The Effect Of Local Biotic Resistance On Aquatic Plants Invasion

Freshwater ecosystems are frequently threatened by the invasion of aquatic plants.The biotic resistance provided by local plant communities can effectively resist the invasion of exotic species.However,there are limited researches on the interaction between disturbance and biotic resistance of local plant communities currently;and there is still a gap in the study of the interaction between local periphyton communities and invasive submerged plants.Three common invasive aquatic species in middle and lower Yangtze River: Alternanthera philoxeroides(Mart.)Griseb.,Cabomba caroliniana Gray and Hydrilla verticillata(L.f.)Royle native to China are chosen in this study.We explored that the different living types of invasive aquatic species in various freshwater ecosystems respond to the biotic resistance provided by local plant communities and periphyton community from the perspective of biological invasion,and the influence of disturbance for biotic resistance,The findings are as follows:1.The high diversity and total coverage of local plant communities significantly inhibited the growth and invasion of A.philoxeroides,and reduced the length,biomass and coverage of A.philoxeroides.Moreover,the interaction between human activities and local biodiversity has significant effect on the coverage of A.philoxeroides.The branch length,dry weight and coverage of A.philoxeroides have a negative response to different gradients of local plant diversity and total coverage.The biotic resistance provided by the local plant community can inhibit the growth and invasion of A.philoxeroides.And the disturbance of human activities can weaken the biotic resistance of local plant communities and provide an opportunity for the spread and reproduction of A.philoxeroides.2.C.caroliniana treated with different periphyton communities showed significant differences in the density and composition of periphyton.C.caroliniana responded differently to diverse periphyton communities and responded negatively to periphyton communities attached to native aquatic species.The growth rate,regeneration and colonization abilities of C.caroliniana in the invasive periphyton community treatment were higher than those of the native and mixed periphyton community.Comparing with invasive periphyton community treatment,the native periphyton community decrease the number and length of adventitious root and the branch number of C.caroliniana by about 53%,62% and 44%,respectively.The periphyton community from native submerged macrophytes performed biotic resistance against C.caroliniana in short time period.However,with the native submerged macrophytes gradually dying in winter Taihu Lake,their periphyton community could perish and lose the resistance ability against the invasion of C.caroliniana.Such results partly explain the invasiveness of the C.caroliniana in the Taihu Lake in winter season.3.In the lotic freshwater river ecosystem,the treatments of different periphyton communities significantly effected the relative growth rate and regeneration capacity of H.verticillata.The native periphyton community had no biotic resistance to H.verticillata.Instead,during the short experiment period,the growth and regeneration capacities of the H.verticillata were increased,and higher proportion of resources were allocated to the branch regeneration.The native periphyton community had significant effect on the growth of H.verticillata,but the periphyton community attached to the H.verticillata had no significant effect on the growth of the native species E.najas.The periphyton community of native submerged plants can increase the propagule pressure of H.verticillata by increasing the potential asexual propagules to promote the invasion.The results showed that the biotic resistance provided by local plant community to invasive aquatic plants was positively correlated with the diversity and total coverage of local plant communities,which could be weakened by human activities.However,the biotic resistance from native periphyton community was not correlated with the diversity,and only works on invasive aquatic plants in lentic freshwater ecosystem.