Metagenomic Insights of the Feedback Responses of Soil Microbial Communities to Elevated CO2.

Understanding the responses and mechanisms of biological communities to elevated atmosphere carbon dioxide (eCO₂) is a central issue in ecology and for society.  Although the fertilization effects of eCO₂ on aboveground plants are well documented, its influences on belowground microbial communities are poorly understood. The responses of belowground microbial communities to eCO₂ will critically influence whether and how much the fertilization effects will lead to C loss or sequestration in terrestrial ecosystems. We used high throughput metagenomics technologies, such as GeoChip and pyrosequencing, to address the following questions: (i) Does elevated [CO₂] affect the composition of soil microbial communities? (ii) Does elevated [CO₂] affect soil microbial functional genes likely to influence carbon and nitrogen cycles under elevated CO₂?   Our results show that eCO₂ significantly altered the genetic and functional structure of the belowground microbial community in a grassland ecosystem in eastern Minnesota after 10 years of field exposure to eCO₂. Soil community responses are consistent with and help explain ecosystem responses involving soil carbon and nitrogen content and plant productivity. Specifically, while the functional genes involved in degrading labile carbon are significantly increased under eCO₂, the genes for decomposing recalcitrant carbon remain unchanged. The genes involved in fixing carbon and nitrogen and releasing phosphorus are also significantly increased. The results suggest that elevated [CO₂] has significant impacts on relative abundance, composition and potential functions of soil microbial communities, and they could have important implications for the feedback responses of ecosystems to atmospheric CO₂ and hence to the global climate change modeling needed for reliable prediction of future atmospheric CO2.