Relationship between nitrogen transformation and its related genes: comparison among riparian, marsh, and full-scale constructed wetlands

Abstract

Wetlands are known as effective ways for nitrogen pollutants removal. Three types of wetlands (riparian, marsh, and full-scale constructed wetlands (CWs)) were investigated in this study. Research endeavor was focused on: (1) the abundances and distribution of functional microbes in different kinds of wetlands, and (2) the relationship between nitrogen transformation and its related genes. Results from incubation experiments showed that the topsoil (0–20 cm) of riparian wetlands was more efficient for reducing ammonium, with a rate of 1.50 μg g−1 h−1, than the subsurface (20–40 cm). It was also found that full-scale CWs performed most effectively for the removal of nitrite (1.14/1.13 μg g−1 h−1) and nitrate (3.77/3.44 μg g−1 h−1). According to quantitative real-time PCR and principal component analysis, the highest NH4+-N transformation rate in the topsoil (0–20 cm) of riparian wetlands can be mainly attributed to the amoA and Nitrospira 16S rRNA genes. The similar transformation rates between two depths in CWs can be well explained by the similar abundances of all seven tested genes. The nitrogen transformation rates were similar between two depths of marsh wetlands, regarding the significant differences of tested genes. This is probably due to that the abundances of functional microbes in both depths were similar for the nutrient limits. Furthermore, the absolute abundances of the related genes were found to be influenced by the content of nitrogen and carbon in soil.