Contrasting Water Quality Treatments Result in Structural and Functional Changes to Wetland Plant-Associated Microbial Communities in Lab-Scale Mesocosms.

The impact of contrasting water quality treatments on wetland plant-associated microbial communities was investigated in this study using 12 lab-scale wetland mesocosms (subsurface flow design) planted with reed canary grass (Phalaris arundinacea) or water speedwell (Veronica anagallis-aquatica) over a 13-week period. Mesocosms received water collected from two sites along the Grand River (Ontario, Canada) designated as having either high or poor water quality according to Grand River Conservation Authority classifications. All mesocosms were established using sediment collected from the high water quality site and received water from this source pre-treatment. Resulting changes to microbial community structure were assessed using PCR-denaturing gel gradient electrophoresis (DGGE) on microbial 16S rDNA sequences extracted from rhizoplane, rhizosphere, and water samples before and after exposure to water quality treatments. Functional community changes were determined using Biolog™ EcoPlates which assess community-level carbon source utilization profiles. Wetland mesocosm removal of inorganic nutrients (N, P) and fecal coliforms was also determined, and compared among treatments. Treatment-specific effects were assessed using a repeated measures restricted maximum likelihood (REML) analysis. Structural and functional characteristics of rhizoplane microbial communities were significantly influenced by the interaction between plant species and water treatment (P = 0.04, P = 0.01). Plant species-specific effects were observed for rhizosphere structural diversity (P = 0.01) and wetland water community metabolic diversity (P = 0.03). The effect of water treatment alone was significant for structural diversity measurements in wetland water communities (P = 0.03). The effect of plant species, water quality treatment, and the interaction between the two is dependent on the microhabitat type (rhizoplane, rhizosphere, or water). Rhizoplane communities appear to be more sensitive to water quality-specific environmental changes and may be a good candidate for microbial community-based monitoring of wetland ecosystems.