Coexistence Mechanisms Of Invasive Plant Species And Native Plant Species As Well As The Effects And The Mechanisms Of Invasive Plant Species On Plant Community Under Co-invasion Condition

Invasive plant species have exerted a severe effect on the invaded ecosystems.However,multiple invasive plant species can co-invade in the same habitat as the number of invasive plant species increases.Further,the relevant researches present that the successful invasion caused by one invasive plant species can directly or indirectly create an environmental condition in the occupied habitat that beneficial to the successful invasion of the subsequent invasive plant species.Thus,the co-invasion of two invasive plant species is a common form of invasion in the occupied habitats that may pose multiple effects on the ecosystems.Nevertheless,the advanced variations in the species number of invasive plant species have the potential to alter the functional similarity and dissimilarity between invasive plant species and native plant species,plant taxonomic diversity,plant functional diversity,community stability,and community invasibility.However,the current related researches mainly focus on the ecological effects of a single invasive plant species and therefore ignoring the interactions between different invasive plant species.This study aimed to assess the functional similarity and dissimilarity between invasive plant species and native plant species under the co-invasion of two invasive plant species(i.e.,Erigeron annuus(L.)Pers.and Solidago canadensis L.).Further,the effects and the mechanisms of the co-invasion of the two invasive plant species E.annuus and S.canadensis on plant taxonomic diversity,plant functional diversity,community stability,and community invasibility were also examined by using the cross-site comparisons.The results of this study can further elucidate the driving mechanism of the co-invasion of the two invasive plant species E.annuus and S.canadensis.The results of this study can also lay a solid theoretical platform to construct the early warning,and prevention and control management of biological safety problems represented by biological invasion caused by invasive plant species under the background of socialism with Chinese characteristics in the new era.The main results of this study are as follows:1.The functional similarity and dissimilarity between invasive plant species and native plant species and the coexistence mechanisms under the co-invasion of the two invasive plant species E.annuus and S.canadensis(1)Invasive plant species and co-existing native plant species tend to converge functionally under E.annuus invasion.Hence,the functional similarity between invasive plant species and co-existing native plant species under E.annuus invasion supports the habitat filtering hypothesis.(2)Invasive plant species and coexisting native plant species tend to diverge functionally under S.canadensis invasion and the co-invasion of the two invasive plant species E.annuus and S.canadensis.Thus,the functional dissimilarity between invasive plant species and coexisting native plant species under S.canadensis invasion and the co-invasion of the two invasive plant species E.annuus and S.canadensis supports the niche differentiation hypothesis.2.The effects of the co-invasion of the two invasive plant species E.annuus and S.canadensis on plant taxonomic diversity,plant functional diversity,community stability,and community invasibility:(1)The invasion of the two invasive plant species E.annuus and/or S.canadensis,especially S.canadensis invasion,significantly decreases plant taxonomic diversity.(2)S.canadensis invasion and the co-invasion of the two invasive plant species E.annuus and S.canadensis significantly increases Mason's ? functional diversity.(3)E.annuus invasion significantly increases community stability.However,S.canadensis invasion significantly decreases community stability.Community stability under the co-invasion of the two invasive plant species E.annuus and S.canadensis is significantly higher than that under S.canadensis invasion.Thus,the co-invasion of the two invasive plant species E.annuus and S.canadensis antagonistically affect the community stability compared with their independent invasion.(4)Community invasibility under the co-invasion of the two invasive plant species E.annuus and S.canadensis is significantly lower than that under S.canadensis invasion but significantly higher than that under E.annuus invasion.Accordingly,the co-invasion of the two invasive plant species E.annuus and S.canadensis also antagonistically affect the community invasibility compared with their independent invasion.(5)Community stability is negatively correlated with community invasibility,and the invasion intensity and the relative invasiveness of invasive plant species.Further,community stability is positively correlated with Shannon's diversity,Simpson's dominance,and Pielou's evenness.(6)Community invasibility and the invasion intensity of invasive plant species are negatively correlated with the number of plant species,Shannon's diversity,Simpson's dominance,Pielou's evenness,and Margalef's richness.In addition,Community invasibility and the invasion intensity of invasive plant species are positively correlated with the relative abundance of invasive plant species.(7)The number of plant species,Simpson's dominance,and Pielou's evenness may be the main factors affecting the community invasibility.