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Increased temperature and ocean acidification are two main factors threatening Arctic coastal ecosystems. To explore the consequences of increased average temperature and ocean acidification in Kongsfjorden, the performance of six common species of macroalgae, the chlorophyte Monostroma arcticum, the rhodophytes Phycodrys rubens, and Ptilota plumosa, and the phaeophytes Alaria esculenta, Desmarestia aculeata and Saccorhiza dermatodea, was tested after 9 days of culture at 4 and 10 °C in combination with current (ca. 390 ppmv) and future (1000 ppmv) levels of atmospheric CO under solar radiation in summer. Temperature affected mainly the photosynthetic performance as measured by PAM fluorescence, particularly the initial slope ( α) of ETR curves, the light saturation parameter ( E ), and F / F values, as well as the protein content, especially in the phaeophytes. On the other hand, CO affected mainly the internal accumulation of carbohydrates and lipids. The C:N balance was largely unaffected. External carbonic anhydrase activity was not inhibited at high CO, and nitrate reductase activity remained unaffected. The resulting growth rate was not altered by treatments in three out of the six species studied. On the other hand, P. rubens showed a positive effect of increasing temperature, D. aculeata was negatively influenced by CO, and S. dermatodea was positively affected by CO. Significant interactions between CO and temperature were found in 20 % of the analyses. Whether additive or synergistic, the co-occurrence of a higher temperature with other stressors such as elevated CO increases the probability of community changes by modifying the performance of these species. [ABSTRACT FROM AUTHOR]

Despite the high productivity and ecological importance of seaweeds in polar coastal regions, little is known about their carbon utilization mechanisms, especially the kinetics of the CO2-fixing enzyme Rubisco. We analyzed Rubisco carboxylation kinetics at 4 °C and 25 °C in 12 diverse polar seaweed species (including cold-temperate populations of the same species) and the relationship with their ability to use bicarbonate, by using 13C isotope discrimination and pH drift experiments. We observed a large variation in Rubisco carboxylation kinetics among the selected species, although no correlation was found between either the Michaelis–Menten constant for CO2 (K c) or Rubisco content per total soluble protein ([Rubisco]/[TSP]) and the ability to use bicarbonate for non-green seaweeds. This study reports intraspecific Rubisco cold adaptation by means of either higher Rubisco carboxylation turnover rate (k catc) and carboxylase efficiency (k catc/ K c) at 4 °C or higher [Rubisco]/[TSP] in some of the analyzed species. Our data point to a widespread ability for photosynthetic bicarbonate usage among polar seaweeds, despite the higher affinity of Rubisco for CO2 and higher dissolved CO2 concentration in cold seawater. Moreover, the reported catalytic variation within form ID Rubisco might avert the canonical trade-off previously observed between K c and k catc for plant Rubiscos. [ABSTRACT FROM AUTHOR]

Ocean acidification and warming are affecting polar regions with particular intensity. Rocky shores of the Antarctic Peninsula are dominated by canopy-forming Desmarestiales. This study investigates the physiological and transcriptomic responses of the endemic macroalga Desmarestia anceps to a combination of different levels of temperature (2 and 7 °C), dissolved CO2 (380 and 1000 ppm), and irradiance (65 and 145 μmol photons m-2 s-1). Growth and photosynthesis increased at high CO2 conditions, and strongly decreased at 2 °C plus high irradiance, in comparison to the other treatments. Photoinhibition at 2 °C plus high irradiance was evidenced by the photochemical performance and intensive release of dissolved organic carbon. The highest number of differentially regulated transcripts was observed in thalli exposed to 2 °C plus high irradiance. Algal 13C isotopic discrimination values suggested an absence of down-regulation of carbon-concentrating mechanisms at high CO2. CO2 enrichment induced few transcriptomic changes. There was high and constitutive gene expression of many photochemical and inorganic carbon utilization components, which might be related to the strong adaptation of D. anceps to the Antarctic environment. These results suggest that increased temperature and CO2 will allow D. anceps to maintain its productivity while tolerating higher irradiances than at present conditions. [ABSTRACT FROM AUTHOR]

Ocean acidification affects with special intensity Arctic ecosystems, being marine photosynthetic organisms a primary target, although the consequences of this process in the carbon fluxes of Arctic algae are still unknown. The alteration of the cellular carbon balance due to physiological acclimation to an increased CO concentration (1300 ppm) in the common Arctic brown seaweeds Desmarestia aculeata and Alaria esculenta from Kongsfjorden (Svalbard) was analysed. Growth rate of D. aculeata was negatively affected by CO enrichment, while A. esculenta was positively affected, as a result of a different reorganization of the cellular carbon budget in both species. Desmarestia aculeata showed increased respiration, enhanced accumulation of storage biomolecules and elevated release of dissolved organic carbon, whereas A. esculenta showed decreased respiration and lower accumulation of storage biomolecules. Gross photosynthesis (measured both as O evolution and C fixation) was not affected in any of them, suggesting that photosynthesis was already saturated at normal CO conditions and did not participate in the acclimation response. However, electron transport rate changed in both species in opposite directions, indicating different energy requirements between treatments and species specificity. High CO levels also affected the N-metabolism, and C isotopic discrimination values from algal tissue pointed to a deactivation of carbon concentrating mechanisms. Since increased CO has the potential to modify physiological mechanisms in different ways in the species studied, it is expected that this may lead to changes in the Arctic seaweed community, which may propagate to the rest of the food web. [ABSTRACT FROM AUTHOR]