Abstract
Many ecosystems may suffer from both nutrient enrichment and exotic plant invasions simultaneously. Much has been known that nutrient inputs can promote growth and expansion of exotic invasive plants in wetlands, and that allelopathic effects of the exotic invasive plants can inhibit the growth of coexisting native plants, contributing to their invasion success. Thus, we hypothesized that allelopathic effects of exotics on natives in invaded ecosystems can be enhanced by nutrient enrichment. To test this hypothesis, we conducted two greenhouse hydroponic experiments. One is the monoculture experiment in which a widespread exotic invasive perennial Alternanthera philoxeroides and a native perennial Ludwigia peploides subsp. stipulacea in monoculture were subjected to five levels of nutrient supply. The other is the mixture experiment in which the two species in mixture were subjected to five levels of nutrient supply, each with and without activated carbon addition. Both A. philoxeroides and L. peploides grew better under higher level of nutrient availability in monoculture experiment. In the mixture experiment, A. philoxeroides formed less total and root biomass while L. peploides formed more in response to activated carbon addition and all of the responses had larger degree at higher level of nutrient availability, indicating A. philoxeroides had significant allelopathic effects on L. peploides and the effects was significantly enhanced by nutrient enrichment. Such results support our hypothesis and reveal a novel mechanism for exotic plant invasion in eutrophicated and invaded wetlands, i.e. nutrient enhancement of allelopathic effects of exotics on natives.
Highlights
Wetlands can or potentially offer many ecosystem services to human society [1, 2]
Nutrient enhancement of allelopathic effects around the world eutrophication has been leading to wetland ecosystem degradation [8,9,10,11], which is often characterized by biodiversity losing and productivity decreasing [12,13,14]
Under the same nutrient level, total biomass, root biomass, stolon biomass and leaf biomass of A. philoxeroides were significantly smaller than those of L. peploides (Fig 1; Table 2), and such interspecific differences in total biomass, root biomass, stolon biomass and leaf biomass significantly enlarged with the elevation of nutrient level (Fig 1; Table 2)
Summary
Wetlands can or potentially offer many ecosystem services to human society [1, 2]. Human-induced municipal sewage discharging, agricultural fertilization [3, 4], and/ or atmospheric nitrogen deposition [5] may increase nitrogen and/or phosphorous loading to wetlands, causing water eutrophication of the ecosystems. This is true in urban and suburban wetlands [6, 7]. Previous studies found wetlands become more susceptible to exotic plant invasions after suffering from human disturbances like eutrophication due to nutrient accumulation [12, 16, 17]. Understanding how wetland ecosystems respond to nutrient accumulation and plant invasion can greatly help ecosystem management and governance of wetlands [6, 24]
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
