The overall goal of our DOE-supported project is to advance system-level predictive understanding of the feedbacks of belowground microbial communities to multiple climate change factors and their impacts on soil carbon cycling processes. In particular, we are experimentally heating, in-situ, 2 to 4 °C above ambient temperature two sites, an Alaskan tundra permafrost (AK) and an Oklahoma temperate grassland (OK). By coupling respiration data and soil indices with well-replicated whole-community shotgun metagenomic sequencing from control and warming plots we hope to improve our understanding of: i) the indigenous microbial communities and their functions in these two important ecosystems for climate, ii) microbial biogeographic patterns across large regions spanning several hundred kilometers, and iii) the microbiological basis underlying temperature sensitivity of soil organic matter decomposition. To enable this research, we have been also developing bioinformatics tools for metagenome analysis and comparison as well as for data integration, and we have been making these tools available for online analysis or download for standalone applications through a dedicated webserver (http://enve-omics.ce.gatech.edu/).
Results/Conclusions
Metagenomes collected after 1 and 5 years of warming yielded near-complete representation of microbial community ‘sequence richness’ at AK and OK sites, and revealed that AK communities are ~10 times less diverse. A custom-made assembly and contig binning strategy allowed for the recovery of many near-complete bacterial population genomes from both locations. In particular, populations recovered from AK soils collectively made up to ~15% of the total microbial community. These genomes represented diverse taxonomic groups and metabolic lifestyles tuned toward sulfur cycling, hydrogen metabolism, methanotrophy, and organic matter oxidation. While the 1-year data revealed small shifts in pathways related to SOM-decomposition, the 5-year data showed dominant bacterial populations shifting in abundance by as much as 80% in response to the warming treatment. Therefore, even such mild warming conditions induce detectable changes in microbial communities and these changes mediate feedback responses. Further, several bacterial populations recovered from AK tundra soils were present and dominant in geographically distant (~100-530 kilometers apart) tundra habitats (>98% genome-derived average nucleotide identity) but not in OK samples. Therefore, their relative contribution to various ecosystem functions is expected to be high and their individual responses to climate warming may be of significance to large geographic regions.