Study On Invasion Mechanism Of Xanthium Italicum Based On Arbuscular Mycorrhizal Fungus And Population Genetic Diversity

Xanthium italicum is a widespread invasive weed in the world,and its invasion has a serious negative impact on the local ecosystem and economic development.Although some morphological and physiological studies have been carried out on its invasion mechanism,it has not been reported to reveal its invasion mechanism from the pointview of mycorrhizal fungal symbiosis and population genetics.Therefore,this paper studied the effect of arbuscular mycorrhizal fungus on the growth and development of X.italicum,and analyzed the genetic diversity and genetic structure of X.italicum population in China,in order to provide a theoretical basis for the study of the invasion mechanism of this invasive plant.The main results are as follows:1.Effects of an arbuscular mycorrhizal fungus Glomus mosseae on the growth of Xanthium italicum In this study,we investigated the influence of the mycorrhizal fungus Glomus mosseae on the physiological ecology,growth,and reproductive capacity of Xanthium italicum Moretti.We found that the chlorophyll content and net photosynthetic rate of the leaves of potted X.italicum whose rhizosphere soil was supplemented with G.mosseae was higher than those of the control group.Plants in the treatment groups had longer roots,shoots;more root biomass,stem biomass,fruit biomass;and more male and female inflorescences and fruits numbers relative to control plants.Additionally,the ratio of female to male inflorescence number was close to 2:1 in the treatment group as compared to 1:1 in the control group,suggesting an enhanced reproductive capacity in the former.G.mosseae applied to the soil also increased phosphorus absorption and accumulation in the roots,stems,and leaves of X.italicum.Thus,G.mosseae promotes the growth and reproduction of X.italicum and thereby enhances its competitiveness and capacity for colonizing a new habitat.2.Study on genetic diversity and genetic structure of Xanthium italicum populations in ChinaTo evaluate the genetic variation within and among populations of the alien invasive weed X.italicum in China,and to provide a theoretical basis for its invasion mechanism.For that,we employed inter-simple sequence repeat?ISSR?markers to explore the genetic diversity and genetic differentiation of 185individuals sampled from 10 populations.Eight selected primers yielded a total of 76 bright and discernible bands.X.italicum showed an intermediate genetic diversity at the population level?percentage of polymorphic loci?PPL?=60.26%,Nei's genetic diversity?H?=0.2098,Shannon's information index?I?=0.3129?.However,the genetic diversity at the species level was significantly high?PPL=100%;H=0.3673;I=0.5425?.The coefficient of gene differentiation(G_ST,41.4%)and analysis of molecular variance showed that genetic differentiation mainly occurred within populations?77.28%?.The estimated gene flow?Nm,0.7085?and Mantel test indicated that genetic differentiation in the populations may primarily come from genetic drift and anthropogenic activities.Our results revealed the high genetic diversity of X.italicum,which may help explain its invasion success in China.