Size scaling of photophysiology and growth in four freshly isolated diatom species from Ryder Bay, western Antarctic peninsula

Abstract

Diatoms are one of the dominant groups in phytoplankton communities of the western Antarctic Peninsula ( WAP ). Although generally well‐studied, little is known about size dependent photophysiological responses in diatom bloom formation and succession. To increase this understanding, four Antarctic diatom species covering two orders of magnitude in cell size were isolated in northern Marguerite Bay ( WAP ). Fragilariopsis sp., Pseudo‐nitzschia cf. subcurvata , Thalassiosira cf. antarctica , and Proboscia cf. alata were acclimated to three different irradiances after which photophysiology, electron transport, carbon fixation, and growth were assessed. The small species Fragilariopsis sp., Pseudo‐nitzschia cf. subcurvata , and large species Proboscia cf. alata showed similar photoacclimation to higher irradiances with a decrease in cellular chlorophyll a and an increase in chlorophyll a specific absorption and xanthophyll cycle pigments and activity. In contrast, pigment concentrations and absorption remained unaffected by higher irradiances in the large species Thalassiosira cf. antarctica . Overall, the small species showed significantly higher growth rates compared to the large species, which was related to relatively high light harvesting capacity and electron transport rates in the smaller species. However, photophysiological responses related to photoinhibition and photoprotection and carbon fixation showed no relationship with cell size. This study supports the dominance of small diatoms at low irradiances during winter and early spring, but does not provide photophysiological evidence for the dominance of large diatoms during the phytoplankton bloom in the WAP . This suggests that other factors such as grazing and nutrient availability are likely to play a major role in diatom bloom formation.

Response to Sea Ice Melt Indicates High Seeding Potential of the Ice Diatom Thalassiosira to Spring Phytoplankton Blooms: A Laboratory Study on an Ice Algal Community From the Sea of Okhotsk

“…Mean values (±SD) are the average of four independent measurements. P. glacialis under similar conditions were consistent and around 0.3 day −1 (Gilstad and Sakshaug, 1990;Kulk et al, 2019). While reported maximum growth rate for pennate diatoms were around 0.2 day −1 and was mainly collected from Fragilariopsis cylindrus and Nitzschia frigida, two representative pennate diatoms of the polar regions (Hegseth, 1992;Juhl and Krembs, 2010;Aslam et al, 2012Aslam et al, , 2018.…”

“…The saturating pulse was provided by a red-LED with a peak illumination at 655 nm and set at 7,000 µmol photons m −2 s −1 and lasted for 400 ms for all measurements (Yan et al, 2019). The maximum photochemical efficiency of PSII was calculated as mainly contributed by the centric diatoms and was slightly lower than the maximum growth rate of ice diatom isolates or communities under similar temperature, salinity and light conditions reported in previous studies (Gilstad and Sakshaug, 1990;Hegseth, 1992;Juhl and Krembs, 2010;Aslam et al, 2012Aslam et al, , 2018Olsen et al, 2017;Kulk et al, 2019). In those studies, the maximum growth rates of T. antarctica, T. nordenskioeldii, and FIGURE 7 | Abundances of rbcL (cDNA) normalized to the gene copy number (cDNA/DNA) during the incubation.…”

Microbial Community Structure Driven by a Volcanic Gradient in Glaciers of the Antarctic Archipelago South Shetland

“…Organic compounds in glacier ice must be biologically synthesized by CO 2 fixation by phototrophs, i.e., the microeukaryotes Thalassiosira antarctica and Hydrurus foetidus identified in ROJ and MAC samples or chemolithotrophs such as Streptomyces [ 45 , 46 ]. In our research, we have also identified some aerobic CO oxidizers as Corynebacterium [ 47 ], especially in the eastern glaciers.…”

Shifts in growth light optima among diatom species support their succession during the spring bloom in the Arctic

“…With this objective, we grew five ecologically relevant Arctic (or bipolar) diatom species under a range of limiting, saturating and supersaturating light typical of their respective habitats, and documented changes in their growth rates, photophysiology and carbon fixation capabilities. Most knowledge on Arctic diatom photoadaption at the moment is (i) inferred from correlation‐based field observations (Kvernvik et al, 2021; Lewis et al, 2019; Schuback et al, 2017), (ii) assembled from independent studies targeting diverse photoadaptative traits in different polar species [reviewed by Lacour et al (2017)] and/or (iii) extrapolated from laboratory studies in which most taxa occur only in Antarctic (Kulk et al, 2019; Petrou et al, 2011; Strzepek et al, 2019). However, we lack studies describing dose–response relationships between environmental factors and diverse species dominating distinct niches over seasonal dynamics required by production models and ecological theory.…”

“…These pathways are usually more active under high light and provide photoprotection(Wagner et al, 2016), but not always, as for instance cyclic electron flow around PSI is constitutive in green organisms(Munekage et al, 2004), a pathway suspected of having an enhanced rate in F. cylindrus compared to temperate diatom counterparts(Goldman et al, 2015). Interestingly,Kulk et al (2019), described a 2.5-fold increase in electron requirement per C fixed under limiting growth light in two out of four Antarctic diatom species, including Fragilariopsis sp. Coinciding with F. cylindrus being the only species for which we observed decreasing α* under the lowest gE in this study.4.2 | Contrasts in C-specific productivity among species and depending upon growth light intensityData on C-specific 14 C-uptake also reflected a photoadaptation gradient, with the lowest P C M in sympagic N. frigida and maximal P C M in open-water C. neogracilis.…”