Epiphytic algae mitigate the inhibitory effects of two aquatic invasive plants, Pontederia crassipes and Pistia stratiotes, on a submerged plant community
Exotic plant invasions and epiphytic algae potentially influence the growth of submerged plants. However, the effect of epiphytic algae on the resistance of submerged native plants to plant invasion is elusive. Therefore, we conducted this study to explore the effects of invasion scenarios and epiphytic algae on a submerged plant community (Hydrilla verticillata, Potamogeton wrightii, and Vallisneria natans) and water quality. We set up a control experiment with four invasion scenarios (no invasion, Pontederia crassipes invasion, Pistia stratiotes invasion, and co-invasion of P. crassipes and P. stratiotes) and two epiphytic algal states (with and without epiphytic algae). The presence of invasive plants resulted in significantly lower biomass (P < 0.01) of the submerged plant community without epiphytic algae than that with epiphytic algae, and the community biomass was lowest in the case of co-invasion. The presence of epiphytic algae resulted in native plants exhibiting competitive interactions only during co-invasion, whereas native plants exhibited competitive interactions at all times in the absence of epiphytic algae. Total nitrogen and phosphorus contents in water were lowest in the absence of invasion. Additionally, total phosphorus contents was highest in the presence of epiphytic algae and co-invasion. These results demonstrate that co-invasion strongly inhibits the growth of submerged plant communities more than single invasions, and epiphytic algae potentially offset this suppression. These findings will provide a scientific basis for submerged native plant restoration in wetland ecosystem.
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