The water hyacinth, Eichhornia crassipes, is widely used for the ecological restoration of eutrophic freshwater bodies, but little is known about its microbial interactions and nitrogen removal potential. In this study, we compared the relative importance of E. crassipes and bacteria in nitrogen removal. We also examined the plant's ability to modulate the abundance and diversity of nitrifying and denitrifying bacteria. Nitrogen removal and the genetic potential for nitrification and denitrification, determined using quantitative polymerase chain reactions (qPCRs) of the nitrification gene amoA and the denitrification genes nirS/K, were evaluated in microcosms containing water from a eutrophic lake with or without E. crassipes. The results showed that total nitrogen (TN) losses on day 70 of the experiment were similar in all treatments but the uptake by E. crassipes resulted in the rapid (within 24 h) removal of TN and NH4+-N. In microcosms containing E. crassipes, the abundance of amoA increased whereas the abundances of nirS/K decreased. The T-RFLP (terminal restriction fragment length polymorphism) profiles showed that Nitrosomonas dominated the ammonia-oxidizing prokaryotes, based on the DNA and RNA levels of the targeted genes. The E. crassipes cultivation can be used to achieve fast and efficient reductions in NH4+-N concentrations in eutrophic water bodies. While this aquatic macrophyte may not be essential to N removal, considering the potential toxicity of NH4+-N, both aquaphytes and microbes should be fully exploited in the restoration of freshwater ecosystems.
Keywords: Eichhornia crassipes; T-RFLP; amoA; nirK/S; nitrogen.