To evaluate the relative influences of environmental heterogeneity such as plant species and abiotic factors, I characterized bacterial community compositions in rhizosphere soil collected from Canadian and Norwegian arctic ecosystems. To elucidate the impacts of abiotic factors and plant species on rhizosphere bacterial communities, I compared rhizosphere bacterial communities on Salix polaris and Saxifraga oppsitifolia in Svalbard, Norway. In addition, to identify the influences of abiotic factors on compositions of bacterial communities in the rhizosphere, I analyzed soil bacterial communities from the rhizosphere of Dryas integrilfolia in a setting of factorial treatment of warming and adding water in Cambridge bay, Canada.
Soil bacterial community structure was studied using both next generation sequencing (NGS) and terminal restriction fragment length polymorphism (T-RFLP) with 16S ribosomal RNA (rRNA) coding genes. I conducted partial least squares discriminant analysis (PLS-DA) to select important genera associated with each samples and performed Canonical Correspondence Analysis (CCA) to analyze relationships between soil properties and rhizosphere bacterial communities.
In the glacial retreat area study in Svalbard, T-RFLP profiles and NGS sequences from S. polaris samples were clearly separated from those of S. oppsitifolia samples in PLS-DA plots. I found that Spingobium and Sphingomonas were detected in rhizosphere samples from S. polaris while Pseudomonas, Pseudonocardia and Spartobateria were largely observed in rhizosphere samples from S. oppsitifolia.
In a warming and adding watering study using open-top chambers in Cambridge Bay, rhizosphere bacterial community structures appeared to be significantly dependent on soil temperature. Additionally, I found that Geminicoccus, Sphingomonas and Ilumatobacter occurred in the D. integrifoila samples with high soil temperature, while Acidobacteria_Gp17, Pseudomonas and Pedomicrobium were largely detected in those with low soil temperature.
In conclusion, my results show that soil temperature was an important factor in determining rhizosphere bacterial community compositions in Canadian and Norwegian arctic and Ilumatobacter was one of potentially useful marker genera for increase of rhizosphere soil temperature. In the further study, characterization of not only rhizosphere bacterial community but also fungi and nematode community structure were required to investigate whole responses of soil microbial communities.
