Louis Beyens

Testate amoebae populations from moss and lichen habitats in the Arctic

SummaryForty-five taxa of testate amoebae were found in 53 samples from mosses and lichens collected in East Greenland (Angmagssalik region), Jan Mayen and N.W. Spitsbergen. It is possible to distinguish four associations, with a different responses in relation to the moisture content, the hydrogen-ion concentration and the increasing continentality with latitude. A trend of diminishing diversity and number of taxa towards the north is also shown.

Climate Warming Postpones Senescence in High Arctic Tundra

Abstract Lengthening of the growing season at high latitudes, observed by satellites with the Normalized Difference Vegetation Index (NDVI), has been ascribed to climate warming. To test this assumption, and to verify whether changes in vegetation greenness are quantitative or qualitative, we experimentally warmed patches of High Arctic tundra with infrared heating in Northeast Greenland. By analyzing digital images of the vegetation, changes in cover were distinguished from changes in senescence. During the season, experimental warming significantly increased green cover, for example, at the time of peak cover, the total green cover was enhanced from 59.1 to 67.3%. The dominant wavelength (hue) reflected by our tundra plots shifted from yellow-green to yellow. Experimental warming with 2.5°C delayed this hue-shift by 15 d. The results demonstrate that higher summer temperatures do not only promote plant growth at these latitudes but also retard and/or postpone the senescence process, contrary to indications from previous research that late-season phenology in the High Arctic is governed by photoperiod.

The epiphytic diatom flora of mosses from Strømness Bay area, South Georgia

Abstract A total of 104 taxa, belonging to 27 genera, were recorded from 36 moss samples collected in the Strømness Bay area. Cluster analysis revealed two groups of samples. Group 1 consisted of the Achnanthes incognita–Fragilaria germainii assemblage and the Eunotia paludosa var. paludosa assemblage. Group 2 included the Pinnularia borealis assemblage. The major ecological factor dividing the two groups appears to be the moisture content of the samples. Group 1 represents wetter conditions, and the second group is found on very dry mosses. The assemblages of group 1 were separated from each other by pH. The Achnanthes incognita–Fragilaria germainii assemblage occurs in wet mosses with a circumneutral pH. The Eunotia paludosa var. paludosa assemblage prefers bryophyte habitats with low pH values. The size of Pinnularia borealis drops significantly according to the dryness of the moss habitat.

An Annotated List of Testate Amoebae Observed in the Arctic between the Longitudes 27° E and 168° W

Summary A geographic database is presented of the occurrence of the 220 testate amoebae taxa observed by the authors in the Arctic between the longitudes 27°E and 168°W. Visited and studied were localities in Svalbard (West Spitsbergen, Edgeoya, Barentsoya, Hopen, Bear Island), Jan Mayen, Greenland (Angmagssallik and Sondre Stromfjord region), Canada (Devon Island, Victoria Island), and Alaska (Barrow and Nome regions). The number of samples analysed was 1142. For each region, information is given on the occurrence of the taxa in different habitats. Browsing the data from other authors completes this protistological list with 71 taxa not seen by us, resulting thus in a total of 291 testate amoebae taxa known from the Arctic.

Moss-inhabiting diatom communities from Heard Island, sub-Antarctic

In this paper, we list 192 diatom taxa, collected from bryophyte samples from Heard Island (52°05′S, 73°30′E). The Heard Island diatom flora shows a marked similarity to those of the Crozet and Kerguelen archipelagos, and is quite dissimilar to the moss-dwelling diatom flora of Macquarie and Amsterdam Island. Based on species composition, three main groups of samples could be discerned. Each group represents a different habitat. Samples dominated by Diadesmis ingeae, Pinnularia borealis and several Psammothidium species seem to prefer the driest habitats. A special form of this community was found in shaded areas. Samples from wet habitats such as flush areas and pools were dominated by species such as Adlafia bryophila, Sellaphora tumida, Fragilaria capucina and Planothidium lanceolatum. An intermediate group was observed in more acid, but terrestrial, conditions, characterised by Eunotia paludosa and Chamaepinnularia soehrensis var. muscicola. These community patterns are similar to those found on other sub-Antarctic islands, and we suggest that a group of typical sub-Antarctic species and communities exists.

Increased Turnover but Little Change in the Carbon Balance of High-Arctic Tundra Exposed to Whole Growing Season Warming

Abstract Tundra ecosystems constitute large stocks of carbon and might therefore, if climate warming releases CO2, induce positive feedback and amplify temperature increase. We studied the effect of a 2.5°C temperature increment, induced by controlled infrared irradiation, on various components of the carbon balance of a High Arctic tundra ecosystem at Zackenberg in Northeast Greenland (74°N, 21°W) over the 1999 growing season. Gross photosynthesis (Pgross), belowground respiration (Rsoil), and canopy respiration (Rcanopy) were regularly determined with closed dynamic CO2 exchange systems, and the whole-growing season C-balance was reconstructed by relating these components to potentially controlling factors (green cover, soil moisture, radiation, soil and canopy temperature, and thawing depth). Thawing depth and green cover increased in heated plots, while soil moisture was not significantly affected. Pgross increased 24.2%, owing to both a green cover and a physiological influence of warming. Belowground respiration was enhanced 33.3%, mainly through direct warming impact and in spite of lower Q10 in the heated plots; the factors controlling Rsoil were day of the year and soil moisture. Rcanopy did not differ significantly between treatments, although green cover was higher in the heated plots. This tundra ecosystem acted as a relatively small net sink both under current (0.86 mol CO2 m−2) and heated (1.24 mol CO2 m−2) conditions. Nevertheless, turnover increased, which was best explained by a combination of direct and indirect temperature effects, and delayed senescence.

Habitat preferences in freshwater diatom communities from sub-Antarctic Îles Kerguelen

A limited sampling campaign on the main island of Îles Kerguelen revealed 170 freshwater diatom taxa, belonging to 29 genera. Four different communities were distinguished in two major groups, being determined principally by habitat type. The Fragilaria vaucheriae–Fragilaria germainii assemblage occurs exclusively in running waters. The three other communities, observed in standing waterbodies, are separated by their geographical position on the island with the Fragilaria exigua–Aulacoseira alpigena and the Fragilaria exigua–Fragilaria vaucheriae assemblages, mainly found in the Lac Studer area and the Fragilaria pinnata var. pinnata assemblage, recorded near the coastal line and the research station. Analysis of different waterbody types revealed the habitat preference of the various diatom taxa and identified a diatom flora for running waters and one preferring stagnant waterbodies.

The aquatic testate amoebae fauna of the Strømness Bay area, South Georgia

Forty six taxa of testate amoebae were found in 45 samples of aquatic environments ranging from small pools to lakes. Four assemblages were distinguished which, to some degree, can be related ecologically to different pH ranges, and to differences in the habitat structure. The Nebela collaris assemblage occurs in acid pools mostly vegetated with mosses. The Centropyxis gibba gibbosa–Euglypha tuberculata–Difflugia globularis/globulus assemblage is found in the sediments of circumneutral to slightly alkaline lakes. Both of the other assemblages are mainly found in pools, which are more (for the Trinema assemblage) or less vegetated with mosses, in slightly acid (the Difflugia penardi–Centropyxis aerophila assemblage) or circumneutral to slightly alkaline (the Trinema lineare assemblage) conditions. A generic comparison with the Arctic fauna indicates differences, especially in the role of Difflugia as a dominant genus in aquatic habitats.

Ecology of terrestrial testate amoebae assemblages from coastal Lowlands on Devon Island (NWT, Canadian Arctic)

SummaryFifty-seven taxa belonging to 17 genera of testate rhizopods were recorded in samples of mosses, soils and lichens, collected from the Truelove and Sparbo Hardy Lowlands on the high arctic Devon Island (NWT, Canada). Different groups of habitats are characterized by particular assemblages of Testacea species, with the quantity and quality of the available water as important ecological parameters. The Assulina muscorum-Corythion dubium assemblage characterizes the most dry and acidic moss habitats, while the Paraquadrula irregularis assemblage is to be found in wet and rather neutral habitats. The sedge moss meadows with their more moderately coarse textured and poorly drained soils, bear a Plagiopyxis callida-Plagiopyxis declivis soil-dwelling testate amoebae assemblage. The Centropyxis minuta assemblage lives in the most coarsely textured soils. pH seems to play a subordinate role, not only in the mosses but also in the soils. Multivariate methods (cluster analysis and CANOCO) have been used to separate these different assemblages.

Plant Functional Group Diversity Promotes Soil Protist Diversity

We tested whether effects of plant diversity can propagate through food webs, down to heterotrophic protists not linked directly to plants. To this end we synthesised grassland ecosystems with varying numbers of plant functional groups (FGN) and assessed corresponding changes in testate amoebae communities. The number of plant species was kept constant. When FGN was increased from 1 to 3, species number and total community density of live testate amoebae were enhanced according to a linear and a saturating function, respectively. From FGN 1 to 2, the appearance of new testate amoebae species did not affect the presence of the resident species, whereas, from FGN 2 to 3 about one quarter of the resident testate amoebae species was replaced, without altering the total species number. Overall, density by species increased, while evenness of the testate amoebae community was not affected by FGN; although Trinema lineare, one of the most common species, became more abundant. The observed relationship between plant functional group diversity and testate amoebae diversity could shed new light on the biogeographical distribution patterns of protists.