Effects Of Enemy Suppression On The Growth Of Alien Invasive Plants And Its Establishment Of Invasive Plants In A Native

Biological invasion has become a global problem,which caused serious damage to ecosystem structures and functions such as the reduction of biodiversity,species extinction and habitat degradation.At present,global environment changes intensely,which resulting in the severe fluctuation of resoures(Soil nutrient,light,water,etc.)and Environmental conditions(temperature,humidity,etc.),then may change the original habitat characteristics of plant communities and affect the biological invasion pattern.There is a great argument about the invasion of alien plants against native plants with enemy suppression,some insist that enemy suppression is benifical to invasion of alien plants.However,more and more studies have shown that exotic plants are more susceptible than native plants with enemy suppression.In addition,not only the effects of insect pests and fungi on enemy suppression,but also related to the alien invasive of the morphological characteristics and defense mechanisms,these are worth exploring.We did two experiments.Experiment 1: in the individual level,ten pairs alien invasion plants and native plants were selected.Two competitive treatments : intraspecific competition(native + native、alien + alien)and interspecific competition(native + alien).The one enemy suppression treatment is blank control,another one of a broad-spectrum insecticide and a broad-spectrum sterilant mixture(a aboveground broad-spectrum insecticide,a underground broad-spectrum insecticide and a broad-spectrum sterilants mixed solution).Experiment 2: in the level of the community,a single alien invasive plant of nine alien species was planted in the center of the plastic flower pot,and six native species were planted around the target species.Nutrient treatments for a group of without nutrient,the other group of multipulse nutrient;enemy suppression treatments for one of the blank control group,another group of a aboveground broad-spectrum insecticide.The effects of nutrient heterogeneity and enemy suppression were investigated by measuring the number of ramets,biomass,root / shoot ratio,species richness and leaf C: N ratio.The effects of nutrient variability and enemy suppression on the effects of alien invasion plants on the individual and community.The results showed:1.At the individual level,the total biomass,stem biomass,root biomass and leaf biomass of alien invasive plants were significantly higher than those of native plants.The biomass,number of ramets,stem biomass and leaf biomass were significantly higher with enemy suppression than without natural enemies.The positive effect of enemy suppression on native plants of stem biomass was greater than alien invasion plants,significantly increased the root biomass of native plants with enemy suppression,but had no significant effect on the root biomass of alien invasion plants.The total biomass,number of ramets,stem biomass and leaf biomass of alien invasion plants in interspecific competition were higher than those of intraspecific competition,but opposite to native plants.Without enemy suppression,the interspecific competition of the native plants was significantly lower than that of the intraspecific ones,but opposite to the alien invasion plants;with enemy suppression,There was no significant difference between native and alien invasion plants in competitive treatments.It shows that without enemy suppression,alien invasion plants are more advantageous than native plants,and interspecific competition will enhance the competitiveness of alien species,but weaken the native plants.2.At the community level,the total biomass,root biomass,stem biomass and leaf biomass of alien invasion plants in nutrient variability were significantly higher than those of without nutrient,and the same trend as native plants.Nutrient variability reduces the evenness of biomass in the native community,meanwhile,the nutrient variability will increase the biomass ratio of the native community with enemy suppression.It suggests that nutrient variability increases the growth of invasive species and reduces the evenness of the native community,but is detrimental to the invasion of the native community with enemy suppression.