Possible ecological implications of floating microbial assemblages lifted from the lakebed on an Antarctic lake

摘要

Microbial assemblages can be found drifting/ floating in lake water and being washed ashore in continental Antarctica. Two field studies in early and late January 2008 measured the light utilization properties and photosynthetic responses of these assemblages, which were then compared with those of pelagic and benthic microbial communities to evaluate the ecological implications of this phenomenon. The nutrient concentrations were low in the lake water, indicating oligo-trophic conditions. Based on microscopic and pigment analysis, both the floating and benthic communities were mainly composed of Oedogonium sp. (Chlorophyceae), followed by cyanobacteria, diatoms, and dinoflagellates. Floating assemblages had a firmer and denser structure, and possessed more rich carotenoids than the benthic community. Measurements of photosynthesis conducted in early January indicated that the activities of the floating assemblages were considerably low. In late January almost all floating assemblages on the lakeshore turned white because of freezing and drying by the ambient temperature decrease, and had no photosynthetic signals. These results suggest that the floating assemblages could spontaneously lift off from the lakebed because of the bubbles created by photosynthesis and then repeatedly roll, flip, sink, or float depending on buoyancy. In addition, this phenomenon seemed to greatly change the cycling of matter by transporting the lake's photosynthetic products to the surrounding ecosystems, then give the benthic subsurface communities in dark regions a chance to reactivate such as gap regeneration in the case of climax forest, and also allow the floating assemblages to restart photosynthesis at the top of the lakebed by resinking.