S44: Long-term elevated CO2 decreases microbial biodiversity in a grassland ecosystem as revealed by metagenomics sequencing

Understanding the responses of biological communities to elevated CO₂ (eCO₂) is a central issue in ecology and global change biology, but little is known about the impacts of eCO₂ on the function, structure, and diversity of the below ground microbial community. In this study, 24 soil samples (ambient CO2 (aCO2) vs. eCO2, all with 16 plant species) were collected from BioCON experimental site located at the University of Minnesota. Both 454 and Illumina-based metagenomics sequencing were performed, resulting in a total of ~120GB sequence data.  Annotation information showed that the majority of the gene content in soil microbial communities is novel and rare. DCA analysis showed aCO₂ and eCO₂ samples can be separated clearly, indicating eCO₂ has altered the overall functional structure of grassland microbial communities.  The core and pan functional genes were also analyzed, and results indicated that aCO₂ samples retained a broader gene content than eCO₂ samples. Further analysis showed lower functional gene diversity was observed in eCO₂ samples,  suggesting eCO₂ has potentially decreased the function diversity of microbial communities in grassland soil. Functional genes were extracted and analyzed phylogenetically. As results, the majority of functional genes studied showed decreased taxonomy diversity in response to eCO₂. Additional amplicon sequencing of several genes including 16S rRNA, nifH, and amoA also verified the results.  In conclusion, our results indicated that the overall functional and taxonomic diversity of the microbial community in grassland decreased in response to long-term eCO₂, though exceptions could be observed for some functional genes and fungi.