Plant species diversity affects plant nutrient pools by affecting plant biomass and nutrient concentrations in high-nitrogen ecosystems

Plant species diversity affects plant nutrient pools, however, previous studies have not considered plant nutrient concentrations and biomass simultaneously. In this study, we conducted an experimental system with 90 microcosms simulating constructed wetlands (CWs). Four species were selected to set up a plant species richness gradient (1, 2, 3, 4 species) and fifteen species compositions. The plant biomass, plant N, phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) concentrations and pools were analyzed. Results showed that, (1) plant species richness increased plant biomass, and the presence of Oenanthe javanicae increased while the presence of Reineckia carnea decreased plant biomass; (2) plant species richness only increased plant K and Mg concentrations of the communities and plant Mg concentration of the species, and the presence of O. Javanica increased while the presence of R. Japonicus decreased plant N and P concentrations of the communities; (3) plant species richness increased plant N, P, K, Ca, and Mg pools, and the presence of O. Javanica increased while the presence of R. Carnea decreased plant N, P, K, Ca and Mg pools; (4) the four-species mixture produced more biomass and nutrient pools than the corresponding highest specific species monocultures. In case the plant uptake can remove nutrients from CWs through harvesting, the results suggest that both nutrient concentrations and biomass must be considered when evaluating the accumulation of nutrients. Assembling plant communities with high species richness (four species) or certain species (such as O. Javanica) is recommended to remove more nutrients from CWs through harvesting.