The Interaction of Soil and Lake Microflora at Signy Island

Summary

Lakes on Signy are small and, during the summer ice-free period, receive a substantial influx of run-off from the surrounding catchment, greatly in excess of their total volume. Within the various habitats comprising each lake’s catchment area, large populations of bacteria, yeasts and fungi exist. Transport of terrestrial micro-flora to the lakes in run-off water is demonstrated by the appearance of Chromobacterium and yeasts in lake surface waters at around the same time as their numbers increase in certain terrestrial habitats. However, close examination reveals substantial differences between lake and terrestrial populations, possibly the most obvious being the virtual absence of gram-positive bacteria from lake samples whilst comprising 20% of terrestrial populations. By means of numerical profiles, it has been possible to demonstrate that the composition of lake populations differs between lakes, and between lakes and their catchment populations. These differences can be explained in terms of catchment composition and nutrient availability. A study of temperature-specific growth rate characteristics indicates that successful freshwater bacteria can, in broad terms, be considered psychrophiles, whereas successful terrestrial bacteria are more psychrotolerant. A comparison of substrate affinity values indicates that freshwater bacteria are more efficient than terrestrial bacteria or yeasts in utilizing low concentrations of dissolved organic C at low temperatures. At higher temperatures, substrate affinity values are more equivalent. From the data presented, it is proposed that the two populations may be considered as a mixed-culture chemostat population. At high nutrient concentrations, a typical terrestrial population will exist and with fluctuations in temperature and nutrient level, a typical succession will also occur. But when nutrient levels drop suddenly for an extended period and temperature stabilizes at about 0 °C, a typical freshwater population emerges whose components had previously existed only in very low numbers.