Interactive effects of warming and species loss on model Antarctic microbial food webs

1. Predicting the effects of warming and species loss on ecosystems are two significant challenges currently facing ecologists. However, little is known of the interactive effects of these two factors. We hence tested whether or not warming and species loss interact to influence productivity and dissolved nitrogen concentrations in model Antarctic microbial food webs. Food webs, consisting of a uniform bacterial community and mixtures of six, four, two and zero bacterivorous flagellate species, drawn randomly from a pool of six flagellate species isolated from an Antarctic freshwater lake, were grown in soil extract suspension medium held in microcosms for 252 h. Half of the microcosms were kept at 4 °C and half were warmed to 8 °C over the first 36 h and then held at this temperature. 2. After 252 h there were significant interactive effects of flagellate species loss and warming on the abundance of bacterial prey and the concentration of ammonium in the medium: bacterial abundances were reduced by 75% and NH4-N concentrations were doubled in mixtures inoculated with six and four flagellate species, compared with those inoculated with two species, but only in warmed microcosms. This difference in response was apparently largely owing to the absence of Bodo saltans and Spumella putida, species with high grazing activities and growth rates, from most replicates of the warmed two species mixtures. 3. Evidence for an apparent complementarity effect was also found, with B. saltans and Spongomonas uvella growing more rapidly at 4 °C in mixtures of six species than in those of four species. 4. Data from a separate experiment, in which the flagellate species were grown in single-species culture under food-saturated conditions, confirmed that the logarithmic growth rates of B. saltans and S. putida were the highest of each of the six species at both 4 °C and 8 °C. 5. We broadly conclude from our data that random species loss from food webs or communities is likely to alter their responses to environmental change, largely owing to interspecific differences in responses to change

Solution geochemistry and behaviour of major and trace elements during summer in a moss community at Edmonson Point, Victoria Land, Antarctica

Physical and chemical characteristics and solution geochemistry of major and trace elements were investigated in an area of volcanic soil colonized by mosses at Edmonson Point (central Victoria Land) during the international BIOTAS (Biological Investigations of Terrestrial Antarctic Systems) expedition (BIOTEX) in the 1995–96 summer. The broad objective was to study the environmental factors involved in plant colonisation and survival in terrestrial continental Antarctic ecosystems. The results showed that moss distribution and survival throughout the summer was closely dependent on water supply. In Antarctic coastal ecosystems the environmental biogeochemistry is largely dominated by ions of marine origin. At the drier end of a hydrological gradient the dry cushions of Hennediella heimii were encrusted with salts and showed much higher concentrations of soluble ions (Na+, Cl−, K+, Ca2+, Mg2+, SO42−, NO3−) than those in adhering soil particles or in other moss species from wetter parts of the transect. Although salt encrustations may partly derive from sublimation of surface snow, comparisons between concentrations of soluble ions in the dry moss and those in the < 2 mm fraction of surface and deep soil showed an upward migration along the soil profile of soluble ions as the substratum dried out, between December and January, and their accumulation mostly on mosses. At the wet end of the transect messes were less affected by salt encrustations and there was evidence of Ca2+ uptake and an active cycling of nutrients

Biological and environmental characteristics of three cosmopolitan mosses dominant in continental Antarctica

Bryum argenteum, B. pseudotriquetrum and Ceratodon purpureus are the predominant mosses in Victoria Land, continental Antarctica. All have cosmopolitan distributions and are widespread throughout Antarctica with wide ecological amplitudes resulting in considerable morphological variation. They are well adapted to tolerate the physiological stresses imposed by the severe environment. This study investigates aspects of their growth, physiology and survival in response to habitat constraints, especially hydrology. Their distribution is controlled almost exclusively by moisture availability. Each species tends to predominate in a specific zone along hydrological gradients, with B. pseudotriquetrum on moist soil, C. purpureus on drier soil, and B. argenteum on unstable stream margins, fluvial deposits and the marginal capillary zone. Where conditions are optimal, each species can form a turf 6–10 cm thick. Nutrient status of the soil does not appear to be an important determinant in the distribution pattern within communities. The thermal regime of the moss turf varies according to its moisture content; for a period of ca. six weeks during the summer, with the frequent long spells of 24-h sunshine, temperatures remain above 0 °C for much of the time even though air temperatures are frequently below the freezing point. This allows growth and metabolic activity to proceed continuously at a relatively rapid rate for quite long periods. Annual shoot incremental growth can exceed 3.5 mm in each species. Growth of B. argenteum may be inhibited by UV- B radiation. The optimal temperature for photosynthesis in each species is around 15 °C, but significant carbon fixation occurs at 5 °C. Photosynthetic rates at 5, 10 and 20 °C were B. argenteum > B. pseudotriquetrum > C. purpureus

Species diversity and resource relationships of South Georgian fungi

The occurrence and distribution of the South Georgia fungal flora, particularly Ascomycotina and Basidiomycotina, is assessed in terms of habitat and substrate preference. The 113 taxa reported comprise 37 basidiomycetes, 49 ascomycetes, six myxomycetes and at least 21 lower fungi. Peat and litter substrata associated with tall tussock grassland have a rich macro-fungal flora, and numerous species occur in bog and mire communities, some in abundance from mid to late summer. Many micro-fungi and ascomycetes colonize dying leaves and inflorescences of specific vascular plants, and a few colonize bryophytes and lichens. At least a dozen species, probably non-indigenous, are associated with rotting timber and other imported materials at former whaling stations. An intensive survey of the South Georgia mycoflora is necessary to gain better understanding of their role in decomposition and nutrient cycling processes in the principal plant communities

Plants of extreme habitats in Antarctica

An account is given of phanerogams and cryptogams(bryophytes and lichens) growing in extreme habitats in Antarctica. These include high altitude and far southern sites, geothermal sites in volcanic areas, and deep water habitats, all of which confer considerable physiological stress on these organisms and represent the limits of non-microbial life in this biome and, to a large extent, on planet Earth