The Effect Of Nutrient On Responses Of Two Aquatic Invasion Plants To Water Level,Herbivory And Clonal Integration

Eichhornia crassipes and Alternanthera philoxeroides are two of the most serious aquatic invasive species,which had invaded many areas of the world and caused severe influence on ecology and economy.With the rapid development of economy in China,water eutrophication and soil nutrient loading are becoming more serious.High nutrition could promote the growth and production of most alien species and aid their invasion.However,there is a lack of study on the effects of high nutrition on the overwintering and clonal integration ability of alien aquatic species.Therefore,the effect of water breakdown in winter on overwintering of Eichhornia crassipes under eutrophication were studied.Furthermore,compared with Alternanthera sessilis,the effects of clonal integration and herbivory on Alternanthera philoxeroides under different nutrition were studied.The results are as follows:1.High nutrient level significantly increased the growth of E.crassipes.,which led more and bigger plants,larger stem base and more storage.Floating E.crassipes performed the highest survival rate at high nutrient level among all treatments.On the contrary,floating E.crassipes could not survival at low nutrient level.Water breakdown significantly decreased the survival rate of E.crassipes at high nutrient level,while it increased the survival rate at low nutrient level in winter.2.The morphological traits and biomass allocation pattern of A.philoxeroides were significantly different with that of A.sessilis.A.philoxeroides allocated more biomass to root,while A.sessilis allocated more biomass to stem.The branching number of A.sessilis significantly higher than that of A.philoxeroides.Nutrient had significant effects on compensatory growth of A.philoxeroides and A.sessilis.High nutrient level increased the new leaf number,new node number and biomass.High nutrient also increased the percentage of stem biomass and decreased the percentage of leaf biomass.This allocation pattern was more obvious under stolon severance treatment..Herbivory had significant negative influnce on the two species.Herbivory decreased Fv/Fm of the two species especially of A.philoxeroides.Herbivory also inhibited the compensatory growth significantly,which decreased the mean biomass,new leaf number and new node number of the two species.Stolon severance had less influence on the two species,and clonal integration showed no significant advantages.A.philoxeroides showed greater ability of compensatory growth.The mean biomass,total leaf number,new leaf number and new node number of A.philoxeroides were higher than those of A.sessilis.In conclusion,high nutrition significantly promoted the performance of growth and enhanced the overwinter ability of A.Philoxeroides and E.crassipes,thus increased the rapid spread of these two invasive speices.