Simulation of seasonal changes in microbial activity of maritime antarctic peat
Seasonal variations in temperature and moisture in moss peat were monitored in the field at Signy Island, Antarctica. When simulated in intact peat cores in vitro after frozen storage, these variations caused changes on O2-uptake which closely reproduced the results for fresh samples. Respiration rate was used as a measure of aerobic decomposer activity. Supplements of sugars indicated the predominance of microbial respiration and its dependence on the availability of dissolved organic C (DOC). Low temperatures of 0° to 1°C were not rate-limiting for respiration in vivo or in vitro, and O2-uptake was detected at −1°C. Repeated peaks of O2-uptake under wet conditions resulting from simulated spring freeze-thaw cycles, and a solitary peak during an autumn simulation, suggested release of DOC substrates from frost-damaged cells. Desiccation, microfaunal predation and microaerophily were thought to contribute to respiratory declines. O2-uptake and CO2-evolution were equivalent in peat beneath Polytrichum sampled in autumn. Peat respiration was not generally proportional to microbial biomass, but saccharolytic yeasts were dominant during the respiratory maximum in spring and correlated with O2-uptake in a mixed culture of indigenous microflora. Yeasts grew exponentially in freezethaw cycle simulations but percolated into the peat profile in the field. The basal O2-uptake, which may be attributable to the decomposition of redalcitrant molecules such as cellulose, was lower in simulations of spring than autumn. Although bacterial biomass increased and diversified during summer, the ratio of fungal-to-bacterial contributions to O2-uptake in an incubated homogenate of peat sampled in autumn was 4:1.