Reduced Light Intensity Research Articles

Are portable polyethylene tents reliable for imposing heat treatments in field-grown wheat?

Environmental variability has increased in recent decades and there are high expectations that heat waves will affect wheat productivity. Therefore, methods to quantify the effects of high temperature on wheat growth, yield, and yield-related traits under field conditions are greatly needed. In this opinion paper, we first describe the different approaches to quantify these effects, briefly highlighting their pros and cons. Portable polyethylene tents over the plots are cost-effective and convenient when relatively large plots are preferred and/or when there is no access to electricity in the field. This method shares a drawback with other approaches due to the tent reducing light intensity and altering other environmental factors like wind, humidity and evapotranspiration. We discuss to what degree there is an actual confounding effect (incorrectly assigning changes to heat effects that might be in part due to lower radiation). In that context, we not only discuss the issue theoretically, but also present results from a field experiment comparing a control (open uncovered plot), and a “roof-only” treatment (covering the plot with a polyethylene roof alone; thus impacting incoming radiation but not temperature). These treatments were imposed at either booting or the onset of grain filling, and testing two wheat cultivars having contrasting grain numbers per m2 and average grain weight. Supporting a theoretical framework that this reduced radiation would be compensated by increased radiation use efficiency, we show empirically that the roof-only treatment (which reduced incoming photosynthetically active radiation by 10.7 ± 0.2 % at noon on sunny days, but did not alter the temperature at any time of the day) did not result in any yield penalty with respect to the uncovered control plots. Thus, portable polyethylene tents are a reliable method to impose heat treatments in field experiments. Although other methods are more sophisticated and may be perceived as having fewer confounding factors, portable polyethylene tents are ideally suited to irrigated field experiments where electricity is not available, where relatively large plots are needed, and for research carried out on a limited budget.

Lux study: Contribution of a three-dimensional, high dynamic range, ultra-high-definition heads-up visualization system to a significant delivered light intensity decrease during different types of ocular surgeries

To explore the hypothesis that using a large, three-dimensional (3D), ultra-high-definition (4K), heads-up display (HUD) system in a real-life setting may be associated with a significant reduction in light intensity (LI) delivered during various types of eye surgery. Single center, post-learning curve observational study of 142 independent consecutive cases: 73 cataracts and 69 vitrectomies (VR). For each group, the only variable setting was the LI. The LI delivered by each source was calibrated in lumens (lm). In the VR group, the delivered LI dramatically decreased from the 80% reference to 27.8%±13.2% (P<0.0001) (4.3 to 1.5lm). Among these surgeries, 91.3% needed 40% or less LI (2.3lm). The corneal transparency and quality of pupil dilation showed some correlation with the results. In the cataract group, the difference was even more spectacular, from 80% to 15%±11.3% (P<0.0001) (2.5 to 0.3lm). Among these surgeries, 80.8% required less than 20% LI (0.5lm). The surgical time, LI variations and type of cataract seemed to influence the results, down to 9.6%±5.4% (P<0.0001) (0.22lm) for nuclear cataracts, which represented 63% of the cataract sample. The digital signal amplification with this HUD system allows comfortable posterior as well as anterior segment surgery despite the decrease in incident light, suggesting an unprecedented reduction in the risk of phototoxicity compared to conventional systems as well as a likely improvement in patient comfort.

Biochemical and physiological changes in conilon coffee (Coffea canephora) grown under different levels of irradiance

Modern agriculture values the most sustainable and dynamic means of production, which can be promoted through the association between coffee and tree components, aiming at the best use of the land. However, within our understanding of the physiological and biochemical behaviors of the coffee tree, the irradiance limiting conditions are crucial to maximize the potential gains generated in these systems. In this sense, the objective of this study was to evaluate the effects of different levels of irradiance restriction on the physiological and biochemical characteristics of two genotypes of Conilon coffee. The experiment was conducted in a 2 × 3 factorial scheme, corresponding to two Conilon coffee clones and three levels of light intensity restriction (0, 30 and 50%), in a randomized block design with four replications. The synthesis of total chlorophyll b and the leaf N content of the genotypes CL6 and CL12 increased with the reduction of light. On the other hand, there was a reduction in the levels of carbohydrates, amino acids and phenols with the reduction of light intensity. Restricted levels of irradiance caused different changes in the physiological and biochemical characteristics of the studied genotypes, showing genetic divergences between them

Biologically Relevant Lighting: An Industry Perspective.

Innovations in LED lighting technology have led to tremendous adoption rates and vastly improved the metrics by which they are traditionally evaluated–including color quality, longevity, and energy efficiency to name a few. Additionally, scientific insight has broadened with respect to the biological impact of light, specifically our circadian rhythm. Indoor electric lighting, despite its many attributes, fails to specifically address the biological responses to light. Traditional electric lighting environments are biologically too dim during the day, too bright at night, and with many people spending much of their lives in these environments, it can lead to circadian dysfunction. The lighting industry’s biological solution has been to create bluer days and yellower nights, but the technology created to do so caters primarily to the cones. A better call to action is to provide biologically brighter days and biologically darker nights within the built environment. However, current lighting design practices have specified the comfort and utility of electric light. Brighter intensity during the day can often be uncomfortable or glary, and reduced light intensity at night may compromise visual comfort and safety, both of which will affect user compliance. No single lighting solution will effectively create biologically brighter days and biologically darker nights, but rather a variety of parameters need to be considered. This paper discusses the contributions of spectral power distribution, hue or color temperature, spatial distribution, as well as architectural geometry and surface reflectivity, to achieve biologically relevant lighting.

Low Light Availability Reduces the Subsurface Sediment Carbon Content in Halophila beccarii From the South China Sea.

Eutrophication, dredging, agricultural and urban runoffs, and epiphyte overgrowth could reduce light availability for seagrass. This may affect “blue carbon” stocks in seagrass beds. However, little research is available on the effect of light intensities on carbon sequestration capacity in seagrass beds, especially small-bodied seagrasses. The dominant seagrass Halophila beccarii, a vulnerable species on the IUCN Red List, was cultured in different light intensities to examine the response of vegetation and sediment carbon in seagrass beds. The results showed that low light significantly reduced leaf length and above-ground biomass, while carbon content in both above-ground and below-ground tissues were not affected. Low light reduced both the above-ground biomass carbon and the total biomass carbon. Interestingly, while under saturating light conditions, the subsurface and surface carbon content was similar, under low light conditions, subsurface sediment carbon was significantly lower than the surface content. The reduction of subsurface sediment carbon might be caused by less release flux of dissolved organic carbon from roots in low light. Taken together, these results indicate that reduced light intensities, to which these meadows are exposed to, will reduce carbon sequestration capacity in seagrass beds. Measures should be taken to eliminate the input of nutrients on seagrass meadows and dredging activities to maintain the “blue carbon” storage service by enhancing light penetration into seagrass.

Implications of Wound Healing on Subcutaneous Photovoltaic Energy Harvesting.

Cardiac pacemakers must be regularly replaced due to depleted batteries. A possible alternative is proposed by subcutaneous photovoltaic energy harvesting. The body's reaction to an implant can cause device encapsulation. Potential changes in spectral light transmission of skin can influence the performance of subcutaneous photovoltaic cells and has not yet been studied in large animal studies. Subcutaneous implants measuring changes in the light reaching the implant were developed. Three pigs received those implants and were analyzed for seven weeks. Spectral measurements with known irradiation were performed to identify possible changes in the transparency of the tissues above the implant during the wound healing process. A histological analysis at the end of the trial investigated the skin tissue above the subcutaneous photovoltaic implants. The implants measured decreasing light intensity and shifts in the light's spectrum during the initial wound healing phase. In a later stage of tissue recovery, the implants measured a generally reduced light intensity compared to the healthy tissue after implantation. The spectral distribution of the measured light at the end of the trial was similar to the first measurements. The histological analysis showed subcutaneous granulation tissue formation for all devices. The varying reduction of light intensity reaching the implants means that safety margins must be sufficiently high to ensure the power. At the end of the wound healing process, the spectral distribution of the light reaching the implant is similar to healthy tissue. Optimizations of spectral sensitivity of photovoltaic cells are possible.

Incoherent Optical Tweezers on Black Titanium.

Optical tweezers enable the manipulation of micro- and nanodielectric particles through entrapment using a tightly focused laser. Generally, optical trapping of submicron size particles requires high-intensity light in the order of MW/cm2. Here, we demonstrate a technique of stable optical trapping of submicron polymeric beads on nanostructured titanium surfaces (black-Ti) without the use of lasers. Fluorescent polystyrene beads with a diameter d = 20-500 nm were successfully trapped on black-Ti by low-intensity focused illumination of incoherent light at λ = 370 m from a Hg lamp. Light intensity was 5.5 W/cm2, corresponding to a reduced light intensity of 6 orders of magnitude. Upon switching off illumination, trapped particles were released from the illuminated area, indicating that trapping was optically driven and reversible. Such trapping behavior was not observed on nonstructured Ti surfaces or on nanostructured silicon surfaces. Thus, the Ti nanostructures were demonstrated to play a key role.

Comparative Assessment of Hydroponic Lettuce Production Either under Artificial Lighting, or in a Mediterranean Greenhouse during Wintertime

Butterhead lettuce was grown hydroponically in a vertical farm under high (HLI) and low (LLI) light intensity (310, and 188 μmol m−2 s−1, respectively) and compared to hydroponically grown lettuce in a greenhouse (GT) during wintertime in Athens, Greece (144 μmol m−2 s−1). The highest plant biomass was recorded in the HLI treatment, whereas LLI and GT produced similar plant biomass. However, the LLI produced vortex-like plants, which were non-marketable, while the plants in the GT were normal-shaped and saleable. Net photosynthesis was highest in the HLI and higher in the LLI than in the GT, thereby indicating that light intensity was the dominant factor affecting photosynthetic performance. Nevertheless, the unsatisfactory performance of the LLI is ascribed, not only to reduced light intensity, but also to reduced light uniformity as the LED lamps were closer to the plants than in the HLI. Furthermore, the large solar irradiance variability in the GT resulted in substantially higher adaptation to the increased light intensity compared to LLI, as indicated by chlorophyll fluorescence measurements. Light intensity and photoperiod are believed to be the primary reasons for increased nitrate content in the GT than in the vertical farming treatments.

Apple tree adaptation to shade in agroforestry: an architectural approach.

The expression of shade adaptation traits is expected to be stronger in low light and can be detrimental to flowering and yield. Our study focused on the expression of shade adaptation traits of apple trees (Malus domestica Borkh. 'Dalinette') in an agroforestry system. The architecture of 45 apple trees in their third and fourth year was extensively described and analyzed at the tree scale and compared depending on the light quantity received during the growing season. Flower cluster phenology and the relation between leaf area and floral initiation were also investigated. The number of growing shoots and the leaf area were reduced by shade even if specific leaf area increased with increasing shade. Shade did not modify primary growth but did decrease secondary growth, so that apple tree shoots in shade were slender, with a lower taper and reduced number and proportion of flower clusters. The correlation between floral initiation and leaf area was high both in full and moderate light but not for apple trees in low light. Shade did not impact the date of bud burst and the early phenological stages of flower clusters, but it reduced the number of days at full bloom. Our results suggest that while the architecture of apple trees is modified by a reduction in light intensity, it is not until a reduction of 65% that the capability to produce fruit is impeded. These results could help optimize the design of apple-tree-based agroforestry systems.

Pengendalian Gulma Dengan Tanaman Sela Kacang Pada Budidaya Jagung Manis Tumpangsari

An research on weed control with legumes in sweet corn intercropping was conducted in Kasihan, Bantul District of Yogyakarta on February to June 2003. The experiment was aimed to study the role of legume crop to control weed growth in the intercropping of sweet corn. The experiment was arranged in a single factor randomized completely block design (RCBD) with three blocks as replication. The treatment was the kind of legumes i.e groundnut, mungbean and soybean planted with sweetcorn in the ratio of 1: 1, 1:2, and 1:3 to be compared to sole crop of sweet com and legumes. The result of this experiment showed that legumes existence reduced light intensity on soil surface. Presence of legumes as second crop with ratio up to 1:3 was significantly reduced the weed growth but not significantly influenced growth and yield of sweet corn. The higher the ratio of sweet corn-legumes, the achievement of legumes yield and land equivalent ratio were higher.

The Effect of Plastic Waste Attachment on Branching Coral to Zooxanthellae Abundance in the Kelapa Dua Island Waters, Seribu Islands

HighlightLight intensity from plastic waste was positively correlated with the abundance of zooxanthellae in corals.The abundance of zooxanthellae between sack plastic and clear plastic treatment tended to be the same.The treatment of packaging plastic was treated with the lowest light intensity.The treatment of black plastic was the treatment that produced the lowest abundance of zooxanthellae. AbstractCoral growth in Indonesia was being disrupted due to the continued threat of environmental change, such as littering to the beach. This study aimed to analyze the effect of the attachment of different colored plastic waste to the rate of zooxanthellae abundance on branching corals in Kelapa Dua Island waters. Branching coral colony samples consisted of the genus Acropora and Porites with a total of 15 fragments of coral colonies at the depth of 80-90 cm were tested with a treatment of the attachment plastic wastes (control, clear plastic, plastic sack, plastic packaging, and black plastic) for four days. The zooxanthellae abundance was calculated using the APHA (American Public Health Association) formula. The results of zooxanthellae abundance on the closure treatment of branching coral samples with black plastic and control had the lowest and highest values by 4.25 x 105 cells/cm2 and 1.38 x 106 cells/cm2. The results of the linear regression test showed that there was a significant relationship between plastic waste with low light intensity and a decrease of zooxanthellae abundance in coral colonies with the equation Y of 972.78x + 653402, determination index (R2) of 0.68, and correlation index (r) of 0.83. These results indicated that the attachment of plastic waste to branching coral colonies could be a stressor on coral animals in reducing light intensity, which caused a reduction of zooxanthellae abundance as coral endosymbiont.

Study of Microbending Loss Single Mode Optic Fiber in Sand Powder Against Pressure

Research has been carried out to further investigate specifically the effect of sand powder, both the size of the sand grains and the thickness of the sand powder on the photodetector output as an advanced study of the single-mode optical fiber microbending loss theory in sand grains to pressure. This was done to investigate the response of optical fibers due to microbending loss to the load and determine the size of the sand particles that are most effectively used as a compiler of load sensors. The principle works to test the response of load sensors based on single-mode fiber optic microbending loss in the form of photodetector output when given a large variety of pressure. The method used in this research is to observe the reduction in the intensity of the light transmitted through optical fibers in the form of a voltage drop that is read by MMD that is connected to the photodetector. The reduced light intensity shows that the load sensor experiences optical attenuation of the laser as a light source with a wavelength of 1550 nm and a power of 1.47 mW. Microbending loss is caused by mechanical pressure that can change the direction of optical signal transmission and the radius of the curve is equal to or less than the diameter of a bare optical fiber. Observations were made using 12 load sensors with variations in the size of the sand grains in each diameter of the hose. The results of this study obtained the size of the most effective grains of sand providing microscopic curvature in the optical fiber that is 0.05 mm in terms of the correlation between the response of sensors with various diameters to changes in pressure.

Decreased low-light regulates plant morphogenesis through the manipulation of hormone biosynthesis in Solanum lycopersicum

Low light intensity limits the growth and development of plants. How plant morphogenesis and adaptation are generated in response to reduced low-light are important for tomato plants. To investigate the light-dependent and long-term adapted regulations on tomato plants, four simulations of gradually reduced light intensity (LI), referred to as 100 % LI, 80 % LI, 67 % LI, and 40 % LI, are designed and performed in four-week-old tomato plants for two more weeks. We find that plant biomass was decreased in response to the reduced light intensity. Interestingly, the stem diameters, internode lengths, light- and CO2- response curves, maximum velocity of RuBP carboxylation by Rubisco (Vcmax), and the maximum potential rate of electron transport contributing to RuBP regeneration (Jmax) are largely affected in 40 % LI, but slightly changed in 80 % LI treatments when compared to 100 % LI control, suggesting moderately decreasing the light intensity did not substantially influence the growth and morphological phenotypes of tomato plants. The mRNA-seq results indicate that the differentially expressed genes (DEGs) are mainly enriched in the pathways corresponding to signal transductions and biosynthesis of plant hormone. We further find that the contents of jasmonic acid (JA), salicylic acid (SA) and zeatin (ZT) are significantly decreased, while content of aminocyclopropane-1-carboxylic acid (ACC) are increased in the plants treated with decreased and low light. Our results present a hypothesis that ZT functions in the regulating the plant stem diameter and internode length in decreased low-light treatments. Our study indicates that multiple plant hormones direct the morphogenesis and adaption in tomato plants in response to reduced low-light environment by manipulation of hormone biosynthesis. Hence, this study updates the understanding of formation of plant morphogenesis and regulation of endogenous hormones in the long-term adapted plants grown under decreased low-light environmental condition.

Study on the Effect of Shading on Performance of Leafy Vegetables

A field experiment was conducted at Sher-e-Bangla Agricultural University, Sher-e-Bangla, Dhaka, Bangladesh during the period from March, 2019 to June, 2019. The aim of the study was to select best summer leafy vegetables, suitable for holding under different shade condition in agroforestry systems. The selected vegetables were also grown in control i.e., open field condition or in full sunlight. The vegetables were Indian Spinach, Stem Amaranth, and Red Amaranth and treatments were T0= planting summer leafy vegetables under full sunlight, T1= planting summer leafy vegetables under 50% shade condition (reduced light intensity) and T2 = planting summer leafy vegetables under 75% shade condition (reduced light intensity). The experiment was laid out following single factor RCBD design. Three replications were used for each treatment for each crop. During the study period maximum light intensity reduction was recorded in Red Amaranth (48.28%) in 75% shade condition and minimum light intensity was reduced in case of Indian Spinach (26.14%) under 50% shade condition. The reduced light intensity had substantial effects on various growth parameters of the summer leafy vegetables. From the experiment, significant result was observed in all morphological characteristics for all leafy vegetables under reduced light intensity. Apart from this, highest yield was found in Stem Amaranth (22.33 ton/ha) and Indian Spinach (13.83 ton/ha) in 75% shade condition. Highest yield of Indian Spinach (19.40 ton/ha), Stem Amaranth (27.25 ton/ha) and Red Amaranth (11.30 ton/ha) was recorded under full sunlight. Considering shade condition, Stem Amaranth and Indian Spinach were best suitable for growing in Agroforestry systems.

Identification and analysis of low light tolerant rice genotypes in field conditions and their SSR-based diversity in various abiotic stress tolerant lines

The yield potentiality of kharif rice is not completely used even under well-irrigated agro-ecosystem, mainly due to low irradiance by overcast cloud throughout the growing season in eastern India. We observed more than 50% yield reduction compared to the performance of 100 high-yield genotypes for consecutive three years both under open and 30-35% reduced light intensity, mainly by 34%, 25% and 12% reduction of panicle number, grains per panicle and test weight. As per the analysis of variance, genotypic variance explained 39% of the total yield-variation under shade with 58% heritability. Overall, the maintenance of equal panicle per plant in both open and shade has the highest association with shade tolerance. Purnendu, Sashi and Pantdhan19 showed less than 28% yield-reduction by maintenance or even by increasing grain numbers under shade and test weight. On the other hand, maintenance of an equal number of panicle under both situations was the key to the tolerance of Bhasamanik, Sasarang, Rudra and Swarnaprabha. As compared to open, we noticed the improvement of chlorophyll a and b under shade but saw a poor correlation with the shade tolerance index. Comparing the net photosynthesis rate (Pn) in eight genotypes, we found the best tolerant line ranked last with least Pn at low light intensity (400 μmol m-2 s-1). We also identified diverse parental combinations between newly identified shade tolerant and abiotic stress tolerant high-yielding rice lines following diversity analysis using 54 simple-sequence repeats. Thus, the selected tolerant lines from a large set of genotypes with different adjustment ability to keep up high yield under low light intensity can be used for physiological, molecular analysis as well as pyramiding of traits.

Intrinsical localization of both topological (anti-kink) envelope and gray (black) gap solitons of the condensed bosons in deep optical lattices.

By developing quasi-discrete multiple-scale method combined with tight-binding approximation, a novel quadratic Riccati differential equation is first derived for the soliton dynamics of the condensed bosons trapped in the optical lattices. For a lack of exact solutions, the trial solutions of the Riccati equation have been analytically explored for the condensed bosons with various scattering length as. When the lattice depth is rather shallow, the results of sub-fundamental gap solitons are in qualitative agreement with the experimental observation. For the deeper lattice potentials, we predict that in the case of as>0, some novel intrinsically localized modes of symmetrical envelope, topological (kink) envelope, and anti-kink envelope solitons can be observed within the bandgap in the system, of which the amplitude increases with the increasing lattice spacing and (or) depth. In the case of as<0, the bandgap brings out intrinsically localized gray or black soliton. This well provides experimental protocols to realize transformation between the gray and black solitons by reducing light intensity of the laser beams forming optical lattice.

Influence of shade intensity on growth, biomass allocation, yield and quality of pineapple in mango-based intercropping system

Fruit tree-based intercropping system is commonly practiced in India; however, optimization of light environment for intercrops is essentially required to enhance their productivity. Influence of three shade intensities were examined on growth, biomass allocation pattern, leaf chlorophyll content, nutrient uptake, fruit yield and quality of pineapple in mango-based intercropping system. Compared to the monoculture pineapple system (LE0), the mean shade intensity under LE1, LE2 and LE3 were 23.8 %, 48.6 % and 73.3 %, respectively, whereas the mean PAR availability was 76.2 %, 51.4 % and 26.7 %, respectively. Significantly higher absolute growth rate (AGR), crop growth rate (CGR) and relative growth rate (RGR) was recorded under medium shade intensity (LE2). Dry matter accumulation was significantly high under LE2 followed by LE3. The biomass accumulation was significantly high in leaf followed by fruit and stem, whereas root system exhibited minimum biomass accumulation. Biomass of leaf and crown decreased with the plant biomass, whereas the biomass of fruit, stem and sucker increased. Contents of Chl a, Chl b and Chl a + b increased with the shade intensity and were found maximum under LE3. A gradual increase in N and P contents were observed in the leaves of pineapple with the reduction in PAR transmittance. However, the K content was relatively high under LE2. Increased fruit yield, fruit weight and fruit/crown ratio were recorded under moderate shade intensity (LE2). Total soluble solids and sugar content marginally decreased with the reduction in light intensity, whereas titratable acidity increased. Sunburn intensity significantly reduced under LE2 and LE3. Path analysis studies indicated that plant biomass was that most important predictor for fruit yield in pineapple. Our findings demonstrate that in eastern tropical region of India pineapple may be cultivated as an intercrop with ∼50 % shade intensity since the performance of crop is significantly affected under monoculture system.

Non-structural carbohydrates and sugar export in grapevine leaves exposed to different light regimes.

Light is a main environmental factor that determines leaf microclimate within the vine, as well as its photosynthesis and carbohydrate metabolism. This study aimed to examine the relationships between photosynthesis, carbohydrate metabolism, and the expression of related genes in leaves of grapevine grown under different radiation regimes. During the 2014/2015 growing season, an experiment was conducted on a Malbec vineyard (Vitis vinifera L.) in which four radiation exposure treatments were established on the leaves: (1) East, (2) West, (3) Sun, and (4) Shade (i.e., reduction in light intensity). Diurnal dynamics of photosynthesis and non-structural carbohydrates were measured and leaf export rates were calculated. Transcript profiles of leaf sugar transporters (VvHT1, VvHT3, VvSUC27), a sucrose phosphate synthase enzyme (VvSPS), and invertases (VvGIN1, VvCWI) were also examined. We showed that East and Sun leaves had higher daily photosynthetic and export rates than West leaves, which was mainly explained by the environmental conditions (air and leaf temperature, VPDleaf-air ) and leaf water status. Shade leaves accumulated less starch and soluble sugars than exposed leaves, which correlated with a higher expression of hexose transporters and invertases. The hypotheses that these sugars in Shade leaves would play a role as signaling molecules and/or have increased sink strength and phloem unloading are discussed. These results allow us to understand the physiological and molecular behavior of leaves exposed to different radiation regimes, which can be used to design appropriate vineyard management practices.

Low light intensities increase avoidance behaviour of diurnal fish species: implications for use of road culverts by fish.

Inadequately designed culverts can be physical barriers to fish passage if they increase the velocity of water flow in the environment, alter natural turbulence patterns or fail to provide adequate water depth. They may also act as behavioural barriers to fish passage if they affect the willingness of fish species to enter or pass through the structure due to altered ambient light conditions. To understand how reduced light intensity might affect fish behaviour in culverts, the authors performed a behavioural choice experiment quantifying the amount of time individual fish spent in dark and illuminated areas of a controlled experimental channel. They found that behavioural responses were largely reflective of the species' diel activity patterns; the diurnal species Craterocephalus stercusmuscarum and Retropinna semoni preferred illuminated regions, whereas the nocturnal/crepuscular Macquaria novemaculeata preferred the darkened region of the channel. Bidyanus bidyanus were strongly rheotactic, and their behaviour was influenced more by water flow direction than ambient light level. The authors then determined that a threshold light intensity of only c. 100-200 lx (cf. midday sunlight c. 100,000 lx) was required to overcome the behavioural barrier in c. 70% of the diurnally active C. stercusmuscarum and R. semoni tested. When these values were placed into an environmental context, 15 road-crossing (3.4-7.0 m long) box (c. 1 m × 1 m, height × width) and pipe (c. 1 m diameter) culverts sampled in Brisbane, Australia, recorded light intensities in the centre of the structure that were below the threshold for C. stercusmuscarum and R. semoni movement and could potentially be a barrier to their passage through the structure. Attention is required to better understand the impacts of low light intensity in culverts on fish passage and to prioritize restoration.

Low light intensity and compost modified biochar enhanced maize growth on contaminated soil and minimized Pb induced oxidative stress

Heavy metal uptake by agricultural crops poses great danger to human health. Application of compost and biochar has been used extensively for metal immobilization in soil and to reduce metal uptake by crop plant. Their efficiency is however, limited by other environmental factors like water and light intensity. In this study, the effects of organic amendments (Mexican Sunflower Compost and Rice Husk (RH) biochar) in combination with varying light intensities on growth and Pb uptake by maize crop grown on industrially contaminated soil containing 53,752 mg/kg Pb was investigated. Compost and biochar were applied singly and in combination at 0, 2.5, 5 and 7.5 t ha−1 while different layers of net were used to vary light intensity (one layer = 60: 386 lx, two layers = 53:340 lx, three layers = 27 %: 177 lx and zero layer with 100 % light intensity of 634 lx served as control). Soil Pb concentration and stress metabolites (Proline and cysteine) production before and after the experiment were also determined. Results showed that, higher rates of organic amendments and reduced light intensity increased the vegetative growth and yield of maize on contaminated soil compared to 100 % light intensity. Combination of biochar and compost performed better than sole application. It reduced post-cropping soil Pb concentration and Pb uptake by maize, especially under low light intensity. The stress metabolites were more in the leaves of maize crop grown in un-amended soil and under 100 % light intensity. Addition of organic amendment coupled with reduction in light intensity therefore, enhanced maize growth on contaminated soil, reduced Pb uptake and oxidative stress, while, heavy metal accumulation and stress metabolites production were more in maize grown in un-amended soil and exposed to high light intensity.