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Long-Term Research in Environmental Biology: What controls long-term changes in freshwater microbial community composition?
(NSF-DEB 0639790)
PIs: Byron C. Crump, George W. Kling
 


Microbial ecology came to the forefront of biological and ecological science in the 1990s with the development of high-throughput DNA sequencing and other molecular techniques.  Recently this field entered a second age of understanding that microbial diversity was organized into patterns at various scales, consistent with ecological concepts that were once thought applicable only to macro-organisms.  Evidence of these patterns in diversity contradicts the traditional microbial hypothesis from Bass-Becking (1934) that “Everything is everywhere, but the environment selects,” and indicates that, as with larger organisms, dispersal processes influence microbial diversity even at regional and local scales.  It is clear that both dispersal and environmental conditions are related to patterns of diversity (Figure 1), but to date the mechanistic controls and the relative importance of these factors have not been determined.


Fig. 1. Conceptual diagram of general controls on microbial community composition

The goal of this research project is to resolve these controls through a combination of field and lab experiments with monitoring and surveys of the phylogenetic composition and ecosystem function (metabolism) of microbial communities.  This work builds on a six-year record showing consistent spatial and temporal patterns of microbial growth and community composition in ~25 lakes and streams of the Toolik Lake Research Area in Arctic Alaska.  Using experiments coupled with established sampling protocols and routines (leveraging the Arctic Long Term Ecological Research (http://ecosystems.mbl.edu/ARC/) monitoring program), this research will answer 3 basic questions, and focus on the long-term aspects of dispersal events and climate change:
1.  How does environment influence microbial community composition and rate of function?
2.  How are distribution patterns of microbial communities in lakes, streams, and soils influenced by dispersal via down-slope water flow?
3.  How are seasonal, inter-annual, and long-term shifts in microbial community composition related to temporal shifts in environmental conditions such as those caused by climate change?
Long-term investigations of microbial communities are critical for understanding patterns of diversity and their controls, especially because the most enduring dispersal events are also most rare.  Moreover, because this work is located in the Arctic it will capture the earliest biological effects of global climate change. The Toolik Research Area (http://www.uaf.edu/toolik/) (Figure 2) is ideal for this because climate change has yet to affect environmental conditions critical for microbe dispersal and function (e.g., hydrology), and thus the current 6-year dataset establishes a baseline condition.  Also, and perhaps most important, molecular technology for analyzing microbial communities is advancing rapidly, and a cohesive, long-term archive of DNA samples and associated environmental information will be extremely valuable in the future for application of these new analyses.

Fig. 2. Maps of Toolik Lake and the surrounding region including (A) a map of the Toolik Lake catchment with lake and stream sampling sites indicated, (B) A diagram of lakes in the Toolik catchment, (C) a map of lakes and streams that have been sampled by the Arctic LTER program (samples lakes are numbered), (D) a bathymetric map of Toolik Lake, and (E) a map of Alaska indicating the location of Toolik Field Station.