Interactive effects of nutrient availability, fluctuating supply, and plant parasitism on the post-invasion success of Bidens pilosa.
The post-invasion success of alien plant species is determined by many biotic and abiotic factors, but no study has tested the interactive effect of nutrient availability, fluctuating nutrient supply and parasitic plants. Testing this effect is important because parasitic plants are proposed as a promising agent for biocontrol of alien plant invasions. We constructed an experimental native community under constant or fluctuating conditions as well as high or low nutrient availability and let them be invaded by an alien annual plant Bidens pilosa or not and parasitized by Cuscuta australis or not. High nutrient availability significantly increased the invasion success of B. pilosa (as indicated by its increased biomass fraction, i.e., invader biomass divided by total biomass of all plants) by benefiting the invader more than the native plant community. Fluctuating nutrient supply also significantly enhanced the invasion success of B. pilosa by suppressing the growth of the natives while improving that of the invader. Parasitism by C. australis decreased the growth of the invader and thus its invasion success in the native community when nutrient availability was low and fluctuating, but parasitism had little impact under other nutrient conditions. Our study offers further evidence that high and fluctuating nutrient availability can increase the invasion success of alien plant species in native plant communities, but also demonstrates that the impact of parasitic plants depends on environmental conditions. Thus, reducing nutrient loading and the extent of fluctuating nutrient supply can help native plant communities resist alien plant invasions, but introducing parasitic plants may only be successful if reduced loads are also fluctuating.