Internal Light Environment Research Articles

Bacterial community structure of microbial pinnacles in ice-covered Lake Vanda, Antarctica

ABSTRACT The McMurdo Dry Valleys are a cold and arid environment with low biomass relative to most ice-free environments. The ice-covered lakes in the valleys, however, provide a refuge for diverse microbial communities where liquid water persists year-round. Within these lakes, benthic microbial assemblages form ornate structures in the absence of burrowing and grazing organisms. In Lake Vanda, the microbial communities create pinnacles with features including tip, web, and ridge ornaments and brown, green, purple, and beige pigmented zones. Bacterial 16S rRNA gene composition differed between lake depths for all sampled features. Within each depth, community composition correlated with the relative distance into the pinnacle and there were also some significant differences between assemblages in certain zones. The bacterial community composition in the zones may reflect how they respond to environmental changes as the mat is buried, altering the internal light environment and affecting 16S rRNA gene assemblages across niches from the surface to the interior.

Open-Field Agrivoltaic System Impacts on Photothermal Environment and Light Environment Simulation Analysis in Eastern China

In order to clarify the temporal and spatial changes in the internal photothermal environment in an open-field agrivoltaic system (OAVS), this paper took the OAVS in eastern China as the research object and divided the internal area into the southern area, middle area and northern area, according to the spatial structure. Further, a photothermal environment test was conducted in the above three areas in the summer and winter. The results showed that the summer average daylight rate (Rm-avg) in the middle area was 66.6%, while the Rm-avg in the other two areas was about 20%, with no significant difference. In the winter, the light environment in the southern area was slightly better, and the Rm-avg in the above three areas was 26.4%, 24.7% and 19.7%, respectively. On the whole, the relationship between the thermal environmental factors and the solar radiation intensity was consistent. Further, a 3D model of an OAVS was established using Autodesk Ecotect Analysis 2011, and the internal light environment was simulated. Compared with the measured values, the relative error was less than 10%, which verified the reliability of the OAVS model. Then, the model was used to reveal the temporal and spatial changes in the light environment of the OAVS. The simulation results showed that the daylighting rate in the summer from the ground to the height of the fig canopy inside the system was 20.7% to 61.5%. In the winter, the daylighting rate from the ground to the height of the fig canopy inside the system was 17.7% to 36.4%. The effectiveness of the OAVS in reducing the level of solar radiation intensity depended on the time of day and the angle of the sun. At the spatial scale, due to the strong consumption of light by photovoltaic panels, there was a strong horizontal and vertical light environment gradient inside the system. In conclusion, the photothermal environment research of an OAVS based on Autodesk Ecotect Analysis 2011 can not only provide a basis for agricultural production and structural design such as span, height and the laying density of PV panels, but also expand its application to regions with different latitudes and longitudes and specific climates.

Modeling the radiative, thermal and chemical microenvironment of 3D scanned corals

Reef building corals are efficient biological collectors of solar radiation and consist of a thin stratified tissue layer spread over a light scattering calcium carbonate skeleton surface that together construct complex three dimensional (3D) colony structures forming the foundation of coral reefs. They exhibit a vast diversity of structural forms to maximize photosynthesis of their dinoflagellate endosymbionts (Symbiodiniaceae), while simultaneously minimizing photodamage, offer resistance to hydrodynamic stress, reduce attack by predators and increase prey capture and heterotrophic feeding. The symbiosis takes place in the presence of dynamic gradients of light, temperature and chemical species that are affected by the interaction of incident irradiance and water flow with the coral colony. We developed a multiphysics modelling approach to simulate the microscale spatial distribution of light, temperature and O2 in a coral fragment with its morphology determined by 3D scanning techniques. Model results compared well with spatial measurements of light, O2 and temperature under similar flow and light conditions. The model enabled us to infer the effect of coral morphology and light scattering in tissue and skeleton on the internal light environment experienced by the endosymbionts, as well as the combined contribution of light, water flow and ciliary movement on O2 and temperature distributions in the coral.

Modulation of the symbionts light environment in hospite in scleractinian corals

The upregulation of animal chromoproteins (CPs) during thermal stress produces “colorful” bleached corals that facilitate coral recovery after bleaching. In situ measurements indicate that animal CPs present in coral tissues reduce the elevated internal light environment of the remaining symbionts in bleached or low-pigmented stressed corals. However, there is still a lack of understanding regarding the extent to which animal CPs contribute to modifying the internal light environment of the symbionts in hospite. In this study, we evaluate the effect of three animal CPs on the optical properties of the coral tissue and their internal light environment using a numerical model. The model allows estimations of the absorbance spectra of corals as a function of changes in symbiont and animal pigmentation, as well as descriptions of the light environment in hospite of the symbionts. These descriptions were derived from the quantification of the contribution of each pigment component to light absorption, together with the contribution of the coral skeleton’s reflectance. Simulations indicate that animal CPs upregulation modifies the spectral distribution and the intensity of the internal light field. Animal CPs can reduce up to 11% of the light intensity in hospite when present individually, and up to 24% when present in combination. Such reduction may play a critical role in preventing the full development of the bleached phenotype when irradiance rises to excessive levels at low coral pigmentation, facilitating coral recovery and symbiont tissue re-colonization after bleaching. Accordingly, coral’s CPs components need to also be considered when selecting coral species for future restoration efforts.

Green fluorescent protein-like pigments optimise the internal light environment in symbiotic reef-building corals.

Pigments homologous to the green fluorescent protein (GFP) have been proposed to fine-tune the internal light microclimate of corals, facilitating photoacclimation of photosynthetic coral symbionts (Symbiodiniaceae) to life in different reef habitats and environmental conditions. However, direct measurements of the in vivo light conditions inside the coral tissue supporting this conclusion are lacking. Here, we quantified the intra-tissue spectral light environment of corals expressing GFP-like proteins from widely different light regimes. We focus on: (1) photoconvertible red fluorescent proteins (pcRFPs), thought to enhance photosynthesis in mesophotic habitats via wavelength conversion, and (2) chromoproteins (CPs), which provide photoprotection to the symbionts in shallow water via light absorption. Optical microsensor measurements indicated that both pigment groups strongly alter the coral intra-tissue light environment. Estimates derived from light spectra measured in pcRFP-containing corals showed that fluorescence emission can contribute to >50% of orange-red light available to the photosynthetic symbionts at mesophotic depths. We further show that upregulation of pink CPs in shallow-water corals during bleaching leads to a reduction of orange light by 10-20% compared to low-CP tissue. Thus, screening by CPs has an important role in mitigating the light-enhancing effect of coral tissue scattering and skeletal reflection during bleaching. Our results provide the first experimental quantification of the importance of GFP-like proteins in fine-tuning the light microclimate of corals during photoacclimation.

The identity of architectural and lighting solutions of stone mosques of the late XVIII – early XX centuries in Kazan

The work aims to analyze the influence of translucent fences on the light environment in the prayer hall and internal premises with the traditional volumetric-spatial solution of stone mosques of the late XVIII - early ХХ centuries in Kazan (Republic of Tatarstan, Russia). Based on the study of stone mosques in Kazan it was revealed that the main factor was the creation of a complete architectural image of the mosque following the temporary style and solution of the internal light environment through windows and stained-glass windows. Windows and stained-glass windows were scaled using architectural elements and decor for the holistic perception of the object. The significance of the obtained results for architecture is to present recommendations for the organic use of the studied techniques and methods of work on the objects of the architectural heritage in the restoration and design of modern mosques.

Relationship between Acropora millepora juvenile fluorescence and composition of newly established Symbiodinium assemblage.

Coral-dinoflagellate symbiosis is the key biological interaction enabling existence of modern-type coral reefs, but the mechanisms regulating initial host–symbiont attraction, recognition and symbiont proliferation thus far remain largely unclear. A common reef-building coral, Acropora millepora, displays conspicuous fluorescent polymorphism during all phases of its life cycle, due to the differential expression of fluorescent proteins (FPs) of the green fluorescent protein family. In this study, we examine whether fluorescent variation in young coral juveniles exposed to natural sediments is associated with the uptake of disparate Symbiodinium assemblages determined using ITS-2 deep sequencing. We found that Symbiodinium assemblages varied significantly when redness values varied, specifically in regards to abundances of clades A and C. Whether fluorescence was quantified as a categorical or continuous trait, clade A was found at higher abundances in redder juveniles. These preliminary results suggest juvenile fluorescence may be associated with Symbiodinium uptake, potentially acting as either an attractant to ecologically specific types or as a mechanism to modulate the internal light environment to control Symbiodinium physiology within the host.

Improvement of the internal light environment on the objects of transport infrastructure with aid of sun-protective devices

The article analyzes the problems of outdoor stationary sun-protective devices (S.P.D.) and their influence on the natural daylighting levels in the premises of civil objects of transport infrastructure under the hot and sunny climatic conditions of the environment. It is noted, that with clear sky, typical for the said climate, non-uniform luminance of the sky differs seriously from the luminance of standard overcast sky with diffused light, recommended by C.I.E. (Commission International D’Eclairage).A conclusion is made, that with clear sky conditions, a sun-protective devices in the form of stationary canopies (awninas) help to improve the lighting environment in the premises considered. This becomes possible due to reflected sun flow from the surfaces of SPD employed, as well as due to rise of a daylight factor values in farmost from windows zones of interiors, because of the increase of luminance factor values of the sky areas, observed from these zones. Thus, the SPD considered, in the hot and sunny climatic conditions are able not only to carry out their main function of passive method of solar radiation and thermal control in the interiors, but also to act as an efficient measure to improve lightning environment of the premises in question.

The influence of leaf anatomy on the internal light environment and photosynthetic electron transport rate: exploration with a new leaf ray tracing model.

Leaf photosynthesis is determined by biochemical properties and anatomical features. Here we developed a three-dimensional leaf model that can be used to evaluate the internal light environment of a leaf and its implications for whole-leaf electron transport rates (J). This model includes (i) the basic components of a leaf, such as the epidermis, palisade and spongy tissues, as well as the physical dimensions and arrangements of cell walls, vacuoles and chloroplasts; and (ii) an efficient forward ray-tracing algorithm, predicting the internal light environment for light of wavelengths between 400 and 2500nm. We studied the influence of leaf anatomy and ambient light on internal light conditions and J The results show that (i) different chloroplasts can experience drastically different light conditions, even when they are located at the same distance from the leaf surface; (ii) bundle sheath extensions, which are strips of parenchyma, collenchyma or sclerenchyma cells connecting the vascular bundles with the epidermis, can influence photosynthetic light-use efficiency of leaves; and (iii) chloroplast positioning can also influence the light-use efficiency of leaves. Mechanisms underlying leaf internal light heterogeneity and implications of the heterogeneity for photoprotection and for the convexity of the light response curves are discussed.

The optical, absorptive and chlorophyll fluorescence properties of young stems of five woody species

To reveal the roles of stems in responding to the surrounding light environment, the optical properties of stem tissues of five woody species and their effect on bark, xylem and pith photosynthesis were investigated. Species-specific bark morphology and the distribution of pigments along the stem cross-section altered the radial conduction of light to a different degree, but in all investigated species light gradients within stems were markedly steep and visible light was largely depleted within the outer bark and cortex of the stems. Thereby, optical properties of the outer and inner bark resulted in an internal light environment, which is very different from outside according to intensity and spectral composition. Among species PAR-transmittance of outer bark or periderm varied in quantity between mean values of 8.5 and 42% and PAR-transmittance of total bark between 2.2 and 6.2%. The blue-band of the spectrum was totally absorbed by the outer and inner bark tissues. In the red-band total bark transmittance varied between 2 and 11%. Thus, blue light can only trigger photosynthetic electron transport in the cell layers of the cortex near the stem surface, whereas in the underlying cell layers of the xylem or pith the energy for photosynthesis can only be provided by longer wavelengths (green and particularly red light). In all species, the internal light gradient matched well with the chlorophyll fluorescence properties of the respective stem tissues. The maximum and effective quantum efficiencies of PSII clearly decreased from the cortex toward the innermost stem tissues (xylem, pith), which showed also a lower capability of photosynthetic electron transport of PSII. Our results indicate not only that light signals can enter the interior of stems and are modified in quantity and quality by its path through the stem. There is evidence to suggest that the light regime within stems has also profound effects on plastid differentiation and thus the photosynthetic properties of the respective stem tissues.

Green fluorescent protein regulation in the coral Acropora yongei during photoacclimation

Reef-building corals inhabit high light environments and are dependent on photosynthetic endosymbiotic dinoflagellates for nutrition. While photoacclimation responses of the dinoflagellates to changes in illumination are well understood, host photoacclimation strategies are poorly known. This study investigated fluorescent protein expression in the shallow-water coral Acropora yongei during a 30 day laboratory photoacclimation experiment in the context of its dinoflagellate symbionts. Green fluorescent protein (GFP) concentration measured by Western blotting changed reversibly with light intensity. The first 15 days of the photoacclimation experiment led to a ∼1.6 times increase in GFP concentration for high light corals (900 μmol quanta m⁻² s⁻¹) and a ∼4 times decrease in GFP concentration for low light corals (30 μmol quanta m⁻² s⁻¹) compared with medium light corals (300 μmol quanta m⁻² s⁻¹). Green fluorescence increased ∼1.9 times in high light corals and decreased ∼1.9 times in low light corals compared with medium light corals. GFP concentration and green fluorescence intensity were significantly correlated. Typical photoacclimation responses in the dinoflagellates were observed including changes in density, photosynthetic pigment concentration and photosynthetic efficiency. Although fluorescent proteins are ubiquitous and abundant in scleractinian corals, their functions remain ambiguous. These results suggest that scleractinian corals regulate GFP to modulate the internal light environment and support the hypothesis that GFP has a photoprotective function. The success of photoprotection and photoacclimation strategies, in addition to stress responses, will be critical to the fate of scleractinian corals exposed to climate change and other stressors.

Multiple light scattering and absorption in reef-building corals

We present an experimental and numerical study of the effects of multiple scattering on the optical properties of reef-building corals. For this, we propose a simplified optical model of the coral and describe in some detail methods for characterizing the coral skeleton and the layer containing the symbiotic algae. The model is used to study the absorption of light by the layer of tissue containing the microalgae by means of Monte Carlo simulations. The results show that, through scattering, the skeleton homogenizes and enhances the light environment in which the symbionts live. We also present results that illustrate the modification of the internal light environment when the corals loose symbionts or pigmentation.

Internal axial light conduction in the stems and roots of herbaceous plants

In order to reveal any roles played by stems and roots of herbaceous plants in responding to the surrounding light environment, the optical properties of the stem and root tissues of 18 herbaceous species were investigated. It was found that light was able to penetrate through to the interior of the stem and was then conducted towards the roots. Light conduction was carried out within the internodes and across the nodes of the stem, and then in the roots from the tap root to lateral roots. Light conduction in both the stem and root occurred in the vascular tissue, usually with fibres and vessels serving as the most efficient axial light conductors. The pith and cortex in many cases were also involved in axial light conduction. Investigation of the spectral properties of the conducted light made it clear that only the spectral region between 710 nm and 940 nm (i.e. far-red and near infra-red light) was the most efficiently conducted in both the stem and the root. It was also found that there were light gradients in the axial direction of the stem or root, and the light intensity generally exhibited a linear attenuation in accord with the distance of conduction. These results revealed that tissues of the stem and root are bathed in an internal light environment enriched in far-red light, which may be involved in phytochrome-mediated metabolic activities. Thus, it appears that light signals from above-ground directly contribute to the regulation of the growth and development of underground roots via an internal light-conducting system from the stem to the roots.

TEMPERATURE AND IRRADIANCE EFFECTS ON GROWTH OF PITHOPHORA OEDOGONIA (CHLOROPHYCEAE) AND SPIROGYRA SP. (CHAROPHYCEAE)1

ABSTRACT Growth responses of Pithophora oedogonia (Mont.) Wittr. and Spirogyra sp. to nine combinations of temperature (15°, 25°, and 35°C) and photon flux rate (50, 100, and 500 μmol·m−2·s−1) were determined using a three‐factorial design. Maximum growth rates were measured at 35°C and 500 pmol·m−2·s−1 for P. oedogonia (0.247 d−1) and 25°C and 500 μmol·m−2·s−1 for Spirogyra sp. (0.224 d−1). Growth rates of P. oedogonia were strongly inhibited at 15°C (average decrease= 89%of maximum rate), indicating that this species is warm stenothermal. Growth rates of Spirogyra sp. were only moderately inhibited at 15° and 35°C (average decrease = 36 and 30%, respectively), suggesting that this species is eurythermal over the temperature range employed. Photon flux rate had a greater influence on growth of Spirogyra sp. (31% reduction at 50 pmol·m−2·s−1 and 25°C) than it did on growth of P. oedogonia (16% reduction at 50 μmol·m−2·s−1 and 35°C). Spirogyra sp. also exhibited much greater adjustments to its content of chlorophyll a (0.22–3.34 μg·mg fwt−1) than did P. oedogonia (1.35–3.08 μg·mg fwt−1). The chlorophyll a content of Spirogyra sp. increased in response to both reductions in photon flux rate and high temperatures (35°C). Observed species differences are discussed with respect to in situ patterns of seasonal abundance in Surrey Lake, Indiana, the effect of algal mat anatomy on the internal light environment, and the process of acclimation to changes in temperature and irradiance conditions.

A Comparative Study of Internal Light Environment in Bifacial Leaves of Different Plants

Parameters of light propagation in plant leaves — absorption and scattering coefficients, asymmetry of scattering — have been estimated on the basis of measured transmission and emission as well as internal fluxes. This estimation has been carried through by solving the inverse problem of the 4-flux radiative transfer — a theory considering forward and backward diffuse as well as directed components of the overall radiation in a multiple scattering sample. Using the gained parameters, light flux gradients in a two-layered model leaf have been calculated at different wavelengths. Monte Carlo simulation of absorption spectra performed with the parameters obtained with this treatment is in a good agreement with experimental spectra, thus substantiating the theory. Parallel calculations with the two-flux (Kubelka-Munk) theory provide an estimation of the accuracy and applicability of this more simple treatment. Calculations have been performed for three different plants: Catalpa bignonioides, Tilia americana and Vitis riparia.

LIGHT ABSORPTION BY PLANTS AND ITS IMPLICATIONS FOR PHOTOSYNTHESIS

LIGHT ABSORPTION BY PLANTS AND ITS IMPLICATIONS FOR PHOTOSYNTHESIS