylcyclopropene (1-MCP) and 50°C distilled (DI) water produced the longest vase life for Buddleja, 6.6 and 6.4 d, respectively, compared to the control of 5.6 d. The 10% sucrose pulse and 1-MCP produced the longest vase life for Viburnum of 15.0 and 13.5 d, respectively, compared to the control of 10.0 d, while vase life of stems placed in 50°C DI and tap water was shorter. Ambient (20°C) DI water was optimal for Myrica (9.9 weeks), while stems pulsed with 10% sucrose had the shortest vase life of 2.2 weeks. Optimum storage (5°C), light level and duration by species were: Buddleja – dark in water for up to 1 week; Buxus – light in water for up to 3 weeks; Hydrangea – cannot be stored; Ilex crenata – light or dark in water for up to 3 weeks; Ilex ‘Nellie R. Stevens’ – light in water for up to 3 weeks; Ligustrum – dark in water for up to 3 weeks; Myrica – either light or dark in water for up to 3 weeks; Pyracantha – any condition for up to 3 weeks and Viburnum – either light or dark in water for up to 1 week. The use of floral foam adversely affected vase life of all species except Buxus. Myrica vase life was longest with 0% sucrose in the vase solution, while Ligustrum, Ilex ‘Nellie R. Stevens’ and Viburnum vase life was longest with either 2 or 4% sucrose. Sucrose in the vase solution had no effect on Buddleja, Buxus, Hydrangea, Ilex crenata or Pyracantha vase life.

Response of Pinus koraiensis seedling growth to different light conditions based on the assessment of photosynthesis in current and one-year-old needles

As one of the three major five-leaved pines in the northern hemisphere, Pinus koraiensis is the most important dominant tree species in the natural mixed-broadleaved Korean pine forests. However, the regeneration of P. koraiensis under the canopy of secondary forest stands is poor because of the light limitation. This study was conducted to understand how P. koraiensis seedlings adapt to different light intensities and what would be the optimum light level for their establishment and growth. Three repetition plots with four light intensities (15%, 30%, 60% and 100% of the natural incident irradiances, achieved by suspending layers of black nylon net above and surrounding the plots) were set up under natural climate conditions in a montane region in eastern Liaoning Province, Northeast China. A total of 80 P. koraiensis seedlings with similar height and root collar diameter were transplanted into four plots. After one year of acclimation to the specific light conditions, the seasonal variations of the photosynthetic variables and needle traits of the current and one-year-old needles, and the growth parameters were observed under four light intensities. The results indicated that: (1) The seedling at 60% treatment exhibited the greatest growth, which agreed with the response of the light-saturated photosynthetic rates (Amax) and the dark respiration rate (Rd) in the current and one-year-old needles, i.e., Rd at 60% treatment was significantly lower than that at 100% treatment, but Amax did not differ between the seedlings at 100% and 60% treatments. (2) The P. koraiensis seedlings have a certain photosynthetic plasticity to adapt the light conditions by adjusting their needle traits and regulating the physiological processes, because Amax, Rd, light saturation point and compensation point, the needle mass area, needle nitrogen and chlorophyll contents were significantly (p<0.05) correlated with the light intensities. Especially, Amax at 100% and 60% treatments was significantly higher (p<0.05) than that at 30% and 15% treatments for both current and one-year-old needles. (3) The needles of different ages played a commutative role during the growing season, i.e., the one-year-old needles played a major role for the photosynthesis in the early growing season; the current year needles did in the later growing season. This ensured the effective photosynthesis throughout the growing season. These findings suggest that P. koraiensis is the in-between heliophilous and shade-tolerant tree species at least for the seedlings up to 8 years.

Early Growth and Physiological Characteristics of Parasenecio firmus by Shading Conditions in Forest Farming

Parasenecio firmus is a perennial plant in Asteraceae, Parasenecio that distributed in Korea, China, and Japan. As dietary style changes for well-being life, consumer demand for functional wild vegetable is increasing. P. firmus has great fragrance and texture and contains caffeoylquinic acid. It has the potential to be further developed as a functional wild vegetable. However, as the natural habitat of P. firmus is quite limited and it should be collected manually in natural stand. So it is need to be a scientific research for artificial cultivation in forest. This study was conducted to investigate the optimum light conditions of P. firmus in forest farming. In this experiment, P. firmus was grown under four different light conditions (50%, 30%, 20%, and 10% of full sunlight) and non-treated (full sunlight). Out of five different shading conditions, P. firmus has shown the best physiological and growth responses to 10% and 20% of full sunlight. There is no statistically significant difference in other shading conditions. At 10% of full sunlight, P. firmus has shown the highest level of statistical significance in the length of shoot, fresh weight of shoot, water contents in all part, SLA (specific leaf area) and LAR (leaf area ratio). It indicates higher water content level, thinner leaf, and wider light-interception areas. On the other hand, at 20% of full sunlight, root color diameter, root length, total fresh weight, total dry weight, leaf area, and chlorophyll contents turned out to be high. It shows that P. firmus is active in chlorophyll activities and carbon dioxide assimilation at even lower light conditions. These results suggest that the optimum light level of P. firmus for artificial cultivation ranges from 10 to 20% of full sunlight. These results can be used as basic data for forest farming.

Motility and photosynthetic responses of the green microalga Tetraselmis subcordiformis to visible and UV light levels

To test the effects of photosynthetic active radiation (PAR, 400–700 nm) and ultraviolet radiation (UVR, 280–400 nm) on phototaxis and photosynthesis of free swimming microalgae, experiments were performed with Tetraselmis subcordiformis (Wille) Butcher under a solar simulator. In particular, we evaluated the effects of different PAR levels and radiation regimes (i.e., PAR only and PAR+UVR) on those two processes. We found that the cells preferred to move to a particular area (e.g., receiving 100 W m−2 PAR) with little photochemical suppression or inhibition of carbon fixation. Adding UV-A to high PAR decreased its swimming capacity and photosynthetic capability, and further adding UV-B led to more inhibition. The suppression of the moving capability of T. subcordiformis was reversible but the cells exposed to PAR combined with UVR needed longer time intervals to recover their motility as compared with those irradiated only with PAR. Based on the above results, we postulate that in nature, the motile capability and photosynthesis of free swimming the green microalga might be impaired by enhanced solar UVR. On the other hand, the cells can reduce the damage caused by high irradiances (and even get the optimum light level for photosynthesis) by a behavioral swimming response.