Study On The Formation Mechanism Of Community Invasibility Underlying Forest Soils In The Kunyu Mountain

As an important component of ongoing global change,exotic plant invasions have been doubtlessly shown to be one of the major causes of biodiversity loss.Elucidating mechanisms regulating community invasibility remains a central goal of invasion ecology.The Biotic Resistance Hypothesis predicts that species-rich communities are more successful at resisting invasion by exotic species than are species-poor communities.That is to say,biodiversity is negatively correlated with community invasibility.But the relationship is not always true,known as the invasion paradox.Furthermore,evidences show that invasions are context-dependent and the success associated with invader-community interactions.However,how different community types influence the invasion of exotic plants by shaping the soil environments remains to be further studied.In this study,the effects of different types of forest community soils on the growth of invasive plants P.americana,and the contributions of dominant species to the effect through plant-soil feedback and litter pathways were studied.Thus,we explored how the dominant species in different communities synergistically shape the soil environments through the above-ground and underground pathways to affect the resistance to invasion.The main conclusions of the study are:(1)We found that allelopathy of natural forest soils can effectively resist P.americana invasion,and that low level of nutrients,especially of phosphorus,in the soils might be potential limiting factors for the plant growth.The profound conditioning of soil resources by exotic R.pseudoacacia based on tree traits(including allelopathy)facilitated further P.americana invasion.Allelochemicals from forest litter inhibited the germination of P.americana seeds,but pH played a major role in P.americana growth when these substances entered the soil.However,we have no evidence that late-successional forest soils exhibit strong allelopathy toward P.americana.(2)Forest and open area soil contexts were different in terms of nutrient availability,phenolic compounds,and soil microbes.Native and exotic species produced entirely different soil feedbacks to the invader,which were highly context-dependent.More specifically,natives and exotics growths have differently negative effects on P.americana in forest soil,which were related to the effects of soil biota.While,the growths of natives and exotics respectively have positive and neutral effects on P.americana in open area soil,which were both related to nutrient availability and the effects of soil biota.Furthermore,litter-mediated allelopathic legacy,over that of root exudates,of dominant Q.acutissima.caused the strongest inhibition on P.americana than other species.Combining previous results,we concluded that the context-dependent PSFs generated by dominant species can resist plant invasions,but the occurrence of invasional meltdown should be viewed in long-term context.Soil biota is the primary mechanism for explaining PSF in this study,and the operational coupling mechanisms were still context-dependent.Modification of soil biota by dominant species litter-mediated allelopathic context should be taken seriously.(3)The allelopathy of native and exotic species significantly differed and exerted variable effects on the soil properties(soil pH,available nutrients,and nitrogen cycle)and had variable allelopathic effects on the growth of P.americana.The changes in soil properties due to allelopathy were more important,as they affected the aboveground and belowground biomass accumulation of recipient invasive species by change in the biomass allocation strategies.The results suggested that the influence of dominant plants on the soil environment via allelopathy partly determines the community invasibility.These results suggested that the effect of dominant species growth performance on the soil environment determines the invasibility of communities.Dominant species litters mediated allelopathy both directly and indirectly through long-term modification of soil microbes in the plant-soil feedback affect the growth of P.americana.The effects were different between native and exotic plants,which may contribute to the community's invasibility.This study highlights the importance of vegetation feature,especially dominant species identity,for community invasibility.