Invasion Resistance Of Dominant Plants From Different Communities In Jiaodong Peninsula

Exotic plant invasion has threatened the ecological safety seriously in Jiaodong peninsula in the past few years.Scientists have made great efforts on the invasiveness of many exotic plants.While on the perspective of ecological control,more efforts should be made on the invasion resistance of native dominant speices.This will not only show the possibility of ecological control of a specific exotic species,but also provide theortical basis for how to construct high-resistance plant communities and therefore be benifitial to practical application in the field.In the present study,two invasive plants,Rhus typhina and Phytolacca Americana were chosen as target species.Six dominant tree species from different communities,namely Quercus acutissima,R.chinensis,Amorpha fruticosa,Robinia pseudoacacia,Pinus densiflora,and P.thunbergii were selected as test species.We evaluated the particular contributions of plant-soil feedback(PSF)generated by the different dominant species on community invasion resistance,explored the roles of plant allelopathy in the PSF processes.We aim to reveal the mechanisms underlying the effects of PSF on the invasion resistance of communitiets.The main results were showed as follows:(1)Laboratory bioassay and pot experiments were conducted to compare the allelopathic effects of 4 dominant plant species on different growth stages of invasive plant R.typhina.The results showed that the allelochemicals of the root leachates from native species Q.acutissima significantly reduced the germination speed of the seeds of R.typhina.Compared with A.fruticosa and R.pseudoacacia,which originated in the Americas,Asian species Q.acutissima and P.thunbergii inhibited the biomass accumulation of the R.typhina seedlings.(2)The PSF experiments were conducted in two stages.In the first stage,the invasive plants and the dominant plants from different forest types were planted in the common garden under the same soil conditions.The results showed that the soil physicochemical properties,enzyme activities,and microbial community structure under different planting groups showed significant differences after the 75-day planting period.The principal component-cluster analysis was used to analyze the data on soil properties.The soil fertility levels were higher when planted with native plant species(R.chinensis,Q.acutissima,P.densiflora)than when planted with the plant speices originated from the America(two naturalized plants,A.fruticosa,R.pseudoacacia,and two invasive plants R.typhina,P.americana).The soil planted with thefour species originated from America(A.fruticosa,R.pseudoacacia,R.typhina,and P.americana)were more similar in nutrient structures.The soil planted with the two broad-leaved plants originated from Asia(R.chinensis and Q.acutissima)were more similar in nutrient structures.The soil planted with the two needle-leaved plants originated from Asia(P.densiflora and P.thunbergii)and the blank control group were more similar in nutrient structure.Obviously,in our study,it seemed that plants from the same origin had more similar influence on the soil nutrient structures.Exotic plants used a larger amount of soil nutrients and used soil nutrients more efficiently to promote their own biomass accumulation,which may be one of the main reasons for their successful colonization or invasion.The effect of different plants on soil microbial community structure showed that after the 75-day period of growth,the abundance and diversity of soil microbial species in different treatments changed to varying degrees compared with those in the blank control group.The rhizosphere effects of various plants changed the composition of soil microbial communities to different degrees,which might increase the types and quantities of certain beneficial microorganisms that facilitated their subsequent growth.(3)In the second stage of the PSF experiments,each plant species was planted again in the various soils from the previous stage.Then,we compared the plant biomass when plants were grown under its own soil with that when plants were grown under other soils.Multiple regression analysis was used to analyze how plants affected the growth of their own and other plants by changing the soil microecological environments.The results showed that after the second stage of planting,different treatments had different effects on the plant biomass,which may be related to plant nutrient requirements,and the inconsistency with field observations might prove to some extent that the plant allelopathy played a role in the community resistance to invasion.Physical and chemical methods have obvious disadvantages in the prevention and control of exotic invasive plants.It's also very dangerous to introduce some new exotic species,such as insects,to control the invasive plants.Our results indicated that allelochemicals secreted by some native plants(such as Q.acutissima)could suppress the growth of invasive plants to a certain extent.It may be effective to use some native plant species,which has significant allelopathic inhibitory effects on invasive plants,to construct highly resistant plant communities in order to ecologically control exotic plant invasions.