Allelopathic Effect Of Solidago Canadensis On Performance Of Native And Invasive Triadica Sebifera Ecotypes

Novel Weapon Hypothesis suggests that invasive plants may release several special chemicals,which could inhibit the growth of its companion species,from their bodies into environment.This process is called allelopathy,an important mechanism of plant invasion,and the chemicals which are produced by invasive plants are called allelochemicals.Although the Chinese tallow tree(Triadica sebifera),a threatening invasive woody species throughout the southeast of the United States,has been proved that it has weak allelopathic effect on native species,there were few studies focused on the sensibilities of its different ecotypes towards allelopathy from other plants.Solidago canadensis,an exotic perennial forb which severely invades in China,has strong allelopathic effect which could well suppress its surrounding species.In this study,we used native and invasive ecotypes of Triadica sebifera as target species,and chose native and invasive ecotypes of Solidago canadensis as allelochemical sources.In order to better understand the variable sensibilities of these two Triadica sebifera ecotypes to allelopathy,we had conducted experiments which included allelochemicals identification,lab incubation experiments,pot experiments and soil nutrients analysis.Our study mainly included four aspects:(1)Allelochemical identifications of native and invasive Solidago canadensis;(2)allelopathic effects of Solidago canadensis on seeds germination and seedling growth of native and invasive Triadica sebifera ecotypes;(3)the interactive effect of rhizosphere microbes and allelochemicals on seeds germination and seedling growth of native and invasive Triadica sebifera ecotypes;(4)variability of soil nutrient contents under the mixed effects of allelopathy and Triadica sebifera seedling growth.The results and conclusions are listed as below:1.Relative contents of allelochemicals are different between native and invasive Solidago canadensis.Comparing the relative contents of six identified substances which were existed in both ecotypes,four allelochemicals(Methyl stearate;13-Octadecenoic acid,methyl ester;Hexadecanoic acid,methyl ester;cubedol)were higher in invasive Solidago canadensis than native ones.Combined with previous research results,we concluded that the difference of allelochemical contents,not their categories,might be the reason why the allelopathic effect of invasive Solidago canadensis was stronger than native ones.2.Invasive Triadica sebifera ecotype is more sentitive to allelopathy from invasive Solidago canadensis.Under the allelopathic effect,invasive Triadica sebifera seeds has higher germination rate.After we used the charcoal to exclude the allelopathic effect,the changes of seeds germination rate and time,seedling growth rate for invasive ecotype were larger than native ones,which indicated that invasive Triadica sebifera were more sensitive to allelochemicals,and had an ability to increase nutrients utilization.3.The interaction between soil microbes and allelochemicals has positive effect on Triadica sebifera initial colonization.When the microbial effect existed,allelopathy increased Triadica sebifera seeds germination rates and decreased seeds germination time.Allelochemicals might have the ability to inhibit some soil pathogen activities,which helped initial estabilishment of Triadica sebifera.4.The increase of soil nutrient availability is a contributing factor which will help the successful establishment of Triadica sebifera under allelopathy.Under the allelopathy,Triadica sebifera seedling growth had increased soil organic matter contents.However,different ecotypes of Triadica sebifera had different effects on soil inorganic nitrogen content.Native Triadica sebifera ecotype could help add soil inorganic nitrogen content,while invasive Triadica sebifera ecotype had negative effect.This difference might due to the enhanced nutrients use capacity and increased seedling growth rate of the invasive Triadica sebifera ecotype.