Explore the vast range of titles available.

Macroalgae such as kelp are important ecosystem engineers in the Polar Regions and potentially affected by freshening and ocean warming. The endemic Arctic kelp Laminaria solidungula might be particularly imperiled and become locally extinct from Arctic fjord systems in the future, since temperature increase is most pronounced in the Polar Regions. Additionally, increased temperatures cause glacier and sea ice melting and enhancing terrestrial run-off from snowfields, which eventually can result in hyposaline conditions in fjord systems. We conducted a multiple-stressor experiment at four temperatures (0, 5, 10, 15 °C) and two salinities (SA 25, 35) to investigate the combined effects of increasing temperature and decreasing salinities on the physiological and biochemical status of young L. solidungula sporophytes. Both drivers had significant and interacting impacts, either in an additive or antagonistic way, dependent on the respective response variable. The maximum quantum yield of photosystem II (Fv/Fm) significantly declined with temperature increase and low salinity. Even though the absolute pigment content was not affected, the deepoxydation state of the xanthophyll cycle increased with intensified stress. Higher temperatures affected the C:N ratio significantly, mainly due to reduced nitrogen uptake, while SA 25 supported the nitrogen uptake, resulting in an attenuation of the effect. The concentration of mannitol decreased at SA 25. At control SA 35 mannitol level remained steady between 0 and 10 °C but significantly decreased at 15 °C. Conclusively, our results show that L. solidungula is very susceptible to both drivers of climate change, especially when they are combined. Implications to species ecology are discussed.

In coastal zones, salinity is commonly a rather local environmental factor that can be highly variable. Future climate change scenarios indicate for many coastal regions besides warming also changes in current salinity regime due to less precipitation, higher evaporation, or more freshwater run-off, resulting in decreasing or increasing saline conditions. The soft bottom of shallow water coastal zones is typically inhabited by benthic diatoms which cover as photosynthetic biofilms extensive areas of sediments. Cylindrotheca closterium is a cosmopolitan and abundant taxon of such communities, and is widely used as a benthic diatom model system. Nevertheless, comprehensive ecophysiological data on the salinity tolerance of this ecologically important benthic species are still missing. Therefore, the main goal was to investigate the salinity tolerance in 6 strains of C. closterium from 5 different clades and from marine to brackish habitats. An analysis of growth as function of salinity allowed the evaluation of tolerance limits, growth optima, and acclimation abilities of individual strains. The data documented isolate-specific growth response patterns and rather broad tolerance widths among the six strains of C. closterium, which point to strong genotypic differentiation. The results of the phylogenetic network analysis indicate several well separated grades within C. closterium, thereby supporting the earlier suggestion of a cryptic species complex.

Soil P pools are strongly driven by microbial activities, and vice versa, P pools shape bacterial communities and their functional potential. Biological soil crusts (biocrusts) represent a microbial hotspot for nutrient turnover. We compared biocrusts and bulk soil samples from different temperate beech (Fagus sylvatica L.) forests representing a gradient in soil texture, nutrient concentrations, and pH values at biocrust peak biomass. We measured the total and plant-available P and N concentrations and assessed the bacterial potential to mineralize (phoD, phnX), solubilize (gcd), and take up P (pstS and pitA) and mineralize (chiA, apr) and fix N (nifH) by quantifying the respective marker genes (qPCR). We found an increase of absolute and relative bacterial abundance involved in P turnover in biocrusts, but the strategy to acquire P differed between the regions as bacteria harboring the starvation-induced pstS gene were most abundant where labile P was lowest. In contrast, the region with lowest total P concentrations has a higher potential to utilize more stable phosphonates. N mineralization was strongly correlated to P turnover at regions with increased labile N and P concentrations. Interestingly, the potential to fix N was highest in the bulk soil where total P concentrations were highest. Even though the correlation of N and P turnover is strongest if their ratio is low, the acquisition strategy strongly depends on soil properties.

The polysaccharide laminarin (β-1,3-glucan) is used as a long-term carbon storage compound in brown algae. This chemical storage form of carbon enables perennial brown algae in seasonally fluctuating ecosystems to uncouple growth from photosynthesis, i.e., most of these plants grow as seasonal anticipators in winter based on remobilization of laminarin, while in summer, growth typically ceased to fill up the storage pool. Because of this high ecological relevance, a reliable and precise method for determination and quantification of laminarin is needed. Therefore, a simple, efficient, cold water extraction method coupled to a new quantitative liquid chromatography-mass spectrometrical method (LC-MS) was developed. Laminarin was determined in 9 out of 12 brown algal species, and its expected typical molar mass distribution of 2000–7000 Da was confirmed. Furthermore, laminarin consisted of a complex mixture of different chemical forms, since 15 chemical laminarin species with distinct molecular weights were measured in 9 species of brown algae. Differences in chain length and number of laminarin species seem to be species specific and hence may indicate some chemotaxonomic value. Laminarin concentrations in the algal tissues ranged from 0.03 to 0.86 % dry weight (DW). The direct chemical characterization and quantification of laminarin by LC-MS represents a powerful method to verify the biochemical and ecological importance of laminarin for brown algae.

Single-celled green algae within the Trebouxiophyceae (Chlorophyta) are typical components of terrestrial habitats, which often exhibit harsh environmental conditions for these microorganisms. This study provides a detailed overview of the ecophysiological, biochemical, and ultrastructural traits of an alga living on tree bark. The alga was isolated from a cypress tree in the Botanical Garden of Innsbruck (Austria) and identified by morphology and molecular phylogeny as Diplosphaera chodatii. Transmission electron microscopy after high-pressure freezing (HPF) showed an excellent preservation of the ultrastructure. The cell wall was bilayered with a smooth inner layer and an outer layer of polysaccharides with a fuzzy hair-like appearance that could possibly act as cell-cell adhesion mechanism and hence as a structural precursor supporting biofilm formation together with the mucilage observed occasionally. The photosynthetic-irradiance curves of D. chodatii indicated low light requirements without photoinhibition at high photon flux densities (1580 μmol photons m−2 s−1) supported by growth rate measurements. D. chodatii showed a high desiccation tolerance, as 85% of its initial value was recovered after controlled desiccation at a relative humidity of ~10%. The alga contained the low molecular weight carbohydrates sucrose and sorbitol, which probably act as protective compounds against desiccation. In addition, a new but chemically not elucidated mycosporine-like amino acid was detected with a molecular mass of 332 g mol−1 and an absorption maximum of 324 nm. The presented data provide various traits which contribute to a better understanding of the adaptive mechanisms of D. chodatii to terrestrial habitats.

Members of the cosmopolitan green algal genus Klebsormidium (Klebsormidiales, Streptophyta) are typical components of terrestrial microbiotic communities such as biological soil crusts, which have many important ecological functions. In the present study, Klebsormidium dissectum (Gay) Ettl & Gärtner was isolated from a high alpine soil crust in the Tyrolean Alps, Austria. Physiological performance in terms of growth and photosynthesis was investigated under different controlled abiotic conditions and compared with ultrastructural changes under the treatments applied. dissectum showed very low light requirements as reflected in growth patterns and photosynthetic efficiency.Increasing temperatures from 5 ° C to 40 ° C led to different effects on respiratory oxygen consumption and photosynthetic oxygen evolution. While at low temperatures (5-10 ° C), respiration was not detectable or on a very low level, photosynthesis was relatively high, Reversely, at the highest temperature, respiration was unaffected, and photosynthesis strongly inhibited pointing to strong differences in temperature sensitivity between both physiological processes.Although photosynthetic performance of dissectum was strongly affected under short-term desiccation and recovered only partly after rehydration, this species was capable to survive even 3 weeks at 5% relative air humidity. K. dissectum cells have a cell width of 5.6 ± 0.3 µm. and a cell length of 8.4 ± 2.0 µm. Desiccated cells showed a strongly reduced cell width (46% of control) and cell length (65% of control). In addition, in desiccated cells, fewer mitochondria were stained by DIOC₆, and damaged plasma membranes were detected by FM 1-43 staining. High-pressure freeze fixation as well as chemical fixation allowed visualizing ultrastructural changes caused by desiccation. In such cells, the nucleus and chloroplast were still visibly intact, but the extremely thin cell walls (75-180 nm) were substantially deformed. The cytoplasm appeared electron dense and mitochondria were altered. Although K. dissectum can be characterized as euryoecious species, all ecophysiological and ultrastructural data indicate susceptibility to desiccation. However, the steadily occurring fragmentation of filaments into smaller units leads to improved self protection and thus may represent a life strategy to better survive longer periods of drought in exposed alpine soil crusts.

Intertidal algae have to cope with diurnally and seasonally fluctuating environmental factors such as salinity, temperature, dehydration, and light. In New Zealand, solar radiation, including the ultraviolet wavelengths, is also an important stress factor for such algae. Therefore, two native (Bostrychia arbuscula W.H.Harvey [Ceramiales], Champia novae-zelandiae (J.D.Hooker & Harvey) Harvey [Rhodymeniales]) and one introduced red algal taxon (Schizymenia spp. J. Agardh [Nemastomatales]) were investigated over 12 months in terms of stress metabolites which contribute to ultraviolet radiation (UVR) and salinity tolerance. Mycosporine-like amino acids (MAAs), which act as sunscreens, and organic osmolytes were qualitatively and quantitatively analyzed. Porphyra-334, shinorine, and palythine were the most dominant MAAs yet distributed differently among the species. B. arbuscula showed a correlation between photosynthetically active radiation (PAR)/UVR and slightly higher MAA concentrations in summer. In contrast, C. novae-zelandiae displayed the lowest level of MAAs in summer, and no correlation was found between MAA values and solar radiation. In Schizymenia spp., the highest MAA amounts were found in summer, and for most months, a correlation with PAR/UV radiation was visible. While digeneaside and sorbitol were the dominant organic osmolytes in B. arbuscula, floridoside occurred in C. novae-zelandiae and Schizymenia spp. Only B. arbuscula exhibited higher organic osmolyte concentrations in summer. In contrast, floridoside contents in C. novae-zelandiae and Schizymenia spp. were low and highly variable over the course of the seasons. Our data indicate that both native red algal species are well acclimated to the intertidal zone. For the introduced Schizymenia spp., a more narrow salinity tolerance can be assumed, while the high MAA values may explain its establishment in New Zealand.

This study aimed to investigate the presence and diversity of fungal parasites in Arctic coastal microphytobenthic communities. These communities represent a key component in the functioning of Arctic trophic food webs. Fungal parasites, particularly Chytridiomycota (chytrids), play significant roles by controlling microalgal bloom events, impacting genetic diversity, modifying microbial interactions, and accelerating nutrient and energy transfer to higher trophic levels. In the context of rapid Arctic warming and increased glacier meltwater, which significantly affects these communities, we used high-throughput sequencing to explore fungal community composition. Our results show that chytrids dominate fungal communities in Arctic benthic habitats and that the overall fungal diversity is primarily influenced by the salinity gradient. Chytrid representation is positively correlated with the presence of potential benthic diatom ( Surirella , Nitzschia , Navicula ) and green algae (Ulvophyceae) hosts, while microscopic observations provide further evidence for the presence of active chytrid infections.

MAIN CONCLUSION : We introduced a novel combination of chromatographic techniques for the purification and analysis of a new UV-sunscreen mycosporine-like amino acid (MAA) in the terrestrial green alga Prasiola calophylla. Prasiola calophylla (Carmichael ex Greville) Kützing (Trebouxiophyceae, Chlorophyta) is a typical member of terrestrial algal communities in temperate Europe, where it regularly experiences various stress conditions including strong diurnal and seasonal fluctuations in ultraviolet radiation (UVR). As a photoprotective mechanism Prasiola species and other related Trebouxiophycean taxa synthesize a mycosporine-like amino acid (MAA) as natural sunscreen whose chemical structure was unknown so far. In the present study a new methodological approach is described for the isolation, purification and structural elucidation of this novel sunscreen in P. calophylla. The new compound exhibits an absorption maximum at 324 nm (in the short ultraviolet-A), a molecular weight of 333 and a molecular extinction coefficient of 12.393 M⁻¹ cm⁻¹, and could be identified as N-[5,6 hydroxy-5(hydroxymethyl)-2-methoxy-3-oxo-1-cycohexen-1-yl] glutamic acid using one- and two-dimensional ¹H and ¹³C-NMR spectroscopy. As trivial name for this novel MAA we suggest ‘prasiolin’. The ecologically essential function of prasiolin for UVR-protection in terrestrial algae of the Trebouxiophyceae is discussed.

The keystone macroalga Fucus vesiculosus (Phaeophyceae), dominating shallow hard bottom zones, encounters a strongly and rapidly changing environment due to anthropogenic change over the last decades in the Baltic Sea. Thus, in four successive benthic mesocosm experiments, the single and joint effects of increased temperature (Δ + 5 °C) and pCO2 (1100 ppm) under ambient irradiances were experimentally tested on the antioxidative properties of western Baltic F. vesiculosus in all seasons. The antioxidative properties (superoxide dismutase activity and lipid peroxidation) as well as the sensitivity of F. vesiculosus photosynthetic performance (i.e., effective quantum yield) to oxidative stress under these global change scenarios were seasonally examined. F. vesiculosus exhibited high and relatively constant photosynthetic performance under artificial hydrogen peroxide (H2O2) stress in all seasons. High activities of superoxide dismutase and a relatively low degree of the biomarker for lipid peroxidation (malondialdehyde concentration) were found in F. vesiculosus. Thus, Baltic F. vesiculosus is equipped with a high antioxidative potential to tolerate strong oxidative stress for at least short periods. Antioxidative properties of F. vesiculosus were more strongly affected by warming than by acidification, resulting in significantly increased malondialdehyde concentrations under elevated temperature levels in all seasons. Oxidative stress was enhanced in F. vesiculosus under warming but seem to be modulated by seasonally varying environmental conditions (e.g., high and low irradiances) and pCO2 levels. However, more frequent summer heatwaves reaching and surpassing lethal temperatures in shallow coastal waters may determine the F. vesiculosus population’s overall persistence in the Baltic Sea.