Inclusion of ionizing radiation in a mathematical model for photosynthesis.

Ionizing radiation of astrophysical origin might have played an important role in biological evolution during the long course of Earth's evolution. Several phenomena might have induced intense fluctuations in background ionizing radiation, such as highly energetic stellar explosions. There might also be anthropogenic causes for environmental radiation fluctuations, resulting from nuclear industry activities. The inclusion of these effects in a mathematical model for photosynthesis provides a useful tool to account for the damages of the above-mentioned phenomena in vegetal life. Mathematical models for photosynthesis typically only consider ultraviolet radiation and photosynthetically active radiation, as they have been a ubiquitous physical factor in the settlement of vegetal life. In this work a mathematical model for aquatic photosynthesis is modified, from first principles, to include the action of particulate ionizing radiation on the photosynthetic process. After assuming an ansatz allowing to separate damage/repair kinetics of ultraviolet and ionizing radiations, a treatable mathematical expression of the model is obtained. This generalized model is presented as a function of radiometric and photometric magnitudes, making it prone to calibration and useful to apply to aquatic ecosystems under radiational stress due to gamma-ray bursts, cosmic ray bursts, solar storms, or other sources of ionizing radiations.

Rapid Colonization of Uranium Mining-Impacted Waters, the Biodiversity of Successful Lineages of Phytoplankton Extremophiles.

Anthropogenic extreme environments are emphasized as interesting sites for the study of evolutionary pathways, biodiversity, and extremophile bioprospection. Organisms that grow under these conditions are usually regarded as extremophiles; however, the extreme novelty of these environments may have favor adaptive radiations of facultative extremophiles. At the Iberian Peninsula, uranium mining operations have rendered highly polluted extreme environments in multiple locations. In this study, we examined the phytoplankton diversity, community structure, and possible determining factors in separate uranium mining-impacted waters. Some of these human-induced extreme environments may be able to sustain indigenous facultative extremophile phytoplankton species, as well as alleged obligate extremophiles. Therefore, we investigated the adaptation capacity of three laboratory strains, two Chlamydomonas reinhardtii and a Dictyosphaerium chlorelloides, to uranium-polluted waters. The biodiversity among the sampled waters was very low, and despite presenting unique taxonomic records, ecological patterns can be identified. The microalgae adaptation experiments indicated a gradient of ecological novelty and different phenomena of adaptation, from acclimation in some waters to non-adaptation in the harshest anthropogenic environment. Certainly, phytoplankton extremophiles might have been often overlooked, and the ability to flourish in extreme environments might be a functional feature in some neutrophilic species. Evolutionary biology and microbial biodiversity can benefit the study of recently evolved systems such as uranium-polluted waters. Moreover, anthropogenic extremophiles can be harnessed for industrial applications.

Direct Effects of Temperature on Growth of Different Tropical Phytoplankton Species.

Temperature increase may influence competition among phytoplankton species, potentially intensifying cyanobacteria blooms that can be favored by direct and indirect effects of temperature. In this study, we aimed to clarify how cyanobacteria can be favored by the direct effects of increased temperature compared to diatoms and chlorophytes. Strains of the most representative species of a eutrophic coastal lagoon (Microcystis aeruginosa, Planktothrix agardhii, Desmodesmus communis, and Cyclotella meneghiniana) were used to test the hypothesis that cyanobacteria would be favored by the direct effect of temperature increase. First, we evaluated the effect of temperature increase on growth in monocultures (batch and chemostats) at 25 and 30 °C and after in mixed cultures (chemostats). In batch monocultures, the cyanobacteria showed higher growth rates in 30 °C than in 25 °C. However, in continuous culture experiments (chemostats), growth rates of M. aeruginosa and P. agardhii were not affected by temperature, but the strains showed higher biovolume in steady-state with the temperature increase. In continuous mixed cultures, M. aeruginosa was always dominant and C. meneghiniana was excluded, regardless of temperature tested. D. communis was able to coexist with lower biomass. This study shows that rising temperatures can be detrimental to diatoms, even for a tropical strain. Although some studies indicate that the dominance of cyanobacteria in warmer climates may be due to the indirect effect of warming that will promote physical conditions in the environment more favorable to cyanobacteria, the outcomes of mixed cultures demonstrate that the direct effect of temperature can also favor the dominance of cyanobacteria.

Seasonal dependency of controlling factors on the phytoplankton production in Taihu Lake, China.

In this study, 44 profiles of gross primary productivity (GPP) and sunlight, along with water temperature, Chlorophyll-a (Chla) and nutrients, were observed in Meiliang Bay of Taihu Lake, China, in the spring, summer, and fall seasons. Effects of water temperature, light, and nutrient concentration were examined in relation to the GPP-unit-Chla (GPP of algae per Chla). The results showed that the optimum temperature for the GPP of phytoplankton was 27.9°C, the optimal PNA-unit-Chla (photon number absorbed by phytoplankton per Chla) was 0.25 (mol), and the HSCN-unit-Chla and HSCP-unit-Chla (half-saturation constants of nitrogen and phosphorus of algae per Chla) were 0.005 (mg/L) and 0.0004 (mg/L), respectively. The seasonal dependency of the effect of different factors on the GPP was analyzed. Compared with temperature and nutrients, light was found to be the most important factor affecting the GPP during the three seasons. The effect of temperature and nutrients on the GPP of phytoplankton has obvious seasonal change. In spring, temperature was the secondary factor affecting the GPP of phytoplankton, and the effect of nutrients may be negligible in the eutrophic lake on account of temperature limit, which showed that the GPP of algae was only affected by the physical process. In summer and fall, temperature didn't affect the GPP of algae, and the presence of nutrients was the secondary factor affecting the GPP of phytoplankton. From summer to fall, effect of phosphorus was weakened and effect of nitrogen was enhanced.

A shady phytoplankton paradox: when phytoplankton increases under low light.

Light is a fundamental driver of ecosystem dynamics, affecting the rate of photosynthesis and primary production. In spite of its importance, less is known about its community-scale effects on aquatic ecosystems compared with those of nutrient loading. Understanding light limitation is also important for ecosystem management, as human activities have been rapidly altering light availability to aquatic ecosystems. Here we show that decreasing light can paradoxically increase phytoplankton abundance in shallow lakes. Our results, based on field manipulation experiments, field observations and models, suggest that, under competition for light and nutrients between phytoplankton and submersed macrophytes, alternative stable states are possible under high-light supply. In a macrophyte-dominated state, as light decreases phytoplankton density increases, because macrophytes (which effectively compete for nutrients released from the sediment) are more severely affected by light reduction. Our results demonstrate how species interactions with spatial heterogeneity can cause an unexpected outcome in complex ecosystems. An implication of our findings is that partial surface shading for controlling harmful algal bloom may, counterintuitively, increase phytoplankton abundance by decreasing macrophytes. Therefore, to predict how shallow lake ecosystems respond to environmental perturbations, it is essential to consider effects of light on the interactions between pelagic and benthic producers.

Connectivity among Photosystem II centers in phytoplankters: Patterns and responses.

Fast Repetition and Relaxation chlorophyll fluorescence induction is used to estimate the effective absorption cross section of PSII (σPSII), to analyze phytoplankton acclimation and electron transport. The fitting coefficient ρ measures excitation transfer from closed PSII to remaining open PSII upon illumination, which could theoretically generate a progressive increase in σPSII for the remaining open PSII. To investigate how ρ responds to illumination we grew marine phytoplankters with diverse antenna structures (Prochlorococcus, Synechococcus, Ostreococcus and Thalassiosira pseudonana) under limiting or saturating growth light. Initial ρ varied with growth light in Synechococcus and Thalassiosira. With increasing actinic illumination PSII closed progressively and ρ decreased for all four taxa, in a pattern explicable as an exponential decay of ρ with increasing distance between remaining open PSII reaction centers. This light-dependent down-regulation of ρ allows the four phytoplankters to limit the effect of increasing light upon σPSII. The four structurally distinct taxa showed, however, distinct rates of response of ρ to PSII closure, likely reflecting differences in the spacing or orientation among their PSII centers. Following saturating illumination recovery of ρ in darkness coincided directly with PSII re-opening in Prochlorococcus. Even after PSII had re-opened in Synechococcus a transition to State II slowed dark recovery of ρ. In Ostreococcus sustained NPQ slowed dark recovery of ρ. In Thalassiosira dark recovery of ρ was slowed, possibly by a light-induced change in PSII spacing. These patterns of ρ versus PSII closure are thus a convenient probe of comparative PSII spacings.

Diatom growth responses to photoperiod and light are predictable from diel reductant generation.

Light drives phytoplankton productivity, so phytoplankton must exploit variable intensities and durations of light exposure, depending upon season, latitude, and depth. We analyzed the growth, photophysiology and composition of small, Thalassiosira pseudonana, and large, Thalassiosira punctigera, centric diatoms from temperate, coastal marine habitats, responding to a matrix of photoperiods and growth light intensities. T. pseudonana showed fastest growth rates under long photoperiods and low to moderate light intensities, while the larger T. punctigera showed fastest growth rates under short photoperiods and higher light intensities. Photosystem II function and content responded primarily to instantaneous growth light intensities during the photoperiod, while diel carbon fixation and RUBISCO content responded more to photoperiod duration than to instantaneous light intensity. Changing photoperiods caused species-specific changes in the responses of photochemical yield (e- /photon) to growth light intensity. These photophysiological variables showed complex responses to photoperiod and to growth light intensity. Growth rate also showed complex responses to photoperiod and growth light intensity. But these complex responses resolved into a close relation between growth rate and the cumulative daily generation of reductant, across the matrix of photoperiods and light intensities.

Partitioning of the diffuse attenuation coefficient for photosynthetically available irradiance in a deep dendritic tropical lake.

We studied the effects of particulate and dissolved optically active components on the attenuation of photosynthetic active radiation (PAR) in a tropical lake. The temporal and spatial distribution of tripton, Chl-a and aCDOM(440) and their relative contribution to the diffuse PAR attenuation coefficient (Kd) was investigated at 21 sites (dry and wet seasons and two intermediate periods) and at monthly interval at 1 pelagic site. Higher values of ​​ Kd were observed during the mixing period, characterized by a higher concentration of tripton and Chl-a compared to the stratified rainy season. In the spatial sampling PAR attenuation was dominated by tripton absorption/scattering (average relative contribution of 79%), followed by Chl-a (average 11.6%). In the monthly sampling tripton and Chl-a accounted for most of the Kd with relative contributions of 47.8% and 35.6%, respectively. Multiple linear regression analysis showed that Chl-a and tripton in combination explained 97% of the monthly variation in Kd (p<0.001), but Chl-a had more influence (higher regression coefficient). Thus, although most of light attenuation was due to tripton, seasonal variations in phytoplankton abundance were responsible for most of the temporal fluctuations in Kd.

The impact of irradiance on optimal and cellular nitrogen to phosphorus ratios in phytoplankton.

Phytoplankton acclimates to irradiance by regulating the cellular content of light-harvesting complexes, which are nitrogen (N) rich and phosphorus (P) poor. Irradiance is thus hypothesised to influence the cellular N : P ratio and the N : P defining the threshold between N and P limitation (the 'optimal' N : P). We tested this hypothesis by first addressing the response of the optimal N : P to irradiance in a controlled experiment with Chlamydomonas reinhardtii. Then, we did a meta-analysis of experimental data on optimal and cellular N : P ratios across light gradients to test the generality of an N : P to light response within species. In both the experiment and the meta-analysis, N : P ratios decreased with irradiance, indicating that factors affecting underwater irradiance, like depth and the composition of the water, may influence the relative N : P requirement. The effect of irradiance did not differ between optimal and cellular N : P ratios, but observations of optimal N : P were on average 2.8 times higher than observations of cellular N : P.

Assessment of the Effects of Light Availability on Growth and Competition Between Strains of Planktothrix agardhii and Microcystis aeruginosa.

In this study, we tested the hypothesis that Planktothrix agardhii strains isolated from a tropical water body were better competitors for light than Microcystis aeruginosa strains. These cyanobacteria are common in eutrophic systems, where light is one of the main drivers of phytoplankton, and Planktothrix is considered more shade-adapted and Microcystis more high-light tolerant. First, the effect of light intensities on growth was studied in batch cultures. Next, the minimum requirement of light (I*) and the effect of light limitation on the outcome of competition was investigated in chemostats. All strains showed similar growth at 10 µmol photons m(-2) s(-1), demonstrating the ability of the two species to grow in low light. The optimum light intensity was lower for P. agardhii, but at the highest light intensity, Microcystis strains reached higher biovolume, confirming that P. agardhii has higher sensitivity to high light. Nonetheless, P. agardhii grew in light intensities considered high (500 µmol photons m(-2) s(-1)) for this species. M. aeruginosa showed a higher carrying capacity in light-limited condition, but I* was similar between all the strains. Under light competition, Microcystis strains displaced P. agardhii and dominated. In two cases, there was competitive exclusion and in the other two P. agardhii managed to remain in the system with a low biovolume (≈15%). Our findings not only show that strains of P. agardhii can grow under higher light intensities than generally assumed but also that strains of M. aeruginosa are better competitors for light than supposed. These results help to understand the co-occurrence of these species in tropical environments and the dominance of M. aeruginosa even in low-light conditions.

Production of a thermal stress resistant mutant Euglena gracilis strain using Fe-ion beam irradiation.

Euglena gracilis is a common phytoplankton species, which also has motile flagellate characteristics. Recent research and development has enabled the industrial use of E. gracilis and selective breeding of this species is expected to further expand its application. However, the production of E. gracilis nuclear mutants is difficult because of the robustness of its genome. To establish an efficient mutation induction procedure for E. gracilis, we employed Fe-ion beam irradiation in the RIKEN RI beam factory. A decrease in the survival rate was observed with the increase in irradiation dose, and the upper limit used for E. gracilis selective breeding was around 50 Gy. For a practical trial of Fe-ion irradiation, we conducted a screening to isolate high-temperature-tolerant mutants. The screening yielded mutants that proliferated faster than the wild-type strain at 32 °C. Our results demonstrate the effectiveness of heavy-ion irradiation on E. gracilis selective breeding.

A nonlocal and periodic reaction-diffusion-advection model of a single phytoplankton species.

In this article, we are concerned with a nonlocal reaction-diffusion-advection model which describes the evolution of a single phytoplankton species in a eutrophic vertical water column where the species relies solely on light for its metabolism. The new feature of our modeling equation lies in that the incident light intensity and the death rate are assumed to be time periodic with a common period. We first establish a threshold type result on the global dynamics of this model in terms of the basic reproduction number R0. Then we derive various characterizations of R0 with respect to the vertical turbulent diffusion rate, the sinking or buoyant rate and the water column depth, respectively, which in turn give rather precise conditions to determine whether the phytoplankton persist or become extinct. Our theoretical results not only extend the existing ones for the time-independent case, but also reveal new interesting effects of the modeling parameters and the time-periodic heterogeneous environment on persistence and extinction of the phytoplankton species, and thereby suggest important implications for phytoplankton growth control.

Effect of light on the growth of non-nitrogen-fixing and nitrogen-fixing phytoplankton in an aquatic system.

We discuss a mathematical model of growth of two types of phytoplankton, non-nitrogen-fixing and nitrogen-fixing, that both require light in order to grow. We use general functional responses to represent the inhibitory effect their biomass has on the exposure to light. We give conditions for the existence and local stability of all of the possible steady-states (die out, single species survival, and coexistence). We derive conditions for global stability of the die out and single-species steady-states and for persistence of both species when the coexistence steady-state exists. Numerical investigation illustrates the qualitative dynamics demonstrating that even under constant environmental conditions, both stable intrinsic oscillatory behavior and a period doubling route to chaotic dynamics are possible. We also show that competitor-mediated coexistence can occur due to the positive feedback resulting from recycling by the nitrogen-fixing phytoplankton. To show the impact of seasonal change in water depth, we also allow the water depth to vary in an annual cycle and discuss echo blooms in this context.

[Hygienic and environmental problems of energy-saving illumination in urbanization of Crimea].

The article considers the problems offloodlights pollution in the territory of Crimea due to the work of illumination led equipment of the key elements of the international transport artery "China-Europe". There was performed a qualitative assessment of characteristics of led floodlights pollution on the example of the sea surface of the transport crossing through the Kerch Strait. Ichthyologists and oceanographers were shown to estimate the amount of phytoplankton biomass based on sunlight illumination. The excess dose of blue light in the spectrum of led lighting was established to have an impact on phytoplankton greater than solar and lunar light, creating preconditions for the increase of biological mass of phytoplankton and consequently to the formation of the "stern stock". Arising from additional phytoplankton biomass can significantly influence on the schedule offish migration in waters of the Kerch Strait, the biomass of mosquitoes and midges, which are prey for amphibians and birds. The decline of the both light pollution and its negative impact on fauna andflora requires the development of semiconductor sources of white light with a biologically adequate spectrum in the framework of the "Lighting of the lighting equipment of Crimea".

Changes in the Rubisco to photosystem ratio dominates photoacclimation across phytoplankton taxa.

When growth irradiance changes, phytoplankton acclimates by changing allocations to cellular components to re-balance their capacity to absorb photons versus their capacity to use the electrons from the oxidation of water at photosystem II. Published changes in the cellular allocations resulting from photoacclimation across algal groups highlight that algae adopt different strategies. We examined the photoacclimation of the photosynthetic apparatus of six marine phytoplankters under near-natural diel irradiance patterns. For most of the phytoplankters, Chl a per structural photosystem II unit decreased with increasing growth irradiance, but a parallel decline in optical packaging effect allowed cells to maintain their functional absorption cross section serving active photosystem II units (σ PSII). Furthermore, no significant changes were observed in the ratio of Chl a per photosystem I. The diatom Skeletonema marinoi proved an exception to this pattern as Chl a per photosystem II is stable and Chl a per photosystem I slightly decreased with light intensity. A clear decrease in the photosystem content per cell was observed for all species except for Thalassiosira oceanica and S. marinoi. Rubisco content per cell showed little variation with irradiance for most algae, except for a 3-fold increase in S. marinoi. A ~700 % increase in the Rubisco:photosystem ratio across species with increasing growth irradiance indicates this is a key cellular stoichiometric adjustment to balance photon absorption capacity and the carbon reduction capacity. Increasing the Rubisco:photosystem ratio occurs through a decrease in the photosystems per cell for most of the phytoplankters in this study, except in the case of S. marinoi where Rubisco per cell increased.

Climate change enhances primary production in the western Antarctic Peninsula.

Intense regional warming was observed in the western Antarctic Peninsula (WAP) over the last 50 years. Here, we investigate the impact of climate change on primary production (PP) in this highly productive region. This study is based on temporal data series of ozone thickness (1972-2010), sea ice concentration (1978-2010), sea-surface temperature (1990-2010), incident irradiance (1988-2010) and satellite-derived chlorophyll a concentration (Chl-a, 1997-2010) for the coastal WAP. In addition, we apply a photosynthesis/photoinhibition spectral model to satellite-derived data (1997-2010) to compute PP and examine the separate impacts of environmental forcings. Since 1978, sea ice retreat has been occurring earlier in the season (in March in 1978 and in late October during the 2000s) while the ozone hole is present in early spring (i.e. August to November) since the early 1990s, increasing the intensity of ultraviolet-B radiation (UVBR, 280-320 nm). The WAP waters have also warmed over 1990-2010. The modelled PP rates are in the lower range of previously reported PP rates in the WAP. The annual open water PP in the study area increased from 1997 to 2010 (from 0.73 to 1.03 Tg C yr(-1) ) concomitantly with the increase in the production season length. The coincidence between the earlier sea ice retreat and the presence of the ozone hole increased the exposure to incoming radiation (UVBR, UVAR and PAR) and, thus, increased photoinhibition during austral spring (September to November) in the study area (from 0.014 to 0.025 Tg C yr(-1) ). This increase in photoinhibition was minor compared to the overall increase in PP, however. Climate change hence had an overall positive impact on PP in the WAP waters.

The dynamics of temperature and light on the growth of phytoplankton.

Motivated by some lab and field observations of the hump shaped effects of water temperature and light on the growth of phytoplankton, a bottom-up nutrient phytoplankton model, which incorporates the combined effects of temperature and light, is proposed and analyzed to explore the dynamics of phytoplankton bloom. The population growth model reasonably captures such observed dynamics qualitatively. An ecological reproductive index is defined to characterize the growth of the phytoplankton which also allows a comprehensive analysis of the role of temperature and light on the growth and reproductive characteristics of phytoplankton in general. The model provides a framework to study the mechanisms of phytoplankton dynamics in shallow lake and may even be employed to study the controlled phytoplankton bloom.

Simulating the effects of light intensity and carbonate system composition on particulate organic and inorganic carbon production in Emiliania huxleyi.

Coccolithophores play an important role in the marine carbon cycle. Variations in light intensity and external carbonate system composition alter intracellular carbon fluxes and therewith the production rates of particulate organic and inorganic carbon. Aiming to find a mechanistic explanation for the interrelation between dissolved inorganic carbon fluxes and particulate carbon production rates, we develop a numerical cell model for Emiliania huxleyi, one of the most abundant coccolithophore species. The model consists of four cellular compartments, for each of which the carbonate system is resolved dynamically. The compartments are connected to each other and to the external medium via substrate fluxes across the compartment-confining membranes. By means of the model we are able to explain several pattern observed in particulate organic and inorganic carbon production rates for different strains and under different acclimation conditions. Particulate organic and inorganic carbon production rates for instance decrease at very low external CO2 concentrations. Our model suggests that this effect is caused mainly by reduced HCO3(-) uptake rates, not by CO2 limitation. The often observed decrease in particulate inorganic carbon production rates under Ocean Acidification is explained by a downregulation of cellular HCO3(-) uptake.

Light availability may control extracellular phosphatase production in turbid environments.

Extracellular phosphatase production by phytoplankton was investigated in the moderately eutrophic Lipno reservoir, Czech Republic during 2009 and 2010. We hypothesized that production of extracellular phosphatases is an additional mechanism of phosphorus acquisition enabling producers to survive rather than to dominate the phytoplankton. Hence, we examined the relationship between light availability and phosphatase production, as light plays an important role in polymictic environments. Bulk phosphatase activity was measured using a common fluorometric assay, and the production of phosphatases was studied using the Fluorescently Labelled Enzyme Activity technique, which enabled direct microscopic detection of phosphatase-positive cells. In total, 29 taxa of phytoplankton were identified during both years. Only 17 taxa from the total number of 29 showed production of extracellular phosphatases. Species dominating the phytoplankton rarely produced extracellular phosphatases. In contrast, taxa exhibiting phosphatase activity were present in low biomass in the phytoplankton assemblage. Moreover, there was a significant relationship between the proportion of phosphatase positive species in samples and the Z(eu):Z(mix) ratio (a proxy of light availability). A laboratory experiment with different light intensities confirmed the influence of light on production of phosphatases. Our seasonal study confirmed that extracellular phosphatase production is common in low-abundance populations but not in dominant taxa of the phytoplankton. It also suggested the importance of sufficient light conditions for the production of extracellular phosphatases.

Combined Effects from γ Radiation and Fluoranthene Exposure on Carbon Transfer from Phytoplankton to Zooplankton.

Risk assessment does not usually take into account mixtures of contaminants, thus potentially under- or overestimating environmental effects. We investigated how the transfer of carbon between a primary producer, Pseudokirchneriella subcapitata, and a consumer, Daphnia magna, is affected by acute exposure of γ radiation (GR) in combination with the polycyclic aromatic hydrocarbon fluoranthene (FA). We exposed D. magna to five concentrations of FA and five acute doses of GR as single contaminants and in nine binary combinations. We compared the observed data for three end points (incorporation of carbon by D. magna, D. magna ingestion rates, and growth) to the predicted joint effects of the mixed stressors based on the independent action (IA) concept. There were deviations from the IA predictions, especially for ingestion rates and carbon incorporation by D. magna, where antagonistic effects were observed at the lower doses, while synergism was seen at the highest doses. Our results highlight the importance of investigating the effects of exposure to GR in a multistressor context. In mixtures of GR and FA, the IA-predicted effects seem to be conservative as antagonism between the two stressors was the dominant pattern, possibly due to stimulation of cellular antioxidative stress mechanisms.