Allelopathy Effects And Autotoxicity Of The Soil Invaded By Ageratina Adenophora Sprengel (Compositae)

Ageratina adenophora Sprengel(Synonym:Eupatoriurn adenophora Sprengel)(Asteraceae), originally found in Mexico and Costarica,is a noxious invasive alien weed,and it has become widespread in many countries and regions.In these invaded countries and regions,this weed has caused serious economic loss and threatened native biodiversity,ecosystem integrity and even the health of human and livestock.Therefore,understanding the invasive mechanisms is essential to carry out the sustainable control of this weed.Guided with the review of the invasive mechanisms of alien plants and the spread characters of A.adenophora,effects of A.adenophora invasion on soil and effects of the soil invaded by A.adenophora on seed germination and seedling growth of native plants were analyzed,and the experiments of effects of soil with active carbon were designed to measure the effects of invasion-induced changes of soil on A.adenophora.The main results were showed as follows:1.Effects of A.adenophora invasion on native soil nutrition and soil componentsSoil nutrition and soil components were analyzed and compared in the five sites(Heavily invaded, Medium invaded,Newly invaded,Native plant and Non-invaded),and the results showed that soil NO₃^-N,NH₄⁺-N,available P and K content were significantly higher in heavily invaded site as compared to the newly invaded site.The amounts of several components in soil were changed.It indicated that A.adenophora changed soil communities,especially the soil nutrition;some matters were probably released by A.adenophora,creating inhibition to native plants.2.Effects of A.adenophora soil on seed germination and seedling growth of upland riceEffects of the soil invaded by A.adenophora,in different years and the soil extracts on seed germination and seedling growth of upland rice were tested in laboratory.The results indicated that the soils and methanol extracts in the five sites had inhibition on seed germination and seedling growth.The longer Crofton weed invaded,the stronger inhibiting effects were.The inhibition to upland rice followed the order:Heavily invaded＞Medium invaded＞Newly invaded＞Native plant soil,as compared to the Non-invaded soil.The inhibition of the soil extracts showed similar resulets.3.Effects of A.adenophora soil within active carbon on upland riceThe components of extracts of active carbon from A.adenophora soil were analyzed,and effects of A.adenophora soil extracts within active carbon on seed germination and seedling growth of upland rice were tested in laboratory,the results showed that extracts of active carbon from A.adenophora soil had inhibition on seed germination and seedling growth,and soil extracts within active carbon had little inhibition.It indicated that some components that were released by A.adenophora had inhibiting effects on seed germination and seedling growth of upland rice,which could be adsorbed by active carbon.4.Autotoxicity of A.adenophora soil on seed germination and seedling growthThe study about effects of the soil invaded by A.adenophora,in different years on its seed germination and seedling growth was experimented in the green house,and the results showed that the soil had autotoxicity on its seed germination and seedling growth.The soil biota and soil within active carbon could weaken the inhibiting effects.It indicated that autotoxicity of soil invaded by A. adenophora was related to some components in soil that had allelopathy effects.