Arrival order affects microbial community composition in Antarctic cryoconite holes

Pacifica Sommers and Steven K. Schmidt, Ecology and Evolutionary Biology, University of Colorado, Boulder, CO, Dorota L. Porazinska, Entomology and Nematology, University of Florida, Gainesville, FL, Adam J. Solon and Lara Vimercati, Ecology and Evolutionary Biology, University of Colorado Boulder, Boulder, CO, Julian M. Cross, Department of Geography, Portland State University, Portland, OR, Kaelin Cawley, NEON, Andrew G. Fountain, Departments of Geology and Geography, Portland State University, Portland, OR

Background/Question/Methods
How much the order in which species arrive in a new habitat influences community composition has long been debated in ecology. This debate has recently been rekindled with respect to microbial ecology in particular. Satisfactory systems in which to address this question, however, are limited. Antarctic cryoconite holes provide tractable microbial ecosystems with defined boundaries and relative isolation in which to test the relative importance of arrival order. These shallow melt-holes in the top half-meter of glacial ice are formed when sediments are blown onto the ice surface and absorb solar radiation and melt the ice below them. Cryoconite holes form an oasis of liquid water for microbial growth in a polar desert that can persist for a decade or more with an icy lid preventing secondary immigration. To test the importance of arrival order, we established experimental cryoconite holes on Canada Glacier, Antarctica, and inoculated them with one of two microbial mats from nearby streams (“orange mat” or “black mat”), dominated by different organisms. After ten days of melt, we introduced the other mat. We returned one year later to collect sediment, extract DNA, and characterize the communities of bacteria and microbial eukaryotes.
Results/Conclusions
Communities in which the black mat invaded the orange mat differed significantly in their bacterial composition from those in which the orange mat invaded the black mat. Even under harsh environmental conditions in which abiotic factors are thought to exert strong deterministic control over microbial community assembly, stochastic factors such as the order of arrival appears to play a role in determining microbial community composition.