| With the acceleration of globalization,numerous alien species have been introduced into new environments.Biological invasions become more frequent,which harm global biodiversity,affect native ecosystem function,rise economic costs,and even threaten human health.Exploring how exotic species become strong invasive species in the introduced habitats and the impacts of biological invasions especially on ecosystem function have been key research topics in the ecology of biological invasions.Interactions between invasive plants and propagule pressure are important factors affecting the success of biological invasion,and may play roles together during the invasion process.Previous studies often focused on the impacts of biological invasion on certain ecosystem functions,such as primary productivity,nitrogen cycle,carbon cycle,litter decomposition and so on.However,the ecosystem can provide multiple functions at the same time,that is,ecosystem multifunctionality.The impact of biological invasions on ecosystem multifunctionality is less well studied.A mesocosm experiment was conducted to simulate the invasion process by planting invasive plants into native biota.Three Asteraceae invasive species containing Erigeron canadensis,Erigeron annuus and Bidens pilosa were selected.Different richness(1,2,3 invasive species)and abundance(i.e.,propagule pressure,12,24,48 invasive seedlings)of invasive plants were set.Ecosystem function parameters were measured and different approaches(averaging approach and threshold approach)were used to characterize multifunctionality.Therefore,we conducted this experiment to explore the influence mechanism of different invasive plant richness and abundance on invasion outcome,ecosystem function and ecosystem multifunctionality.The main results and conclusions are as follows:(1)The increasing richness and abundance of invasive plants inhibited native biomass and increased the proportion of invasive biomass to total community biomass,indicating facilitating invasion success.The proportion of invasive biomass to total community biomass increased by 27.8%and 72.8%with the richness of invasive plants,and increased by 63.5%and 157.7%with the abundance of invasive plants,which supported the invasional meltdown hypothesis and propagule pressure hypothesis.However,there was not a synergistic effect between the invasive interactions and propagule pressure during the invasion process.(2)Different ecosystem functions have different response trends to invasive plant richness and abundance.The richness of invasive plants could affect above-ground productivity,soil carbon content,soil phosphorus content and litter decomposition,while the abundance of invasive plants had no effect on ecosystem function.Therefore,the richness of invasive plants is a more important factor than the abundance of invasive plants.(3)With the increase of invasive plant richness,ecosystem multifunctionality increased first and then decreased,but invasive plant abundance had no effects on ecosystem multifunctionality.In addition to direct effects,invasive plant richness also have indirect effects on ecosystem multifunctionality mediating Shannon-Wiener index,Simpson index and community weighted mean height.Our study verified the invasional meltdown hypothesis and propagule pressure hypothesis,explored the synergistic effect of the interaction between invasive plants and propagule pressure on invasion process,and revealed the covariation relationship among functions by analyzing the effects of different invasive plant richness and abundance on invasion outcome,ecosystem function and ecosystem multifunctionality.These results could provide theoretical basis and scientific guidance for the control and management of invasive plants. |
