María Altamirano

Long-Term Effects of Natural Sunlight under Various Ultraviolet Radiation Conditions on Growth and Photosynthesis of Intertidal Ulva rigida (Chlorophyceae) Cultivated In Situ

Abstract Long-term effects of full-spectrum solar radiation, solar radiation without UVB, and solar radiation without total UV (UVA + UVB) radiation were studied in intertidal Ulva rigida C. Agardh (Chlorophyta). The experiment was carried out under natural conditions and at prevailing winter levels of UV radiation. Changes in relative growth rate, photosynthesis and pigment content were studied after 7 and 20 d of cultivation under the three solar radiation conditions. Relative growth rate was enhanced (50 %) in the absence of UVB radiation after one week, but no difference was found after 20 d. Pigment content (chlorophyll a, chlorophyll b and carotenoids) was significantly higher in the presence of UVB, suggesting an efficient protective-pigment mechanism. When UVB was removed, photosynthetic performance measured as oxygen exchange and fluorescence parameters exhibited higher values than under the other treatments after 7 d of incubation. When samples were cultivated under PAR alone, photosynthetic performance was always negatively affected compared to in the presence of UV radiation. On the whole, intertidal U. rigida exhibited a remarkable capacity to cope with fluctuating light conditions.

Involvement of solar UV-B radiation in recovery of inhibited photosynthesis in the brown alga Dictyota dichotoma (Hudson) Lamouroux

Daily variations of photosynthetic performance of the brown alga Dictyota dichotoma (Hudson) Lamouroux (Dictyotales) (estimated by Fv/Fm ratio and net O2-based photosynthesis) have been determined under full-spectrum solar radiation (PAR+UV-A+UV-B), solar radiation depleted of ultraviolet-B (PAR+UV-A) and solar radiation depleted of total ultraviolet (photosynthetically active radiation, PAR). In the daily course, the photosynthetic response of the alga is inhibited by the three solar radiation conditions at midday, but recovers during the afternoon to those values measured in the early morning only under PAR + UV-A + UV-B, or PAR alone. Under solar radiation depleted of UV-B, the recovery of photosynthesis is significantly lower than in the other two solar radiation conditions. The relative electron transport rate (ETR) as a function of PAR is calculated for the three radiation treatments, at noon after 2 h exposure. The ETR is strongly inhibited under these conditions. In the PAR and PAR + UV-A + UV-B treatments, photosynthesis recovers after 1.5 h in low irradiance (< 10 μmol photons m−2 s−1) and attains values measured in the early morning. In the absence of UV-B, the inhibitory effect is persistent, visible as a low initial slope and lower ETR at higher levels of irradiance. These data suggest that UV-B may be involved both in the impairment and the recovery of photosynthesis of D. dichotoma.

Effects of UV radiation and temperature on growth of germlings of three species of Fucus (Phaeophyceae)

Measurements of relative growth rates (RGR) of germlings of three species of Fucus (Fucales, Phaeophyceae) collected in Helgoland (North Sea, Germany) were carried out in the laboratory in order to determine the effects of different ultraviolet radiation (UVR, λ = 280–400 nm) conditions, UVR doses and temperatures. High ultraviolet-B radiation (UVBR, λ = 280–315 nm) levels and low temperature, as independent factors, led to a species-specific reduction in RGR which appears to be related to the vertical distribution of the species in the intertidal zone. The inhibition of RGR ranged from 10% to even death of the germling. For the most sensitive species, high temperature in combination with a high dose of UVBR caused the death of the germlings, whereas at low temperature germlings were able to survive. This suggest growth-related temperature dependence of sensitivity to UVBR.

Growth seasonality, photosynthetic pigments, and carbon and nitrogen content in relation to environmental factors: a field study of Ulva olivascens (Ulvales, Chlorophyta)

Abstract Relative growth rate, photosynthetic pigment content, and internal carbon and nitrogen levels of Ulva olivascens P.A. Dangeard, were examined on a seasonal basis under natural conditions from December 1994 to February 1996. Biotic variables were correlated with abiotic factors, including phosphate and nitrate/nitrite [(NO3− + NO2−)] concentrations in the seawater, temperature, photosynthetically active radiation (PAR), and UV-A and UV-B radiation. The relative growth rate of the alga was 68% higher in spring and early summer than in mid summer. In the same spring-to-summer period, photosynthetic pigment concentrations (chlorophyll a, chlorophyll b, and carotenoids) decreased by 70–80%. From March to July, nitrogen and carbon content declined by 62% and 11%, respectively, which yielded a change in the carbon: nitrogen mass ratio from 12.9 to 39.4. In late summer, the alga disappeared from the field site. Seasonal variations in relative growth rate of U. olivascens were governed by changes in primary ecological factors, i.e., [NO3− + NO2−] concentration (70%), PAR (15%), UV-B (5%), and temperature (4%). UV-B and UV-A radiations and PAR, were primarily responsible for the seasonal changes in chlorophyll a and b and carotenoid contents. More than 78% of the changes in internal carbon and nitrogen levels could be explained by seasonal changes in UV-B radiation. These results suggest that the metabolic stress due to UV-B radiation has little impact on the seasonal growth cycle of U. olivascens but has significant impact on pigments and internal carbon and nitrogen content.

Photosynthetic performance and pigment content in the aquatic liverwort Riella helicophylla under natural solar irradiance and solar irradiance without ultraviolet light

Abstract The effects of solar radiation and solar radiation deprived of ultraviolet radiation (λ

Analysis of polygenic traits of Microcystis aeruginosa (Cyanobacteria) strains by Restricted Maximum Likelihood (REML) procedures: 1. Size and shape of colonies and cells

M. Rico, M. Altamirano, V. López-Rodas and E. Costas. 2006. Analysis of polygenic traits of Microcystis aeruginosa (Cyanobacteria) strains by Restricted Maximum Likelihood (REML) procedures: 1. Size and shape of colonies and cells. Phycologia 45: 237–242. DOI: 10.2216/03-44.1 Traditionally, morphometrical traits are used to classify cyanobacteria. However, neither the importance of genetic factors in morphological variability nor genetic correlations between different morphometrical traits are known. Six morphometrical traits of individual cells and six morphometrical traits of colonies have been measured in 21 strains of Microcystis aeruginosa. A fixed model and a mixed model allowing genetic relationships between traits were both used to estimate genetic and residual correlations, and genetic variance/total phenotypic variance ratios were used to estimate the 12 morphometrical traits. Results showed that (1) colony size has a low genetic correlation with traits of individual cells; (2) traits measured on individual cells present a higher genetic variance/total phenotypic variance ratio than the corresponding trait in colonies; and (3) genetic correlations between directly measured traits (maximal diameter and axis, minimal diameter and axis, perimeter, and surface) are so high that they may be considered different expressions of the same underlying trait, namely size, so any one of them could be used without significant loss of information, instead of all of them. Fixed and mixed models showed the same conclusions, although mixed models preferably should be used because they take into account the common random genetic basis of traits. Maximal cell diameter was used as a discriminator trait for studying morphological differences between strains from different origins. Results suggest that environment may modulate strain mixtures in Microcystis populations.

Analysis of polygenic traits of Microcystis aeruginosa (Cyanobacteria) strains by Restricted Maximum Likelihood (REML) procedures: 2. Microcystin net production, photosynthesis and respiration

V. López-Rodas, E. Costas, E. Bañares, L. García-Villada, M. Altamirano, M. Rico, C. Salgado and A. Flores-Moya. 2006. Analysis of polygenic traits of Microcystis aeruginosa (Cyanobacteria) strains by restricted maximum likelihood (REML) procedures: 2. Microcystin net production, photosynthesis and respiration. Phycologia Phycologia 45: 243–248. DOI: 10.2216/04-31.1 Phenotypic expression of traits is the result of complex interactions between genotype and environment. A combination of experiments and statistics based on restricted maximum likelihood (REML) procedures was utilised for estimating the proportion of genetic variability in a series of phenotypic characters (microcystin net production, cell size, dark respiration rate, photosynthetic capacity, maximum quantum yield and growth rate), as well as their genetic and nongenetic correlations, measured on 18 Microcystis aeruginosa (Cyanobacteria) strains. Results indicated that the phenotypic variability found in these traits were principally due to genetic differences among strains. Thus, the estimated genetic variability ranged from ≈ 50% for dark respiration rate to > 90% in cell size or maximum quantum yield. These results support the conclusions that (1) genetic factors are the main cause of the spatial-temporal heterogeneity observed in quantum yield, respiration and toxin production, and (2) light harvesting and toxin production are not under intense natural selection, both having a low adaptive value. The high variance in toxin production resulting from genetic effects introduces a source of unpredictability in water-supply toxic early warnings. In addition, no significant genetic correlations were found between quantum yield and either maximal growth rate or mean cell diameter.

Morphological differentiation of cryptic lineages within the invasive genus Asparagopsis (Bonnemaisoniales, Rhodophyta)

Abstract: Rapid identification of introduced seaweeds is crucial to support management and conservation decisions, especially when multiple cryptic lineages of high-profile invasive taxa occur sympatrically. The red seaweed genus Asparagopsis (Bonnemaisoniales, Rhodophyta) comprises two recognised morpho-species characterised by heteromorphic life cycles and presumably morphologically identical ‘Falkenbergia’ tetrasporophyte stages: A. armata and A. taxiformis. Populations of the former were easily identified by the presence of distinctive harpoon-like braches on the gametophyte thalli. Four morphologically cryptic yet genetically distinct mitochondrial lineages of invasive nature were recognised within A. taxiformis. We reported a morphological delineation of tetrasporophytes and gametophytes of Asparagopsis, including cryptic lineages collected from the Mediterranean Sea and the Hawaiian Islands, where multiple Asparagopsis lineages were present. Vegetative anatomical characters of the tetrasporophytes were useful in differentiating A. armata from those of A. taxiformis as well as among tetrasporophyte isolates belonging to the four A. taxiformis lineages. In addition, these characters distinguished lineage 2 native range specimens (Hawaii) from the invasive specimens (Mediterranean Sea), which suggested high levels of morphological plasticity in the invasive taxon. We propose that the taxonomic status of the lineages within A. taxiformis needs to be revised.

Photosynthetic performance of phototrophic biofilms in extreme acidic environments

Photosynthesis versus irradiance curves and their associated photosynthetic parameters from different phototrophic biofilms isolated from an extreme acidic environment (Río Tinto, SW, Spain) were studied in order to relate them to their species composition and the physicochemical characteristics of their respective sampling locations. The results indicated that the biofilms are low light acclimated showing a photoinhibition model; only floating communities of filamentous algae showed a light saturation model. Thus, all the biofilms analysed showed photoinhibition over 60 µmol photon m(-2) s(-1) except in the case of Zygnemopsis sp. sample, which showed a light-saturated photosynthesis model under irradiations higher that 200 µmol photon m(-2) s(-1). The highest values of compensation light intensity (I(c)) were showed also by Zygnemosis sp. biofilm (c. 40 µmol photon m(-2) s(-1)), followed by Euglena mutabilis and Chlorella sp. samples (c. 20 µmol photon m(-2) s(-1)). The diatom sample showed the lowest I(c) values (c. 5 µmol photon m(-2) s(-1)). As far as we know this is the first attempt to determine the photosynthetic activity of low pH and heavy metal tolerant phototrophic biofilms, which may give light in the understanding of the ecological importance of these biofilms for the maintenance of the primary production of these extreme and unique ecosystems.

Stage-dependent sensitivity to ultraviolet radiation in zygotes of the brown alga Fucus serratus.

Sensitivity to ultraviolet (UV) radiation (UV-A, lambda = 315-400 nm; plus UV-B, lambda = 280-315 nm) of zygotes of the brown alga Fucus serratus L. (Phaeophyta) has been assessed through effects on growth of developing germlings. Different stages of development were distinguished by considering 5 h periods of time after fertilisation. Both the stage of the zygote and the UV radiation condition significantly affected growth of developing germlings. The negative response of growth rate of early stages of the zygotes to UV radiation seemed to be caused by UV-B rather than UV-A radiation, as the lowest relative growth rates were always estimated for germlings developed from zygotes irradiated with UV-B radiation. As regards the stage of the zygote, those germlings that developed from zygotes irradiated at 5-10 h after fertilisation showed the strongest inhibition of growth compared with the other stages. These results point to polarisation as the most UV-sensitive process during the first 24 h of the development of the zygote. A non-linear relationship between the developmental stage of the zygote and the sensitivity to UV radiation is suggested.