Effects of plant diversity and sand particle size on methane emission and nitrogen removal in microcosms of constructed wetlands

Abstract To find an effective approach that improves nitrogen removal while reducing methane (CH 4 ) emission during the process of wastewater treatment in constructed wetlands (CWs), we conducted a microcosm experiment simulating CWs with two treatments. The first treatment was plant diversity (species richness and identity), and the second treatment was substrate sand particle size (fine sand and coarse sand). Results showed that, (1) the range of CH 4 emission in fine sand microcosms (−8.46 to 21.03 mg CH 4 m −2  d −1 ) was much greater than that in coarse sand (5.06 to 6.85 mg CH 4 m −2  d −1 ); (2) in coarse sand microcosms, plant species richness increased nitrogen removal ( P 4 emission ( P  > 0.05); (3) in fine sand microcosms, species identity surpassed species richness as a key driver of CH 4 emission, and the presence of Oenanthe javanica significantly decreased CH 4 emission, whereas the presence of Rumex japonicus notably increased CH 4 emission ( P P Phalaris arundinacea monoculture in fine sand microcosms had a high N removal and low CH 4 emission. Overall, we conclude that the best combination of low CH 4 emission and high N removal rates could be achieved in fine sand microcosms with special plant species as P. arundinacea .