Bacterial diversity and community structure in native legume root nodules in intact and mining disturbed tundra

Background/Question/Methods

Mining activity causes major disruptions to the balance of an ecosystem and in tundra environments, results in large areas of bare substrate that are very slowly colonized by vascular plants. In these disturbed soils, the initial colonizing vascular plants likely play an important role in adding organic material and stimulating microbial activity. Exposed gravel pits at the Meliadine gold mine in Nunavut, Canada are colonized by three species of native legumes. These legumes, with their ability to fix atmospheric nitrogen, may drive the establishment and succession of secondary colonizers through the deposition of critical carbon and nitrogen resources via the rhizosphere microbiome. Here we examine the Rhizobium communities in root nodules from native Oxytropis, Astragalus, and Hedysarum genera colonizing disturbed gravel and in intact tundra. 16S and nifH amplicons from nodule occupant DNA were sequenced using Miseq Illumina sequencing and the sequence information obtained were compared to known sequences to characterize and compare the bacterial diversity between the different legume species.

Results/Conclusions

Gravel pit soils were rocky with little organic material, rapid drainage, and greater depth of the permafrost layer compared to intact tundra collection sites. Oxytropis arctica and Astragalus alpinus were frequently encountered both on the gravel pits and intact tundra, while O. maydelliana was less often found on gravel pits and Hedysarum alpinum rarely so. Rhizobia composition diversity was compared between the four species and between gravel pit and intact tundra areas. Understanding the adaptations that make Oxytropis arctica and Astragalus alpinus earlier colonizers of disturbed mining areas is critical to make recommendations for the restoration of ecosystem function after mine closure.