Responses of Dissimilatory Nitrate Reduction to Ammonium and Denitrification to Plant Presence, Plant Species and Species Richness in Simulated Vertical Flow Constructed Wetlands

This study investigated the effects of plant presence, plant species and their species richness on plant biomass production, pH, dissolved oxygen (DO), oxidation-reduction potential (ORP), denitrification (DNF), dissimilatory NO3 − reduction to ammonium (DNRA) and two associated bacterial community compositions in thirty vertical flow microcosm wetlands fed with the Hoagland solution, where three plant species richness levels (i.e. unvegetated, monocultured and 4-species polycultured treatment, respectively) were established using four macrophytes. Plant presence increased DO and ORP values, as well as the terminal restriction fragment (TRF) richness and Shannon-Weaver index of the DNRA community and also improved both potential DNF and DNRA rates. The microcosms monocultured with Cyperus alternifolius exhibited the greatest DO, ORP, smallest plant biomass parameters and DNF rates among all of the monocultured microcosms, whereas the microcosms monocultured with Canna glauca and Iris pseudacorus harbored the smallest pH, DO, ORP, the greatest plant biomass parameters and DNRA rates. Compared to both unvegetated and monocultured treatments, the 4-species polycultured treatment was effective in increasing both potential DNF and DNRA rates due to the greatest plant biomass parameters as confirmed by the correlation analysis, but was ineffective in terms of changing both DNF and DNRA community compositions.