Alpine constructed wetlands: A metagenomic analysis reveals microbial complementary structure

Constructed wetlands (CWs) are used to water treatment worldwide, however their application at high-altitude is poorly studied. In order to survive mountain winters, CWs rely on native flora and associated microbial communities. However, the choice of plant-microbes pairs more suitable for water treatment is challenging in alpine environments. Using a metagenomic approach, we investigated the composition of prokaryotes and fungal communities, through ex- tensive sampling inside a constructed wetland in the SW-Alps. Best performing plant species were searched among those hosting the most diverse and resilient microbial communities and to this goal, we analysed them in the natural environment also. Our results showed that microbial communities were less diverse in the CW than at natural condi- tions, and they differed from plant to plant, revealing a clear variation in taxonomic composition between forbs and gramineous plants. Carex rostrata, Deschampsia caespitosa and Rumex alpinus hosted bacteria very active in N-cycles. Moreover, fungal and prokaryotic communities associated to R. alpinus (Polygonaceae) turned to be the richest and sta- ble among the studied species. In our opinion, this species should be prioritized in CWs at high elevations, also in con- sideration of its low maintenance requirements.