Impact Of Cuscuta Australis On Different Invasive Plants

Biological invasions have serious impacts on the construcutres and thefunctions of the ecosystem. Cuscuta spp. species can inhibit the growth ofinvasive plants and promote the recovery of the native community and are takenas the potential biological control agents. In order to explore the impact andmechanisms of parasitic plants on the invasiveness of invasive plants, weanalyzed the responses of congeneric invasive and native species paires to theparasitism of Cuscuta australis at three different levels. We also analyze thedynamics of the community diversity and the productivity of the communitycomposed of different invasive species and native species in order to explorethe effect of parasitic plants on the invisibility of the community. The results areshown as the followings.1. In the pot experiment, when the invasive species are Chenopodiumambrosioi and Alternanthera philoxeroides, the winding number and the coverof the Cuscuta australis increase with the parasitic time, and grow faster thanthose parasitized on native hosts. When the invasive species is Wedeliatrilobata, the parasitic plants grow slower than those on native species. tWhenthe invasive species is Paspalum conjugatum, parasitic plants grow worser andworser after parasitization and begin to die on the fourth day and all die in twoweeks. This suggested that the pereference of parasitic plant Cuscuta australison plants were difference, which might depends on the growth traits of theplants and need further test.2. The invasiveness of invasive and native species was inhibited at differentlevel by the parasitism of C. australis. The total biomass of invasiveChenopodium ambrosioi, Alternanthera philoxeroides and Paspalum conjugatum and native C. serotinum and W. chinensis reduced significantlyafter the parasidizatoin of C. australis. But the total biomass of the otherinvasive and native species did not changed significantly. The biomass of thereproductive organs and the number of seed of C. ambrosioi were also inhibited.The biomass of the reproductive organs and the number of seed of C. ambrosioiand P. distichum were inhibited by the heavily parasitized C. australis. Theresults suggested that the impact of parasitic plants on the host plants isspecies-specific, which depend on the traits of plant species, such as growthtraits of host plants. With the increasing of the degree of parasitism, theinvasiveness of hosts was inhibited more seriously. This suggested that thereshould be a certain relationship between the invasiveness of invasive speciesand the parasitism level.3. Comparing the the growth of parasitic plants on the hosts with differentages, we found that the response value of the morphological index,photosynthetic capacity and the biomass of Bidens pilosa to parasitismgradually decreased with the increasing of the age, indicating the graduallydecreasing of the inhibitory effect of parasitic plants on hosts. The resultssuggested that in different growth stages of Bidens pilosa, the inhibit effect issignificant in the early stage.4. The effect of C. australis on the growth of B. pilosa with or withoutaddition of fertilization were compared and the results showed that fertilizationsignificantly increased the root biomass, stem biomass, leaf biomass and totalbiomass, leaf mass ratio, specific leaf area and the chlorophyll content of B.pilosa, but significantly reduced the root shoot ratio and root mass ratio. Therewere significant positive relationships between the biomass of C. australis andthe total biomass, leaf mass ratio, specific leaf area and the relative chlorophyllcontent of B. pilosa, while there were significantly negative relationshipsbetween the biomass of C. australis and the root mass ratio, the root shoot ratio.Fertilization can change the biomass allocation patterns of hosts as well aschange the light resources capture ability, which can change the tolerance ofhosts to the parasitism of C. australis. 5. The annual dynamics of the artificial communities with and withoutparasitic plants were compared and the results showed that parasitism of C.australis can reduce the important value of the invasive plant and increased thespecies diversity of the communities. Excpet Solidago Canadensis, theproductivity of the communities decreased after the parasitism. The speciestypes of the invasive and native plants in the communities can affect the effectof the parasitism on the invisibility of the communities. The results suggestedthat the invisibility of the community composed of native species belonging toAsteraceae or Leguminosae which are preferred by the parasitic plants.