Root-associated bacteria community characteristics of two Antarctic plants - Deschampsia antarctica and Colobanthus quitensis

Colobanthus quitensis and Deschampsia antarctica are the only angiosperms to naturally colonize the Antarctic region. The reason for their sole presence in Antarctica is still debated as there is no definitive consensus on how only two unrelated flowering plants managed to establish a breeding population in this part of the World. In this study, we have explored and compared the rhizosphere and root-endosphere dwelling microbial community of C. quitensis and D. antarctica specimens sampled in maritime Antarctica from sites displaying contrasting edaphic characteristics. Bacterial phylogenetic diversity (high throughput 16S rRNA gene fragment targeted sequencing) and microbial metabolic activity (Biolog Ecoplates) with a geochemical soil background were assessed. Gathered data showed that the microbiome of C. quitensis root system was mostly sitedependent, displaying different characteristics in each of the examined locations. This plant tolerated an active bacterial community only in severe conditions (salt stress, nutrient depravation) while in other, more favorable circumstances it restricted microbial activity, with a possibility of microbivory-based nutrient acquisition. The microbial communities of D. antarctica showed a high degree of similarity between samples within a particular rhizocompartment. The grass endosphere was significantly enriched in plant beneficial taxa of the family Rhizobiaceae, which displayed obligatory endophyte characteristics, suggesting that at least part of this community is transmitted vertically. Ultimately, the ecological success of C. quitensis and D. antarctica in Antarctica might be largely attributed to their associations and management of root-associated microbiota.