Shifts in bacterial and fungal community structure and functional potential along a boreal forest successional gradient

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What drives microbial community structure and function is a fundamental question in microbial ecology.  Many studies have found that and plant successional stage and soil environmental factors affect the soil microbial community, and advances in molecular tools enable more in-depth analyses that may facilitate deeper understanding and predictive potential regarding shifts in microbial diversity and function as landscapes change. We used bar-coded pyrosequencing of bacterial 16S rRNA genes, Sanger sequencing of the fungal internal transcribed spacer (ITS1-F), and GeoChip functional gene microarray analyses to screen the total microbial structural and functional potential of organic horizon soils associated with forest stands representing a successional gradient the Bonanza Creek Long Term Ecological Research Site (BNZ LTER) in interior Alaska.  Early to mid-succession tree stands were dominated by Populus tremuloides (quaking aspen), or Betula neoalaskana (Alaskan paper birch), and late successional stages tree stands were dominated by either Picea glauca (white spruce) or Picea mariana (black spruce). Our results indicate that differences in both bacterial and fungal community structure are driven by the dominant vegetation type and therefore successional stage. Additionally, there is a strong relationship between the measured bacterial and fungal communities suggesting that the communities co-vary along the measured successional gradient.  Successional effects were also observed in the functional genetic profiles, and distinct arrays of genes associated with complex carbon cycling varied in association with the four investigated tree stand types. Overall, these data provide a high resolution profile of the linkages between microbial and vegetative communities, and suggest that any changes in the vegetative community could cause associated shifts in soil microbial community structure and function, particularly with respect to carbon cycling.