Does species richness affect the growth and water quality of submerged macrophyte assemblages?

Abstract

Biodiversity commonly plays important roles in ecosystem functioning. While many studies have tested effects of species diversity on productivity, carbon and nitrogen cycling and resistance to biological invasion, few have examined how diversity of submerged macrophytes affects the water quality of aquatic ecosystems. We assembled aquatic microcosms with 1, 2, 3 and 4 submerged macrophyte species (Hydrilla verticillata, Ceratophyllum demersum, Myriophyllum verticillatum and Elodea nuttallii), and measured growth of the macrophytes and physical and chemical properties of the water (total nitrogen and phosphorus, transparency, dissolved oxygen content, chemical and biochemical oxygen demand) in the microcosms after 36 days. Species diversity of submerged macrophytes did not significantly affect biomass and the vegetative reproduction of the macrophytes or the water factors such as total nitrogen and phosphorus, chlorophyll a content, chemical and biochemical oxygen demand of the aquatic ecosystems. Exceptionally, the 3-species treatment had higher light transmittance than the monoculture and the 2- and 3-species treatments also ended up with higher dissolved oxygen compared to the 1- or 4-species treatment. However, since only functionally similar submerged macrophyte species were involved in this study, it is still difficult to draw clear conclusions. Therefore, we suggest to include multiple types of submerged macrophytes to test the effect of species richness on vegetation growth and water quality in future studies.