Ecophysiological and Cell Biological Traits of Benthic Diatoms From Coastal Wetlands of the Southern Baltic Sea

Terrestrial Trentepohlia sp. (Ulvophyceae) from alpine and coastal collection sites show strong desiccation tolerance and broad light and temperature adaptation

For the present study, we collected the Ulvophyceae species Trentepohlia aurea from limestone rock near Berchtesgaden, Germany, and the closely related taxa T. umbrina from Tilia cordata tree bark and T. jolithus from concrete wall both in Rostock, Germany. Freshly sampled material stained with Auramine O, DIOC6, and FM 1-43 showed an intact physiological status. Cell walls were depicted with calcofluor white and Carbotrace. When subjected to three repeated and controlled cycles of desiccation over silica gel (~ 10% relative humidity) followed by rehydration, T. aurea recovered about 50% of the initial photosynthetic yield of photosystem II (YII). In contrast, T. umbrina and T. jolithus recovered to 100% of the initial YII. HPLC and GC analysis of compatible solutes found highest proportions of erythritol in T. umbrina and mannitol/arabitol in T. jolithus. The lowest total compatible solute concentrations were detected in T. aurea, while the C/N ratio was highest in this species, indicative of nitrogen limitation. The prominent orange to red coloration of all Trentepohlia was due to extremely high carotenoid to Chl a ratio (15.9 in T. jolithus, 7.8 in T. aurea, and 6.6. in T. umbrina). Photosynthetic oxygen production was positive up to ~ 1500 µmol photons m-2 s-1 with the highest Pmax and alpha values in T. aurea. All strains showed a broad temperature tolerance with optima for gross photosynthesis between 20 and 35 °C. The presented data suggest that all investigated Trentepohlia species are well adapted to their terrestrial lifestyle on exposed to sunlight on a vertical substrate with little water holding capacity. Nevertheless, the three Trentepohlia species differed concerning their desiccation tolerance and compatible solute concentrations. The lower compatible solute contents in T. aurea explain the incomplete recovery of YII after rehydration.

Photosynthetic, Respirational, and Growth Responses of Six Benthic Diatoms from the Antarctic Peninsula as Functions of Salinity and Temperature Variations

Temperature and salinity are some of the most influential abiotic parameters shaping biota in aquatic ecosystems. In recent decades, climate change has had a crucial impact on both factors—especially around the Antarctic Peninsula—with increasing air and water temperature leading to glacial melting and the accompanying freshwater increase in coastal areas. Antarctic soft and hard bottoms are typically inhabited by microphytobenthic communities, which are often dominated by benthic diatoms. Their physiology and primary production are assumed to be negatively affected by increased temperatures and lower salinity. In this study, six representative benthic diatom strains were isolated from different aquatic habitats at King George Island, Antarctic Peninsula, and comprehensively identified based on molecular markers and morphological traits. Photosynthesis, respiration, and growth response patterns were investigated as functions of varying light availability, temperature, and salinity. Photosynthesis−irradiance curve measurements pointed to low light requirements, as light-saturated photosynthesis was reached at <70 µmol photons m−2 s−1. The marine isolates exhibited the highest effective quantum yield between 25 and 45 SA (absolute salinity), but also tolerance to lower and higher salinities at 1 SA and 55 SA, respectively, and in a few cases even <100 SA. In contrast, the limnic isolates showed the highest effective quantum yield at salinities ranging from 1 SA to 20 SA. Almost all isolates exhibited high effective quantum yields between 1.5 °C and 25 °C, pointing to a broad temperature tolerance, which was supported by measurements of the short-term temperature-dependent photosynthesis. All studied Antarctic benthic diatoms showed activity patterns over a broader environmental range than they usually experience in situ. Therefore, it is likely that their high ecophysiological plasticity represents an important trait to cope with climate change in the Antarctic Peninsula.

Photosynthesis, Respiration, and Growth of Five Benthic Diatom Strains as a Function of Intermixing Processes of Coastal Peatlands with the Baltic Sea

In light of climate change, renaturation of peatlands has become increasingly important, due to their function as carbon sinks. Renaturation processes in the Baltic Sea include removal of coastal protection measures thereby facilitating exchange processes between peatland and Baltic Sea water masses with inhabiting aquatic organisms, which suddenly face new environmental conditions. In this study, two Baltic Sea and three peatland benthic diatom strains were investigated for their ecophysiological response patterns as a function of numerous growth media, light, and temperature conditions. Results clearly showed growth stimulation for all five diatom strains when cultivated in peatland water-based media, with growth dependency on salinity for the Baltic Sea diatom isolates. Nutrient availability in the peatland water resulted in higher growth rates, and growth was further stimulated by the carbon-rich peatland water probably facilitating heterotrophic growth in Melosira nummuloides and two Planothidium sp. isolates. Photosynthesis parameters for all five diatom strains indicated low light requirements with light saturated photosynthesis at <70 µmol photons m−2 s−1 in combination with only minor photoinhibition as well as eurythermal traits with slightly higher temperature width for the peatland strains. Growth media composition did not affect photosynthetic rates.