Nitrogen removal and abundances of associated functional genes in rhizosphere and non-rhizosphere of a vertical flow constructed wetland in response to salinity

Abstract

It investigated the nitrogen removal performance and the abundances of nitrogen functional genes in the rhizosphere and non-rhizosphere when vertical flow constructed wetland (VFCW) was used to treat brackish eutrophic water. The results demonstrated that both total nitrogen (TN) and ammonia nitrogen (NH4-N) removal efficiencies decreased with the salinity increasing from 0.05% to 1.0%. However, the removal efficiency of nitrate nitrogen (NO3-N) remained more than 93%. It was found by quantitative real-time polymerase chain reaction (qPCR) that abundances of amoA, nosZ, napA, nirK and nirS were greater in the rhizosphere than in the non-rhizosphere at the salinities of 0.05%, 0.5% and 1.0%. As the salinity increased, the abundance of amoA reduced. It indicated that the salinity inhibited the growth of ammonia oxidizing bacteria (AOB) and further hindered the nitrification, which resulted in the deterioration of TN removal performance. The abundances of nosZ, napA, nirK and nirS in the rhizosphere and non-rhizosphere were the highest at 1.0% salinity. The denitrifying bacteria might adapt to the salinity stress, which guaranteed high NO3-N removal efficiency.