Algal Layer Research Articles

Активность супероксиддисмутазы и каталазы в лишайниках с разным составом фотобионтов

Data on the activity of catalase and superoxide dismutase in the thalli of the cyanolichen Peltigera praetextata and the green algal lichen Hypogymnia physodes (See Fig. 1) at different ontogenetic conditions are not available in the literature. At the same time, the study of antioxidant system of lichen thalli with different photobionts during ontogenesis is relevant and can contribute to understanding the mechanisms of adaptation of symbionts to changing environmental conditions, and also serve as indicators of the functional state of the organism. The aim of the study was to investigate the activity of catalase and superoxide dismutase enzymes in lichen thalli P. praetextata and H. physodes at different stages of ontogenesis. P. praetextata and H. physodes thalli samples were collected from aspen and pine trunks under similar ecological conditions of mixed aspen-spruce communities in the middle taiga (62°15'15.9'' N, 33°58'746.1'' E, 61°50'17'' N, 34°23'13'' E, the Republic of Karelia) and northern taiga (64°34'13.9' 'N, 43°15'48'' E, Arkhangelsk Oblast, 64° 33'19'' N, 30°20'46'' E, the Republic of Karelia). Based on morphological features, thalli samples were divided into groups of different age. P. praetextata thalli were divided into 3 groups: virginal (pregenerative, young thalli without reproduction structures), generative (thalli with apothecia and phyllidia – structures of vegetative reproduction), and senile thalli (thalli with signs of degradation over a larger area). H. physodes thalli were divided into 2 groups: virginil and senile thalli; generative thalli with apothecia are extremely rare in the study areas. Catalase activity measured based on enzymatic degradation of hydrogen peroxide, superoxide dismutase activity was determined spectrophotometrically by inhibition of photoreduction of nitroblue tetrazolium, protein content was determined by the method Bradford. Statistical analysis of the data was carried out using one-way analysis of variance. The protein content (mg/g dry mass) in P. praetextata thalli within the studied sample averaged 1.12 ± 0.09, in H. physodes thalli – 2.45 ± 0.32. The activity of superoxide dismutase (units/mg of protein) in thalli of P. praetextata reached an average of 0.34 ± 0.12, in thalli of H. physodes – 0.09 ± 0.01. The values of catalase activity (µmol H2O2/µg protein) in P. praetextata thalli averaged 2.06 ± 0.48, H. physodes – 0.49 ± 0.07. For the thalli of the cyanolichen P. praetextata, a lower (2 times) protein content (See Fig. 2) and a higher (4-5 times) activity of superoxide dismutase (See Fig. 3) and catalase (See Fig. 4) were found in compared with the chlorobiont lichen H. physodes. The species P. praetextata belongs to the group of cyanolichens, and its photobiont is cyanobacteria of the genus Nostoc located in the algal layer of the thallus. In both lichen species, the maximum values of catalase activity were established for virginal thalli, and the minimum values for senile thalli. Perhaps this is due to the high intensity of "growth respiration" of young lichen thalli, which leads to the formation of reactive oxygen species. Differences in the activity of superoxide dismutase in thalli of different ontogenetic stages in the studied species were not shown. In the thalli of P. praetextata and H. physodes, the activity of catalase in thalli from the northern taiga communities is higher than in the thalli of the middle taiga, while the activity of superoxide dismutase, on the contrary, was on average higher in the lichen thalli of the middle taiga. This might be due to variability in the intensity of photosynthesis and respiration along the latitudinal gradient. In lichens, catalase activity can be a marker of mycobiont respiration, and superoxide dismutase activity is a marker of photobiont photosynthesis. The question of contribution of the fungal or algal components of the lichen thallus to the activity of antioxidant enzymes remains open.

Regulation of symbiotic interactions and primitive lichen differentiation by UMP1 MAP kinase in Umbilicaria muhlenbergii

AbstractLichens are of great ecological importance but mechanisms regulating lichen symbiosis are not clear. Umbilicaria muhlenbergii is a lichen-forming fungus amenable to molecular manipulations and dimorphic. Here, we established conditions conducive to symbiotic interactions and lichen differentiation and showed the importance of UMP1 MAP kinase in lichen development. In the initial biofilm-like symbiotic complexes, algal cells were interwoven with pseudohyphae covered with extracellular matrix. After longer incubation, fungal-algal complexes further differentiated into primitive lichen thalli with a melanized cortex-like and pseudoparenchyma-like tissues containing photoactive algal cells. Mutants deleted of UMP1 were blocked in pseudohyphal growth and development of biofilm-like complexes and primitive lichens. Invasion of dividing mother cells that contributes to algal layer organization in lichens was not observed in the ump1 mutant. Overall, these results showed regulatory roles of UMP1 in symbiotic interactions and lichen development and suitability of U. muhlenbergii as a model for studying lichen symbiosis.

Do urban air pollutants induce changes in the thallus anatomy and affect the photosynthetic efficiency of the nitrophilous lichen Physcia adscendens?

Lichens are symbiotic organisms that are generally sensitive to air pollution due to their specific biological and physiological features. Physcia adscendens is a nitrophilous lichen well-known for being resistant to air pollution associated with progressive anthropopressure. The aim of this study was to investigate the effect of nitrogen oxides and suspended particulate matter (PM10 and PM2.5) on anatomical structure of the thallus and photobiont’s photosynthetic efficiency in P. adscendens inhabiting sites that differ in terms of air pollution level and thereby to determine the relevance of these pollutants for shaping the structure of the thallus and the physiological condition of the photosynthetic partner. We found that P. adscendens from polluted sites had increased thickness of the algal layer and the larger size of the algae cells, but a much lower ratio of the algal layer to the whole thallus. Lichens from highly polluted sites had also higher photosynthetic efficiency, which indicates a relatively good physiological condition of the photobiont. This indicates that the photobiont of P. adscendens is well-adapted to function under air pollution stress which may contribute to its success in colonizing polluted sites. Both changes in the anatomy of the lichen thallus and the efficiency of photosynthesis may be related to the enrichment of the environment with nitrogen. The increased photosynthetic efficiency as well as investment in the size of photobiont cells and growth mycobiont hyphae confirms that P. adscendens is well-adapted to urban conditions; however, the mechanism behind those adaptations needs more focus in the context of global environmental changes.

Independent, structurally distinct transitions to microfruticose growth in the crustose genus Porina (Ostropales, Lecanoromycetes): new isidioid species from south-western Florida

AbstractPorina is a widely distributed, species-rich genus of crustose, lichen-forming fungi, some with thalline outgrowths that have been recognized as isidia. We studied three taxa with thalli consisting chiefly of ascending isidioid structures occurring on trunks and branches of Taxodium in southwestern Florida, and provide details of their structure with light and electron microscopy. Two of these taxa we describe as new species: P. microcoralloides and P. nanoarbuscula. Genetic sequences (mtSSU) suggest that they are closely related to each other, yet they differ markedly in the size, morphology and anatomical organization of their isidioid branches as well as in the length of their ascospores. In the three Floridian taxa studied, the crustose portion of the thallus is partly endophloeodic and partly superficial, the latter often patchy, evanescent or inconspicuous, and completely lacks the differentiated anatomical organization characteristic of the isidioid structures arising from it. In Porina microcoralloides, the ascendant thallus consists of branched, coralloid inflated structures with phycobiont (Trentepohlia) unicells arranged at the periphery of a loose central medulla. Sparse fungal cells are interspersed and overlie the algal layer in places, but no differentiated cortex is present, leaving phycobiont cells more or less exposed at the surface. In the closely related Porina nanoarbuscula, the isidioid structures are much finer, more densely branched, and composed of a single, central file of roughly spherical Trentepohlia cells surrounded by a jacket of subglobose fungal cells. The ascospores of P. microcoralloides are more than twice the length of those of P. nanoarbuscula. Although thalli of these two Porina species occur in the same habitats and are sometimes found growing alongside each other, phylogenetic analysis of rbcL sequences suggest that they partner with distinct clades of Trentepohlia phycobionts. A third taxon examined, Porina cf. scabrida, is morphologically rather similar to P. microcoralloides, but the ascendant branches are bright yellow-orange, more cylindrical, and corticated by a thin layer of agglutinated fungal hyphae; perithecia were not seen. Analysis of mtSSU sequences places it distant from P. microcoralloides and P. nanoarbuscula phylogenetically. None of the Floridian taxa studied was particularly close to the European isidiate species Porina hibernica and P. pseudohibernica, which appeared as sister to each other in the analysis. While a particular type of isidiose structure may be reliably characteristic of specific taxa, similarities or differences in these structures do not seem to be useful indicators of phylogenetic proximity or distances among taxa. The morphological trends evident in Porina suggest that multiple transitions from crustose to isidioid or microfruticose growth have arisen repeatedly and in quite different ways within this single genus. At least some of the diverse structures treated within the broad concept of isidia may be representative of the developmental pathways by which fruticose growth forms may arise.

Algal diversity on the granite monument in front of the Faculty of Biology of Sofia University

The paper presents the results on the species composition of aeroterrestrial algae that developed on a granite monument in the urban environment in the central part of the Bulgarian capital town Sofia, situated in front of the Faculty of Biology of Sofia University “St. Kliment Ohridski”. After scraping the visible algal layers from both frontal (northern) and back (southern) side of the monument, samples were immediately processed by conventional light microscopy on non-permanent slides. The algal diversity comprised six species from the following four taxonomic phyla: Cyanoprokaryota, Chlorophyta, Streptophyta and Ochrophyta. The obtained samples are deposited in the Living Algal Collection of Sofia University (ACUS) for further proceeding and cultivation.

The Sub-Ice Algal Communities of the Barents Sea Pack Ice: Temporal and Spatial Distribution of Biomass and Species

This work summarizes ice algal studies, presented as biomass and species temporal and spatial distribution, during 11 cruises conducted between 1986 and 2012. The majority of the biomass was found as loosely attached sub-ice algal layers, and sampling required diving. A maximum of 40 mg chlorophyll m−2 and 15.4 × 109 cells m−2 was measured in May. The species diversity was separated in zones based on ice thickness, with the highest biodiversity in the medium-thick ice of 30–80 cm. Nitzschia frigida was the most common species. There was a significant positive relationship between the dominance of this species and ice thickness, and it dominated completely in thick ice. Other common species, such as N. promare and Fossulaphycus arcticus reacted oppositely, by becoming less dominant in thick ice, but the positive correlation between total cell numbers and number of these three species indicated that they would most likely dominate in most populations. Melosira arctica was found several times below medium-thick annual ice. Algae occurred from top to bottom in the ice floes and in infiltration layers, but in very low numbers inside the ice. The bipolar dinoflagellates Polarella glacialis inhabited the ice, both as vegetative cells and cysts. The algal layers detached from the ice and sank in late spring when melting started. The cells in the sediments form an important food source for benthic animals throughout the year. Fjord populations survive the winter on the bottom and probably form next year’s ice algal inoculum. A few ‘over-summer’ populations found in sheltered locations might provide supplementary food for ice amphipods in late summer. The future faith of the ice flora is discussed in view of a warmer climate, with increased melting of the Arctic ice cover.

Анатомо-морфологические и физиологические особенности талломов цианолишайника Peltigera praetextata (Florke ex Sommerf.) Zopf разных онтогенетических состояний

The goal of this study is to describe the cyanolichen Peltigera praetextata ontogenesis stages and reveal some of their morphological, anatomical, and physiological features. This paper analyzes 300 P. praetextata thalli taken in 2019 from aspen trunks in the aspen-spruce communities of the middle taiga territory in Kivach Nature Reserve (62°15'15.9'N, 33°58'746.1"E) from permanent sample plots. The authors determined the ontogenetic state of each thallus based on morphology and anatomy data using the concept of a discrete approach to the description of ontogenesis (Suetina, 2001). They registered the following thalli parameters: length, width, presence and length of rhizines, presence and width of veins, presence of phyllidia and apothecia, number of notches and lobes, shape, edge curl, and surface tomentum. They studied the anatomical parameters (thallus total thickness, tomentum thickness, cortical layer, algal layer and medulla thickness, algae cell size) using sections of thalli samples in all ontogenetic states from the apical, medial, and basal parts in triplicate. They measured the content of photosynthetic pigments spectrophotometrically with preparation of alcoholic extracts. To assess the parameters of the water regime of thalli having different ontogenetic states, the authors calculated a specific thallus mass (STM) and water holding capacity (WHC). They made a statistical data measurement using one-way ANOVA and regression analysis. They also calculated the coefficient of variation (CV) to assess the variability of the features under study. The study identified four periods and 12 ontogenetic states of P. praetextata: latent (sp), pre-generative (pr, prt, j, iml, im2, im3, vl, v2), generative (g), and post-generative (ss, s). The values of the morphological and anatomical parameters of the thalli increase during their development. The early ontogenesis stages demonstrate the highest variability of the parameters. The highest variability of the thallus structures under study within the ontogenetic states is registered for the rhizine length, vein width, and medulla thickness, while the highest constancy is typical of the share of the algal layer in the thallus that varies within a very limited range (22-32%) and reaches the minimum values in the post-generative period. The mycobiont increases in volume through a medulla growth. The physiological characteristics of the P. praetextata thalli differ in various ontogenetic states, while the generative thalli characterized by a normal ratio of photosynthetic pigments, maximum water saturation, and maximum water holding capacity have the maximum values. Thus, at early development stages, the thalli demonstrate a lower ability to retain moisture and may represent a critical stage in a lichen life cycle. On the one hand, the revealed wide variability of the morphological and anatomical parameters of young thalli testifies to their high adaptability, but the physiological parameters of water saturation indicate the vulnerability of these stages. These parameters confirm the validity of the ontogenetic stages identified. The paper contains 5 Figures, 5 Tables and 55 References. The Authors declare no conflict of interest.

Airborne ascospore discharge with co-dispersal of attached epihymenial algae in some foliicolous lichens.

PremiseLichen‐forming fungi that colonize leaf surfaces must find a compatible algal symbiont, establish lichen symbiosis, and reproduce within the limited life span of their substratum. Many produce specialized asexual propagules that appear to be dispersed by rain and runoff currents, but less is known about dispersal of their meiotic ascospores. In some taxa, a layer of algal symbionts covers the hymenial surface of the apothecia, where asci discharge their ascospores. We examined the untested hypothesis that their ascospores are ejected into air currents and carry with them algal symbionts from the epihymenial layer for subsequent lichenization.MethodsLeaves bearing the lichens Calopadia puiggarii, Sporopodium marginatum (Pilocarpaceae), and Gyalectidium viride (Gomphillaceae) were collected in southern Florida. The latter two species have epihymenial algal layers. Leaf fragments with apotheciate thalli were affixed in petri dishes, with glass cover slips attached inside the lid over the thalli. Subsequent discharge of ascospores and any co‐dispersed algae was evaluated with light microscopy.ResultsAll three species discharged ascospores aerially. Discharged ascospores were frequently surrounded by a halo‐like sheath of transparent material. In the two species with an epihymenial algal layer, most dispersing ascospores (>90%) co‐transported algal cells attached to the spore sheath or wall.ConclusionsWhile water may be the usual vector for their asexual propagules, foliicolous lichen‐forming fungi make use of air currents to disperse their ascospores. The epihymenial algal layer represents an adaptation for efficient co‐dispersal of the algal symbiont with the next genetic generation of the fungus.

Aspiciliella pakistanica a new lichen species (Megasporaceae, Pertusariales, Ascomycota) from Pakistan

A new species in Megasporaceae, Aspiciliella pakistanica is described and illustrated from Pakistan. A comparative morpho–anatomical study and ITS–based molecular analysis confirmed its position within the recently resurrected genus Aspiciliella. The taxon is characterized by whitish–grey thalli having large and thick areoles without pale lines on the surface, and a discontinuous algal layer arranged in groups of vertical rows. Its positioning in a separate branch in the phylogenetic tree also makes it distinct from the other known species of the genus.

Lichen 4. The Algal Layer

A lichen is a slow-growing niche-constructing organism that forms a thallus via scripted symbiotic/mutualist relationships between fungi, algae, and bacteria. Here we use quick-freeze deep-etch electron microscopy (QFDEEM) and light microscopy to probe a hallmark lichen construction wherein clusters of algae and hyphae, inter-connected by wall-to-wall junctions, form stable consortia that we call green modules. These assemble in the pseudo-meristem and then localize to the algal layer of the thallus. In the foliose lobes of Candelaria concolor, the cells in each module are enveloped in a continuous 10-nm-thick film of hydrophobin proteins, which binds to wall and matrix surfaces on its hydrophilic side and faces air or water on its hydrophobic side. We document patterned relationships between modules and associated cords of hyphae destined for the outer layers, and propose ways that these relationships could form the structural foundation for water and air regulation within foliose lobes.

Lichen 3. Outer layers

A lichen is a slow-growing niche-constructing organism that forms a thallus via scripted symbiotic/mutualist relationships between fungi, algae, and bacteria. Here we use quick-freeze deep-etch electron microscopy (QFDEEM), in conjunction with light microscopy, to document the structural manifestations of hyphal differentiation during the formation of three lichen tissues that localize between the algal layer and the surface of the thallus: the outer cortex of foliose lobes; the outer layer of fruticose stems; and the enwrapping layer of asexual propagules called soredia that protrude from squamulose podetia and foliose lobes. Our observations document features of outer-layer architecture and the role played by extracellular matrices (ECM). They also lead us to propose the medullary stem-cell hypothesis for lichen organization wherein totipotent medullary hyphae produce lateral branches that undergo specific differentiation pathways in specific domains of the thallus.

The new genus Pulvinora (Lecanoraceae) for species of the ‘Lecanora pringlei’ group, including the new species Pulvinora stereothallina

Phylogenetic reconstructions based on ITS/5.8S, mtSSU and nuLSU DNA sequence data suggest that Lecanora pringlei from North America and a closely related new species from the Altai Mountains, Russia, should be transferred to a new genus Pulvinora, phylogenetically related to Frutidella. It is distinguished by Lecanora-type asci, mycolecanorine apothecia soon becoming convex with an algal layer pushed below the hypothecium, and a pulvinate thallus with squamules at the tip of pseudopodetia-like, branched, pale brownish structures. Lecanora subcavicola and L. pringlei subsp. brandegeei do not belong to this new genus Pulvinora; consequently, we propose the new combination L. brandegeei to accommodate the latter taxon. Pulvinora stereothallina is distinguished from P. pringlei in the shape and size of its squamules (plane to concave, up to 3.0 mm long vs. remaining convex, up to 1.5 mm long), by the lack of maculae, the presence of a whitish pruina on the margins and elevated parts of its squamules, by apothecia coalescing into clusters (vs. single), an ochre-yellow to brownish (vs. colorless) proper exciple, larger ascospores, and different secondary metabolites. Lectotypes of Lecidea pringlei Tuck. and L. brandegeei Tuck. are designated here from the collections deposited in fh.

Responses of thallus anatomy and chlorophyll fluorescence-based photosynthetic characteristics of two Antarctic species of genus Usnea to low temperature

Biometrical parameters of two fruticose lichens from Antarctica (Usnea aurantiaco-atra, U. sphacelata) were studied using thallus cross-sections at basal, middle, and apical parts of thallus. The thallus diameter (TD), the thickness of the upper cortex (UCT), distribution of symbiotic alga (Trebouxia sp.) in the algal layer, the thickness of medulla (MT), central cord diameter, and area (CCD, CCA) were measured. U. sphacelata had comparable relative UCT (0.080-0.110, relative to diameter) to U. aurantiaco-atra (0.085-0.130). The relative MT was higher in U. sphacelata (0.240-0.300) than U. aurantiaco-atra (0.080-0.180). In U. aurantiaco-atra, the CCA was two times larger than that in U. sphacelata. Rapid freezing of thalli in liquid nitrogen led to an increase in TD, UCT, CCD because of intrathalline ice crystals formation. Cultivation of symbiotic alga at different temperatures (1.5, 6.0, 15.0, 22.0, and 28.0°C) with repetitive chlorophyll fluorescence parameters measurements showed growth optimum of 15.0°C for potential and effective quantum yield.

Heavy-metal pollution induces changes in the genetic composition and anatomical properties of photobionts in pioneer lichens colonising post-industrial habitats

Certain lichens are effective colonisers of polluted sites. However, little is known about the tolerance of photobionts and the degree of mycobiont selectivity to photobionts relative to metal pollution. The present study recognises the genetic and anatomical diversity of Asterochloris photobionts in epigeic lichens, i.e. Cladonia cariosa, C. rei, and Diploschistes muscorum, in relation to a wide spectrum of soil pollution. In accordance with phylogenetic analysis, photobionts were clustered in 7 moderately- to well-supported clades, including 19 haplotypes. The mycobionts of all studied lichens demonstrated a low level of selectivity and were capable of associating with various Asterochloris lineages. This tendency was also expressed by the frequent (~25%) occurrence of multiple algal genotypes in a single thallus. This indicates that identified Asterochloris lineages are generally tolerant to heavy-metal pollution, and the low level of selectivity of mycobionts enables them to select the most suitable and/or available partner. The trend of increasing incidence of certain Asterochloris lineages and decreasing frequency of others along with increasing soil pollution was observed. This proves the superior adaptation of some photobionts to polluted sites. Such symbiotic plasticity constitute an adaptive feature necessary for the successful colonisation. High number of haplotypes at polluted sites could be the result of multiple introduction events from different areas during the initial stages of spontaneous succession. Regardless of the genetic pattern, Asterochloris cells were considerably smaller, and the density and compaction of cells in the algal layer were higher, in lichen specimens from polluted sites, indicating that photobiont characteristics may be closely dependent on heavy-metal pollution.

Stokes drift in coral reefs with depth-varying permeability.

In his famous paper of 1847 (Stokes GG. 1847 On the theory of oscillatory waves. Trans. Camb. Phil. Soc. 8, 441-455), Stokes introduced the drift effect of particles in a fluid that is undergoing wave motion. This effect, now known as Stokes drift, is the result of differences between the Lagrangian and Eulerian velocities of the fluid element and has been well-studied, both in the laboratory and as a mechanism of mass transport in the oceans. On a smaller scale, it is of vital importance to the hydrodynamics of coral reefs to understand drift effects arising from waves on the ocean surface, transporting nutrients and oxygen to the complex ecosystems within. A new model is proposed for a class of coral reefs in shallow seas, which have a permeable layer of depth-varying permeability. We then note that the behaviour of the waves above the reef is only affected by the permeability at the top of the porous layer, and not its properties within, which only affect flow inside the porous layer. This model is then used to describe two situations found in coral reefs; namely, algal layers overlying the reef itself and reef layers whose permeability decreases with depth. This article is part of the theme issue 'Stokes at 200 (part 2)'.

Cortical Windows in Stereocaulon

Green algal photosynthetic units in the genus Stereocaulon (phyllocladia or areoles) are typically white to pale gray, but certain species develop a darker central portion. Structurally, these dark-centered areoles of crustose Stereocaulon are identical to the phyllocladia of the S. vesuvianum group. The dark-centered photosynthetic units may have an adaptive role, separating tissue for gas exchange from tissue for water uptake and light transmission. I hypothesize that the white portions of cortex on the photosynthetic units have reflective extracellular deposits that optically occlude the cortex but allow gas exchange through hydrophobic air channels. In contrast, the dark centers apparently provide transparent and water-transmissive windows into the algal layer through an otherwise relatively opaque cortex. Cortical windows are apparently unusual in lichens and may be an adaptation to provide gas exchange in cold, wet environments. For crustose species, the areoles often protrude from a thin film of water over rock and the dual cortex appears to provide both light transmission and gas exchange. Similarly, for the S. vesuvianum group, the dual cortex may provide light transmission and gas exchange for water-saturated thalli in oceanic environments.

The attached microorganisms on the sand grain surfaces at the Slow Sand Filters

This study was carried out in order to investigate mainly the populations of different microorganisms attached to the sand grain surfaces in the slow sand filter beds at Ashford Common Water-treatment works in London area, U.K. using the mechanical shaking technique. It was proved that this technique is one of the more suitable and safe means in extracting microorganisms attached to particles such as sand grains and/or clay particles by applying the scanning electron microscope technique. The scanning micrographs illustrate that there is a direct proportional declination for the numerical densities of the microorganisms at different depths and various time intervals of shaking, while illumination intensities showed a conspicuous pattern particularly in case of complete shading. Simultaneously, It was too difficult to have any other organisms particularly protozoa in the same micrographs which might be referred to the exaggerated abundance of the algal layer Schmutsdecke, the presence of certain predators (rotifers, chironomid and insect larvae) and the presence of a very weak attachment between protozoa and sand grains.

Melt Procedure Affects the Photosynthetic Response of Sea Ice Algae

The accuracy of sea ice algal production estimates is influenced by the range of melting procedures used in studies to obtain a liquid sample for incubation, particularly in relation to the duration of melt and the approach to buffering for osmotic shock. In this research, ice algal photophysiology from 14C incubations was compared in field samples prepared by three melt procedures: i) a rapid ≤ 4 h melt of the bottommost (< 1 cm) ice algal layer scraped into a large volume of filtered seawater (salinity 27 - 30), ii) melt of a bottom 5 cm section diluted into a moderate volume of filtered seawater over 24 h (salinity 20 - 24), and iii) melt of a bottom 5 cm section without any filtered seawater dilution over about 48 h (salinity 10 -12). Maximum photosynthetic rate, photosynthetic efficiency and production at zero irradiance were significantly affected by the melt treatment employed in experiments. All variables were greatest in the highly diluted scrape sample and lowest in the bulk-ice samples melted in the absence of filtered seawater. Laboratory experiments exposing cultures of the common sea ice diatom Nitzschia frigida to different salinities and light conditions suggested that the field-based responses can be attributed to the rapid (< 4 h) adverse effects of exposing cells to low salinities during melt without dilution. The observed differences in primary production between melt treatments were estimated to account for over 60% of the variability in production estimates reported for the Arctic. Future studies are strongly encouraged to replicate salinity conditions representative of in situ values during the melting process to minimize hypoosmotic stress, thereby most accurately estimating primary production.

Soil sealing by algae: An alternative to plastic pond liners for outdoor algal cultivation

Commercial production of algal biofuels is currently limited by high capital costs, particularly costs of synthetic pond liners that minimize seepage of cultivation fluids, salts, and nutrients into the subsurface beneath outdoor algae cultivation facilities. Even some profitable nutraceutical companies bear the high costs of pond liners. However, studies of animal waste holding ponds and aquaculture facilities have shown that underlying soils can effectively “self-seal”, potentially eliminating the need for plastic liners. Here, we explored the potential for self-sealing with algae to provide an alternative to synthetic pond liners in unlined algae cultivation ponds. Laboratory-scale soil column experiments were used to investigate soil clogging by algae, a topic rarely discussed in the literature. Columns composed of fine sand, loamy sand, and loam soil displayed reductions in saturated hydraulic conductivity of the entire soil column of up to two orders of magnitude in response to infiltration by the alga Scenedesmus dimorphus suspended in algal culture nutrient solution at a density of 5 × 108 cells L−1. Scanning electron microscope imaging showed a dense algal layer on the surface of each soil column, thickly coating mineral grains with algal material and filling pore spaces. The algal coating was absent in samples at >3 cm depth in the soil columns, and measurements of chlorophyll content also confirmed that algal cells were mostly confined to the soil surface. In this study, the application of an algal suspension contributed significantly to soil sealing. This new application of biological sealing technology should be studied further to determine its utility and durability as an alternative to plastic liners, perhaps in conjunction with soil compaction to achieve hydraulic conductivities beneath algal production ponds that are protective of groundwater quality.

Intrathalline Metabolite Profiles in the Lichen Argopsis friesiana Shape Gastropod Grazing Patterns.

Lichen-gastropod interactions generally focus on the potential deterrent or toxic role of secondary metabolites. To better understand lichen-gastropod interactions, a controlled feeding experiment was designed to identify the parts of the lichen Argopsis friesiana consumed by the Subantarctic land snail Notodiscus hookeri. Besides profiling secondary metabolites in various lichen parts (apothecia, cephalodia, phyllocladia and fungal axis of the pseudopodetium), we investigated potentially beneficial resources that snails can utilize from the lichen (carbohydrates, amino acids, fatty acids, polysaccharides and total nitrogen). Notodiscus hookeri preferred cephalodia and algal layers, which had high contents of carbohydrates, nitrogen, or both. Apothecia were avoided, perhaps due to their low contents of sugars and polyols. Although pseudopodetia were characterized by high content of arabitol, they were also rich in medullary secondary compounds, which may explain why they were not consumed. Thus, the balance between nutrients (particularly nitrogen and polyols) and secondary metabolites appears to play a key role in the feeding preferences of this snail.