PS 15-149 - The Influence of Permafrost Soil Structure on Microbial Communities

Background/Question/Methods

Soil pore and aggregate structure is increasingly recognized for its significant role in shaping soil microbial communities and biogeochemical cycling. However, although well-studied in temperate systems the importance of physical structure on soil microbial community diversity, function, and overall activity in intact permafrost soils is largely unknown. Soil structure in permafrost is likely to be important in shaping microbial communities because of its influence on the availability and distribution of unfrozen water. Microbial activity requires unfrozen water which can primarily be found surrounding ice inclusions and soil pores. We hypothesize that in permafrost with greater ice inclusion and pore surface area, which results in more habitable space, the abundance and diversity of the active microbial community will increase. We analyzed 8 permafrost cores from three distinct sites in Alaska. Cores were subsampled in triplicate to capture fine scale heterogeneity soil physical and biological characteristics. To quantify soil ice inclusion and pore architecture we utilized X-ray Computed Tomography, scanning permafrost at -10 ºC to maintain structure. Following scanning, both DNA and RNA were extracted from the permafrost and analyzed via amplicon sequencing and quantitative PCR of the 16S region. We analyzed the total and active microbial community composition, diversity, and abundance.

Results/Conclusions

Microbial community alpha diversity increased significantly in sites with lower carbon and nitrogen content. These results may signify nutrient poor conditions push communities towards a more diverse set of survival strategies. Also, we found that the diversity between RNA and DNA communities was very similar within samples, but the composition of the RNA communities was dominated by several different phylum. Identifying the active community in permafrost may give insight to the development of the community when faced with disturbance events associated with climate change. Soil physical structure as measured through volumetric composition of pore space, ice, and soil as well as ice inclusion and pore surface area, connectivity, and size distribution were not significantly related to the microbial community diversity, abundance, or activity. However, soil structure within and between sites exhibited significant differences in composition and porosity. These results indicate structure may not be a key factor shaping microbial communities or that our ability to measure these interactions is hindered by the limited resolution of both structural and microbial data.