Print PageMicrobial community assembly is potentially controlled by a combination of historical and contemporary processes operating over millennial to seasonal time scales. Here I present research investigating the influence of glacial history (historical legacy) and geochemical variation (contemporary environment) on the spatial distribution of soil microbes in an Antarctic polar desert. Our objective was to investigate the relative influences of historic and contemporary factors on the spatial distribution of soil microbial communities and their contribution to ecosystem processes. We collected samples in December 2010 from four different glacial till sequences in Taylor Valley, representing over 3 million year difference in soil development and predictable variations in nutrient levels and geochemistry. Within each till unit, samples were collected from either areas within the margins of melt water flowpaths or areas well outside their influence (i.e. seasonally wet or continuously dry). Using TRFLP of 16S rDNA fingerprints of microbial communities we derived community similarity and richness analyses across all sites. Extracellular enzyme activity of C-, N-, and P-acquiring enzymes (α -glucosidase and β-glucosidase, leucyl aminopeptidase, and alkaline phosphatase, respectively) provided an assessment of microbial community contribution to nutrient cycling.
Results/Conclusions
We found microbial communities were significantly influenced by both glacial tills (historical drivers) and local hydrology (contemporary driver). Community similarity was especially organized by water content, pH, phosphate, and soil organic carbon. The activity of C- and P-acquiring enzymes was more significantly influenced by glacial tills. In particular, phosphatase activity was strongly related to phosphorus content differences inherent in glacial till parent material. However, N-acquiring enzyme activity was significantly influenced instead by hydrologic condition, probably due to the increased enzyme efficiency at higher pH in dry sites. The difference among enzymes is related to edaphic soil conditions determined by either glacial history or hydrologic condition. Because the enzymes are strongly related to the geochemistry of the soil, it is unlikely that the microbial community identity influences their functional potential, indicating functional redundancy for these processes. Our work suggests that biogeography in microbial communities is co-organized by historical legacy and contemporary environments, while these functions do not appear to be dependent on community structure.
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