A novel plant-girdling study in constructed wetland microcosms: Insight into the role of plants in oxygen and greenhouse gas transport

Constructed wetland (CW) wastewater treatments could be potential hotspots of greenhouse gas emissions to the atmosphere when removing pollutants, and the existence of wetland plants is an important factor in carbon and nitrogen cycling in CWs. In this study, the wetland mesocosms planted with Phragmites australis were conducted by using the novel plant-girdling method to assess the role of plants in potential O2, N2O, CO2 and CH4 production and transport in treating wastewaters with and without carbon sources. The system with girdling plant showed an obvious decrease of O2 release, but the higher O2 release rates of 157.78 mg O2 m−2 d-1 was obtained with an addition of carbon source. Average values of N2O, CO2 and CH4 fluxes in wetland mesocosms were 0.85 mg N2O m−2 d-1, −152.4 mg CO2 m−2 d-1 and 0.31 mg CH4 m−2 d-1, respectively when girdling and adding carbon source. Girdling plants and adding carbon source facilitated the removal of organics and nitrogen. Our study indicated that girdling wetland plants stimulated transformation of organics and nitrogen by net oxygen release from plants, but it could bring a raising greenhouse gas emission, which provided new slights into an improved understanding of wetland plants functioning in greenhouse gas transport and pollutant removal in CWs for wastewater treatment.