Seasonal fluctuations in microbial activity in Antarctic moss peat

The Signy Island terrestrial reference sites epitomize unpolluted maritime Antarctic tundra. The extreme transition from the harsh Antarctic winter to the milder summer facilitates studies of the effects of freeze-thaw cycles on microbial activity in moss peat. Seasonal monitoring of peat oxygen uptake showed a transient spring peak at c. 0oC, attributed to microbial utilization of dissolved organic carbon (DOC). After a more gradual temperature-linked summer increase, autumnal freeze-thaw cycles stimulated a final pre-winter peak. The transient climaxes were associated with blooms of saccharolytic yeasts and microfungi. The bacterial population stabilized after a spring increase but then diversified as DOC became rate-limiting. Effects of pre-monitored spring freeze-thaw cycles on late-winter peat cores were simulated in a Gilson respirometer. In vitro perturbations demonstrated the regulatory effects of DOC availability, water content and temperature on peat respiration and microflora! composition. Comparative respirometry and loss in tensile strength of interred cotton strips showed a difference in decomposer activity beneath a relatively dry Polytrichum-Chorisodontium turf and a wet Cattiergon-Cephalozielta carpet. This was associated with water content and anaerobiosis. Cellulolysis accelerated during the growing season and increased with depth, despite anaerobic conditions. Estimates of annual bryophyte decomposition are presented for use in an Antarctic ecosystem model

Response of pioneer soil microalgal colonists to environmental change in Antarctica

There is increasing evidence of climate change in Antarctica, especially elevated temperature and ultraviolet B (UVB) flux within the ozone “hole.” Its origins are debatable, but the effects on ice recession, water availability, and summer growth conditions are demonstrable. Light-dependent, temperature-sensitive, fast-growing organisms respond to these physical and biogeographical changes. Microalgae (cyanobacteria and eukaryotic algae), which are pioneer colonists of Antarctic mineral fellfield soils, are therefore highly suitable biological indicators of such changes. In frost-heaved soil polygons containing naturally sorted fine mineral particles, microalgal growth is restricted to a shallow zone of light penetration. By virtue of this light requirement, microalgae are exposed to extreme seasonal fluctuations in temperature (air and black-body radiation), photosynthetically active radiation, UV radiation, and desiccation. Dominance of conspicuous autofluorescent indicator species with distinctive morphology allowed quantification of responses using epifluorescence microscopy, and image analysis of undisturbed, unstained communities. However, the physical changes in climate, although significant in the long term, are gradual. The changes were therefore amplified experimentally by enclosing the communities at a fellfield site on Signy Island, maritime Antarctica, in cloches (small greenhouses). These were made of polystyrene of either UV transparent or UV opaque acrylic plastic, with or without walls. During a 6-year period, statistically significant changes were observed in microalgal colonization of the soil surface and in the morphology of filamentous populations. Evidence of community succession correlated with measured changes in local environment was found. Results from Signy Island and at continental sites on Alexander Island suggested that rates of microalgal colonization and community development might change significantly during current climate changes in Antarctica