Yukiko Tanabe

COMPARATIVE STUDY ON THE PHOTOSYNTHETIC PROPERTIES OF PRASIOLA (CHLOROPHYCEAE) AND NOSTOC (CYANOPHYCEAE) FROM ANTARCTIC AND NON‐ANTARCTIC SITES1

The terrestrial cyanobacterium Nostoc commune Vaucher ex Bornet et Flahault occurs worldwide, including in Japan and on the Antarctic continent. The terrestrial green alga Prasiola crispa (Lightf.) Kütz. is also distributed in Antarctica. These two species need to acclimate to the severe Antarctic climate including low ambient temperature and desiccation under strong light conditions. To clarify this acclimation process, the physiological characteristics of the photosynthetic systems of these two Antarctic terrestrial organisms were assessed. The relative rate of photosynthetic electron flow in N. commune collected in Japan and in Antarctica reached maxima at 900 and 1,100 μmol photons · m−2 · s−1, respectively. The difference seemed to reflect the presence of high amounts of UV‐absorbing substances within the Antarctic cyanobacterium. On the other hand, the optimal temperatures for photosynthesis at the two locations were 30°C–35°C and 20°C–25°C, respectively. This finding suggested a decreased photosynthetic thermotolerance in the Antarctic strain. P. crispa exhibited desiccation tolerance and dehydration‐induced quenching of PSII fluorescence. Re‐reduction of the photooxidized PSI reaction center, P700, was also inhibited at fully dry states. Photosynthetic electron flow in P. crispa reached a maximum at 20°C–25°C and at a light intensity of 700 μmol photons ḃ m−2 ḃ s−1. Interestingly, the osmolarity of P. crispa cells suggested that photosynthesis is performed using water absorbed in a liquid form rather than water absorbed from the air. Overall, these data suggest that these two species have acclimated to optimally photosynthesize under conditions of the highest light intensity and the highest temperature for their habitat in Antarctica.

In situ photochemical activity of the phytobenthic communities in two Antarctic lakes

Photochemical activity of phytobenthic communities in two freshwater lakes in East Antarctica was estimated using a submersible pulse-amplitude modulation (PAM) chlorophyll fluorometer, to answer the following questions: (1) Are the communities under bright summer photosynthetically active radiation (PAR) photosynthetically active? (2) If active, which community shows the most active signals? (3) Where is the most productive part (or depth) in the lake? Our limnological measurements indicated the two lakes were ultra-oligotrophic. Diving observations revealed that the phytobenthos of the lakes was moss-dominated which had different life-forms (moss shoots in shallow depths of both lakes, moss-pillars in the shallow lake, pinnacle moss-microbial complex community in the deeper lake). In addition, various mat-forming microbial communities inhabited the lake beds. In situ measurements of photochemical parameters indicated that shoots of mosses living just below the littoral slope, and the apical part of the moss pillars, had the highest photosynthetic activity in open water summer conditions, but mat-forming microbial communities and the other moss-microbial complex communities, showed rather lower activity. Most of the mat-forming phytobenthos surface also showed positive photosynthetic activity, but there were some cases of negligible signals in the shallow depth. This suggests that the photosynthetic activities of mat-forming communities in the shallow water were suppressed by strong ambient light in summer.

Utilizing the Effective Xanthophyll Cycle for Blooming of Ochromonas smithii and O. itoi (Chrysophyceae) on the Snow Surface

Snow algae inhabit unique environments such as alpine and high latitudes, and can grow and bloom with visualizing on snow or glacier during spring-summer. The chrysophytes Ochromonas smithii and Ochromonas itoi are dominant in yellow-colored snow patches in mountainous heavy snow areas from late May to early June. It is considered to be effective utilizing the xanthophyll cycle and holding sunscreen pigments as protective system for snow algae blooming in the vulnerable environment such as low temperature and nutrients, and strong light, however the study on the photoprotection of chrysophytes snow algae has not been shown. To dissolve how the chrysophytes snow algae can grow and bloom under such an extreme environment, we studied with the object of light which is one point of significance to this problem. We collected the yellow snows and measured photosynthetically active radiation at Mt. Gassan in May 2008 when the bloom occurred, then tried to establish unialgal cultures of O. smithii and O. itoi, and examined their photosynthetic properties by a PAM chlorophyll fluorometer and analyzed the pigment compositions before and after illumination with high-light intensities to investigate the working xanthophyll cycle. This experimental study using unialgal cultures revealed that both O. smithii and O. itoi utilize only the efficient violaxanthin cycle for photoprotection as a dissipation system of surplus energy under prolonged high-light stress, although they possess chlorophyll c with diadinoxanthin.

Abundance of benthic copepods in a saline lake in East Antarctica

Antarctic lake ecosystems have an abundance of primary producers, including benthic algae and mosses. Despite this, many of the lakes, particularly those in East Antarctica, are deporporate of fauna. This may be due, in part, to the relatively young age of many lakes in the region. The majority of Antarctic lakes were created by glacial activity following the Last Glacial Maximum (LGM), which may not have allowed suYcient time for animal groups to invade and colonize these lakes from other Antarctic ecosystems. Few studies have reported the occurrence of crustaceans in East Antarctic lakes (Burton and Hamond 1981; Bayly and Eslake 1989; summarized by Gibson and Bayly 2007). Given the lack of research, the distribution, abundance, and ecology of such organisms within Antarctica remains unclear. The 38th Japanese Antarctic Research Expedition (JARE) reported Wnding copepods in the sediments of Lake Nurume Ike, a thalassohaline meromictic lake on the Sôya Coast in the Langhovde region of East Antarctica (Fig. 1) (Seto 2001). Subsequently, several attempts were made to collect copepods from the lake using a conventional zooplankton net, hauled both vertically and horizontally. These eVorts failed to capture copepods or any other metazoan plankton. On the contrary, microscopic analysis of the copepods collected from the sediment samples suggested that they were morphologically similar to Harpacticoida, a ‘benthic copepoda’ (Dr. Kikuchi, personal communication). A conventional net haul is unlikely to capture such benthic organisms. Therefore, during the summer period of the 49th JARE we used a modiWed ‘NIPR-1’ propeller net (Fukuchi et al. 1979) to quantitatively sample for organisms living in the water-sediment interface in Lake Nurume Ike. The modiWed NIPR-1 net (Fig. 2) has a submersible propeller that creates an entraining current of ca. 7 cm/s at the mouth of the plankton net (NXX-13, 100 m mesh). The propeller is powered by a DC-15V lithium ion rechargeable battery (8000WP-L, Daiwa). The NIPR-1 net was mounted on a sledge to facilitate direct contact with the lake bed. The mouth of the net was attached to a PVC tube containing the propeller. The tube was in turn connected to a stainless steel Wtting that narrowed to a rectangular mouth (Fig. 2) designed to improve suction eYciency at the watersediment interface. The height of the rectangular opening was adjusted to 3 cm above the sledge base. Lake Nurume Ike is a typical marine relic and meromictic lake (Sano et al. 1977). We measured the vertical proWle using a multi-water quality meter (YSI-6600, YSI) at the deepest point of the lake during the previous summer (2007) (Fig. 3). The water column consists of 3–4 layers. The surface layer (0–3 m, epilimnion) is slightly saline and is inXuenced by melt ice and water input from the surrounding catchment (Fig. 3). In contrast, the salinity of the second and third layers (3–11 m, metalimnion) is similar to the ocean. The epiand metalimnion are mixed vertically in autumn by wind-induced turbulence, thermal convection, and ice-forming processes (brine rejection and sinking). During summer oxidative conditions persist despite the development of thermal and salinity stratiWcation. The bottom layer (>11 m, hypolimnion) is completely anoxic. S. Kudoh (&) · K. T. Takahashi National Institute of Polar Research, Kaga 1-chome 9-10, Itabashi-ku, Tokyo 173-8515, Japan e-mail: skudoh@nipr.ac.jp

Microbial Communities and Their Predicted Metabolic Functions in Growth Laminae of a Unique Large Conical Mat from Lake Untersee, East Antarctica

In this study, we report the distribution of microbial taxa and their predicted metabolic functions observed in the top (U1), middle (U2), and inner (U3) decadal growth laminae of a unique large conical microbial mat from perennially ice-covered Lake Untersee of East Antarctica, using NextGen sequencing of the 16S rRNA gene and bioinformatics tools. The results showed that the U1 lamina was dominated by cyanobacteria, specifically Phormidium sp., Leptolyngbya sp., and Pseudanabaena sp. The U2 and U3 laminae had high abundances of Actinobacteria, Verrucomicrobia, Proteobacteria, and Bacteroidetes. Closely related taxa within each abundant bacterial taxon found in each lamina were further differentiated at the highest taxonomic resolution using the oligotyping method. PICRUSt analysis, which determines predicted KEGG functional categories from the gene contents and abundances among microbial communities, revealed a high number of sequences belonging to carbon fixation, energy metabolism, cyanophycin, chlorophyll, and photosynthesis proteins in the U1 lamina. The functional predictions of the microbial communities in U2 and U3 represented signal transduction, membrane transport, zinc transport and amino acid-, carbohydrate-, and arsenic- metabolisms. The Nearest Sequenced Taxon Index (NSTI) values processed through PICRUSt were 0.10, 0.13, and 0.11 for U1, U2, and U3 laminae, respectively. These values indicated a close correspondence with the reference microbial genome database, implying high confidence in the predicted metabolic functions of the microbial communities in each lamina. The distribution of microbial taxa observed in each lamina and their predicted metabolic functions provides additional insight into the complex microbial ecosystem at Lake Untersee, and lays the foundation for studies that will enhance our understanding of the mechanisms responsible for the formation of these unique mat structures and their evolutionary significance.

Abundant deposits of nutrients inside lakebeds of Antarctic oligotrophic lakes

Most freshwater lakes in continental Antarctica are in a paradoxical situation as they are in nutrient-poor conditions despite luxuriant vegetation growth covering the entire lakebed. Although the phytobenthos possibly take up nutrients from inside lakebeds, the amount of nutrients and their utilization by these phytobenthos are unclear. Sediment cores were collected from 17 freshwater lakes in East Antarctica, then dissolved inorganic nitrogen (DIN) and phosphate of the lake waters, and the vertical profiles of the interstitial water in the sediment cores were analyzed. Here we revealed that there are abundant nutrients inside lakebeds surface with 3–220 times the amount of DIN and 2–102 times concentration of phosphate than those in lake water, and the nutrient profile inside the sediment suggested that the phytobenthos can utilize the much nutrients from lakebeds. We also show that nitrogen stable isotope ratios of shallower phytobenthos lying on the small amount of nutrients in a lake are similar to that of terrestrial cyanobacteria possessing N2 fixation ability.

Possible ecological implications of floating microbial assemblages lifted from the lakebed on an Antarctic lake

Microbial assemblages can be found drifting/floating in lake water and being washed ashore in continental Antarctica. Two field studies in early and late January 2008 measured the light utilization properties and photosynthetic responses of these assemblages, which were then compared with those of pelagic and benthic microbial communities to evaluate the ecological implications of this phenomenon. The nutrient concentrations were low in the lake water, indicating oligotrophic conditions. Based on microscopic and pigment analysis, both the floating and benthic communities were mainly composed of Oedogonium sp. (Chlorophyceae), followed by cyanobacteria, diatoms, and dinoflagellates. Floating assemblages had a firmer and denser structure, and possessed more rich carotenoids than the benthic community. Measurements of photosynthesis conducted in early January indicated that the activities of the floating assemblages were considerably low. In late January almost all floating assemblages on the lakeshore turned white because of freezing and drying by the ambient temperature decrease, and had no photosynthetic signals. These results suggest that the floating assemblages could spontaneously lift off from the lakebed because of the bubbles created by photosynthesis and then repeatedly roll, flip, sink, or float depending on buoyancy. In addition, this phenomenon seemed to greatly change the cycling of matter by transporting the lake’s photosynthetic products to the surrounding ecosystems, then give the benthic subsurface communities in dark regions a chance to reactivate such as gap regeneration in the case of climax forest, and also allow the floating assemblages to restart photosynthesis at the top of the lakebed by resinking.

Abundance, richness, and succession of microfungi in relation to chemical changes in Antarctic moss profiles

Little is known in continental Antarctic about patterns of abundance, diversity, and succession of microfungi within moss profiles consisting of live, senescent, and dead tissues in different stages of decomposition. In the present study, vertical patterns of the abundance and diversity of microfungi and their relationship with chemical compositions were examined within moss colonies collected from coastal outcrops in the Lützow–Holm Bay area (Queen Maud Land), East continental Antarctica. Total and darkly pigmented hyphal length, the richness of molecular operational taxonomic units (MOTUs) of microfungi, and the occurrence of Phoma herbarum and Pseudogymnoascus pannorum increased with the depth of moss profiles. The content of organic chemical components and nitrogen in moss tissues decreased, whereas ash content increased with the depth of moss profiles. Relative amount of recalcitrant compounds and total carbohydrates did not significantly differ among the vertical layers. The downward increase of the microfungal richness and occurrence in the Antarctic moss profiles without MOTU replacement was consistent with the directional-nonreplacement model of succession, indicative of the high environmental resistance, which represents the sum of the adverse factors hindering the success of species establishment. This contrasted with the fungal succession in arctic moss profiles, which accorded with the directional-replacement model, in which species replacement took place due to modification of habitat and competition. More hostile environmental conditions than those in the Arctic characterized the fungal succession and limited the fungal decomposition of moss in continental Antarctica.