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. 0^oC, 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.