Plant species richness enhances nitrous oxide emissions in microcosms of constructed wetlands

The coexistence of multiple plant species is an important factor influencing nitrogen removal in constructed wetlands (CWs). However, the influence of plant diversity on nitrous oxide (N2O) emission from the CWs lacks research. In this paper, we examined N2O flux and related parameters in response of plant species richness in microcosms simulating CWs. Results showed that, N2O emissions increased with plant species richness (P < 0.05), ranged from 902 to 1848 μg N2O m−2 d−1; nitrogen removal, abundance of nitrite- and ammonia-oxidizing bacteria, nitrification rate, as well as nitrate reductase activities, also increased with species richness (P < 0.05); N2O emission increasing was more sensitive to plant species richness than nitrogen removal rate, however, there was no response in denitrification rates and denitrifier abundance to species richness (P > 0.05). Manipulation of plant species richness may provide an opportunity to increase the nitrogen removal efficiency in CWs, with an expense of simultaneously raising greenhouse gas emission.