Photosynthesis and Respiration of Baltic Sea Benthic Diatoms to Changing Environmental Conditions and Growth Responses of Selected Species as Affected by an Adjacent Peatland (Hütelmoor)

Abstract

Eight benthic diatom taxa ( Actinocyclus octonarius , Melosira moniliformis , Halamphora sp. 1, Halamphora sp. 2, Navicula perminuta , Navicula phyllepta , Nitzschia dubiiformis , Nitzschia pusilla ) were isolated from sediments sampled in the southern coastal brackish Baltic Sea and established as unialgal cultures. The coastal shallow water sampling area lies close to a fen peat site (Hütelmoor) and both are connected through an underground peat layer, which might facilitate organic matter and nutrient fluxes along the terrestrial-marine gradient. The photosynthetic performance of these diatoms was measured at different photon fluence rates (0–1200 μmol photons m –2 s –1 , always recorded at 20°C) and different temperatures (5–40°C, always measured at saturating ∼270 μmol photons m –2 s –1 ), resulting in light saturation points between 32 and 151 μmol photons m –2 s –1 and maximum net primary production rates of 23–144 μmol O 2 mg –1 Chl a h –1 . None of the species showed severe photoinhibition, and hence all displayed a high photo-physiological plasticity. Photosynthetic oxygen evolution and respirational oxygen consumption between 5 and 40°C revealed eurythermal traits for half of the studied taxa as photosynthetic efficiency was at least 20% of the maximum values at the extreme temperatures. The remaining taxa also indicated eurythermal characteristics, however, photosynthetic efficiency of at least 20% was at a narrower temperature range [5 (10) °C to 30 (35) °C]. Species-specific optimum temperatures for photosynthesis (15–30°C) were always lower compared to respiration (25–40°C). Actinocyclus octonarius and Nitzschia dubiiformis were grown in different defined media, some enriched with Hütelmoor water to test for possible effects of organic components. Hütelmoor water media stimulated growth of both diatom species when kept in a light dark cycle. Actinocyclus octonarius particularly grew in darkness in Hütelmoor water media, pointing to heterotrophic capabilities. The benthic diatoms studied are characterized by high photo-physiological plasticity and a broad temperature tolerance to maintain high primary production rates under wide environmental fluctuations. Organic carbon fluxes from the Hütelmoor into the Baltic Sea may support mixo- and/or heterotrophic growth of microphytobenthic communities. These are essential traits for living in a highly dynamic and variable shallow water environment at the coastal zone of the Baltic Sea.

The Effect of Abiotic Factors on Abundance and Photosynthetic Performance of Airborne Cyanobacteria and Microalgae Isolated from the Southern Baltic Sea Region

“…Halamphora sp., isolated from the Baltic Sea, has a wide temperature range of 15–25 °C, but a 30 °C-preferring strain has also been isolated. By higher temperatures, the authors noted a decrease in photosynthesis [ 35 ]. Moreover, high numbers of cells (above 30 × 10 5 cell mL −1 ) were also recorded for diatoms Nitzschia sp.…”

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

“…Only very low (4 • C) or very high (40 • C) temperatures strongly reduced the growth rates of benthic diatoms (Scholz and Liebezeit, 2012). Few studies have been undertaken so far on the influence of temperature on photosynthesis and respiration of benthic diatoms in the Baltic Sea (Woelfel et al, 2014;Prelle et al, 2019). The data of these authors indicate at least 20% photosynthetic efficiency from 5 to 35 • C, confirming eurythermal traits.…”

“…Photosynthesis-irradiance (PI)-curves of the four diatom strains were measured according to Prelle et al (2019). Shortly, 3 ml of thin log phase algal suspension (to avoid selfshading chlorophyll a content was kept at 1,270 µg/l on average) of each strain and 30 µl sodium bicarbonate (NaHCO 3 2 mM final concentration) were added to four airtight watertempered (20 • C) oxygen electrode chambers (DW1, Hansatech Instruments, King's Lynn, United Kingdom).…”

“…However, there are still species-specific optima found, as N. filiformis was the only strain showing positive oxygen production over the whole range of temperatures. Prelle et al (2019) used the same methodical approach to study the temperature dependent oxygen production in eight benthic diatom species from the southern Baltic Sea. Similar to the present study, they found that the optimum temperature for photosynthesis was lower compared to respiration.…”

Ecophysiological, morphological, and biochemical traits of free-living Diplosphaera chodatii (Trebouxiophyceae) reveal adaptation to harsh environmental conditions

“…Photosynthetic oxygen evolution rates of D. chodatii were measured under increasing photon flux densities from 0 to 1580 μmol photons m −2 s −1 according to Karsten et al (2010b) and Prelle et al (2019). Presens Fibox3 oxygen optodes (Presens, Germany) and 4 × 3 mL thermostatic acrylic chambers DW1 (Hansatech Instruments, UK) combined with magnetic stirrers were used at an ambient temperature of 20°C…”