Effect of abiotic stressors (As, Cl and Pb) on rhizomicrobiome and nutrient removal in a floating Equisetum hyemale wetland

Floating Treatment Wetlands (FTW) are receiving growing interest as a phyto-technology which shows promising removal of nutrients and potentially toxic elements (PTEs) from contaminated water bodies at low operating costs. However, there are notable research gaps concerning the functions of plant species and the interactions between plants and the microbiomes residing in their roots, in the context of understanding the mechanisms for removing specific contaminants.In this study, the performance of high silicate content species Equisetum hyemale for nutrient uptake was examined in FTW microcosms under the influence of specified abiotic stressors: arsenic (As conc. 3 mg/L), lead (Pb conc. 3 mg/L) and chloride (Cl- conc. 300 and 800 mg/L) in reference to control during screening experiment (50 days, divided into 2 phases with replenishing of nutrients). Removal efficiencies of nutrients, up to 88% for TN and 93% for PO4-P were observed. However, PO4-P removal was inhibited in the As reactor at a max of 11%. Pb and As were removed with high efficiency, reaching 98% and 79% respectively. From the analysed pollutants, only Pb was substantially bound in root biomass (up to 43.7%), indicating E. hyemale as Pb bioaccumulator. This effect was most likely attributed to the high silicate content of the species. The development and structure of microbiome in microcosms were analysed by means of through 16S rRNA gene amplicon sequencing, revealing that Pb was the most influential factor in terms of selection pressure on specified bacterial groups. To a minor extent, As presented selective pressure favouring Serratia subpopulation, while Cl- treatment resulted in the rhizobiome composition most similar to control. The outcomes of this study indicate that E. hyemale is a suitable species for FTW usage in Pb and As polluted water bodies, at the same time capable to withstand periodic salinity increases. Analysis of the composition of the microbiome in the root zone of showed adaptive changes under the presence of specific micropollutants, indicating that the mechanisms responsible for their removal/neutralization in FTW systems are linked to the mutual interaction of host plant metabolism and microbial activity.