Effects Of Allelopathy Of Invasive Species On Germination And Seedling Growth Of Submerged Plants Under Different Global Warming Scenarios

Biological invasion and global warming are two major environmental problems facing the world today.Allelopathy is considered to be one of the main means of invasion of invasive alien species.Invasive alien species affect the reproduction and growth of native species through allelopathy to promote their successful invasion.At the same time,human activities lead to the aggravation of global warming.According to the prediction of IPCC(2021),the average global surface temperature will increase by about 1.5 ℃ to 4 ℃ in the future.Global warming will change the phenology of plants and affect their reproduction and development.As the producer and the pioneer of aquatic ecosystem restoration,the germination and the seedling growth are two key periods in their life-history,and the research on them has important guiding significance for the restoration of aquatic ecosystem.Studies on the effects of allelopathy of invasive alien species on plants have been widely carried out,but the effects of allelopathy of invasive alien species on the germination and seedling growth of submerged plants under different global warming scenarios has not been reported yet.In this paper,two common submerged plants,Hydrilla verticillata and Vallisneria natans,were selected to study the allelopathic substances in the aqueous extracts of Eichhornia crassipes of 1 g/L,5g/L,25 g/L and the effects of three global warming scenarios of +1.5 ℃,+2.5 ℃ and +4 ℃,as well as their combined effects on the total germination rate,germination potential,germination index,vigor index,seedling height,root length,biomass and chlorophyll content of H.verticillata turions and V.natans seeds.The Williamson allelopathic effect index calculation method was used to evaluate the effects of different warming models on the allelopathic intensity of germination and seedling growth of two common submerged macrophytes.The main results are as follows:(1)The allelopathy of high concentration of E.crassipes aqueous extract significantly promoted the germination index,vigor index and plant height of H.verticillata turions and their seedlings.Allelopathy had no significant effect on the total germination rate,germination potential,vigor index,root length,biomass and chlorophyll content of V.natans,but the allelopathy of high concentration of aqueous extract of E.crassipes significantly inhibited the early cumulative germination rate of V.natans seeds.Medium and high concentration of extract had significant allelopathic inhibition on the germination index of V.natans.The extract of three concentrations all significantly inhibited the plant height of V.natans seedlings.The allelopathic effect of invasive alien species E.crassipes on the germination of the submerged plant propagules was species-specific,total germination rate,germination potential,germination index,vigor index,plant height,root length and biomass of H.verticillata turions and seedlings were significantly higher than that of V.natans seeds and seedlings,but the chlorophyll content of V.natans seedlings was significantly higher than that of H.verticillata seedlings.The analysis shows that when there is allelopathy of E.crassipes in the aquatic environment,H.verticillata turions show strong adaptability,and its germination and seedling growth will be significantly promoted,while the seed adaptability of V.natans is weak,and its seed germination will be significantly weakened in the early stage and the seedling growth will be significantly inhibited.(2)Different global warming scenarios had no significant effect on the germination of H.verticillata turions and V.natans seeds,but significantly affected the seedling growth of the two species.Under different scenarios,H.verticillata turions showed stronger adaptability than that of V.natans seeds,and the seedling growth of V.natans was more sensitive to temperature.(3)Under different concentrations of Water hyacinth extracts,global warming significantly promoted germination and seedling growth of H.verticillata and weaken the allelopathic inhibition of H.verticillata seedlings and turn into allelopathic promotion under the high global warming scenario.Global warming promoted the germination of V.natans,but weakened the allelopathic promotion of V.natans seedling growth and turn into allelopathic inhibition in all global warming scenarios.This study showed that compared with the sexual progagules of V.natans,the vegetative propagules of H.verticillata were more adaptive to the allelopathy of invasive species and global warming,and had better reproductive and seedling growth conditions.In addition,allelopathy promoted turion germination and seedling growth of H.verticillata,while inhibited seed germination and seedling growth of V.natans,and different global warming scenarios had different effects on the intensity of allelopathy between the two submerged plants.