Effects of plants and soil microorganisms on organic carbon and the relationship between carbon and nitrogen in constructed wetlands

Constructed wetland is an ideal place for studying the effects of plants and microorganisms on the nutrient cycling and carbon–nitrogen coupling in wetland for their clear background. This study examined both bare plots and others with plants (Phragmites australis or Typha angustifolia) in constructed wetlands and vegetation and soil samples were collected to investigate the effects of plants and soil microorganisms on carbon and nitrogen content. Results showed that the soil organic carbon content was high in plots with high plant biomass, and the increase of soil organic carbon driven by plant biomass was mainly from light fraction organic carbon (LFOC). Correlation analysis and redundancy analysis (RDA) suggested that plants play an important role in the cycle of carbon and nitrogen elements in constructed wetland soils, and that plant nitrogen components were key factors influencing wetland soil carbon and nitrogen. In addition, this study found that most of the main microbial taxa were significantly correlated with dissolved organic carbon (DOC), ammonium nitrogen (NH4+), and nitrate and nitrite nitrogen (NOx−) indicating that microorganisms might play an important role in regulating soil element cycles in constructed wetlands by affecting the metabolism of activated carbon and reactive nitrogen. This study has implications for increasing the carbon sink of constructed wetlands to mitigate the effects of global warming.