ORIGINAL ABSTRACT

The impacts of herbicide glyphosate (GLY) on submerged macrophytes remain unclear in small water bodies, which receive pollutants from rainfall runoff and return water from farmland irrigation. In this study, an experiment was conducted to investigate the changes in water quality, plant physiological parameters and epiphytic microbial community in wetlands with Myriophyllum spicatum exposed to GLY for 24 days. Compared to wetlands without plants, M. spicatum enhanced GLY, total phosphorus, total nitrogen and ammonium nitrogen removal in overlying water at 10 mg/L GLY, but 20 and 40 mg/L GLY impaired nutrients removal with prolonged exposure time. These results demonstrate that M. spicatum contributed to the GLY and nutrients removal. High GLY concentration increased the malondialdehyde content and relative electrical conductivity and decreased chlorophyll-a content in plant leaves. Shannon values did not change in prokaryotic community but decreased in eukaryotic community in epiphytic biofilm. The decreased niche breadths and numbers of disadvantaged taxa were observed compared to advantaged taxa in both prokaryotic and eukaryotic communities under GLY stress. Structural equation model reveals that GLY was negatively related to environmental parameters but positively related to nutrients and plant physiological parameters, while aquatic nutrients were related to eukaryotic community in epiphytic biofilm. GLY stimulated the glucose metabolism and glyphosate oxidase pathway in prokaryotic community but inhibited NAD/NADP-NADH/NADPH interconversion in eukaryotic community. These data highlight that restoration of M. spicatum in small water bodies can improve water quality in agricultural areas, given that GLY concentrations are always below 10 mg/L.