Phenotypic Plasticity And Adaptability Of Alien Invasive Plant Xanthium Italicum Moretti

When exotic plants arrive at the invading area from their native place of origin,their adaptability to the local environment determines their ability to survive,multiply and expand.Phenotypic plasticity is one of the strategies for plants to adapt to heterogeneous habitats and plays an important role in the adaptation of invasive species to new environments.Xanthium italicum Moretti has spread rapidly since its discovery in China in 1991 and has been found in Beijing,Hebei,Liaoning,Jilin,Shandong,Shanxi and Xinjiang.The habitats of its invading areas are various,such as farmland,desert,riverside,undergrowth and wetland,and the phenotypic characteristics of different habitats are quite different.In order to explore the role of phenotypic plasticity in its adaptation to heterogeneous habitats,different levels of soil nitrogen,soil moisture and light intensity were set up.Plasticity response of morphological characteristics,leaf photosynthetic pigments content,biomass and biomass allocation were analyzed to different conditions.We hope that these results can provide scientific basis for revealing the causes of the successful invasion of X.italicum.The results show that:Soil nitrogen had significant effects on morphological traits(height,base diameter,crown width and branch number),photosynthetic pigments(chlorophyll a,chlorophyll b and carotenoids),biomass(root biomass,stem biomass,leaf biomass,fruits biomass and total biomass),root-shoot ratio(R/S),biomass allocation(except stem mass ratio,SMR)and fruits number of X.italicum.The R/S,root mass ratio(RMR),and leaf biomass ratio(LMR)decreased significantly with the increase of soil nitrogen,while other phenotypic traits increased significantly with the increase of soil nitrogen.X.italicum has strong phenotypic plasticity to soil nitrogen.Crown width,content of photosynthetic pigments,biomass and fruits number have stronger phenotypic plasticity to soil nitrogen than other phenotypic traits.Soil moisture had significant effects on crown width,branch number,content of photosynthetic pigments,R/S and biomass allocation of X.italicum,but had no significant effects on plant height,base diameter,biomass and fruits number.The crown width,branch number,SMR and LMR increased significantly with the increase of soil moisture,while the content of photosynthetic pigments,R/S,RMR and fruits mass ratio(FMR)decreased significantly with the increase of soil moisture.Crown width,branch number,content of photosynthetic pigments and biomass allocation(except FMR)of X.italicum had strong phenotypic plasticity to soil moisture,while plant height,base diameter and fruits number had weak phenotypic plasticity to soil moisture.The effects of soil nitrogen and soil moisture on the phenotypic traits of X.italicum were interactive,and the increase of soil moisture could significantly improve the absorption and utilization of soil nitrogen by X.italicum.The plant height,base diameter,crown width,branch number,biomass and fruits number of X.italicum under HWHN(high water with high nitrogen)were significantly higher than those under LWHN(low water with high nitrogen)and HWLN(high water with low nitrogen).Soil nitrogen and soil moisture promoted each other.RMR and LMR under HWHN were significantly lower than those under LWHN and HWLN.The phenotypic plasticity of X.italicum to low soil nitrogen(or low soil moisture)environment is weaker than that to high soil moisture(or high soil nitrogen).The decrease of light intensity could significantly increase the plant height,crown width,specific leaf area(SLA),total chlorophyll content,chlorophyll/carotenoid and LMR of X.italicum,and significantly reduce the base diameter,branch number,chlorophyll a/b,biomass,FMR and fruits number.The effects of soil nitrogen and light intensity on the phenotypic traits of X.italicum were interactive.Increasing soil nitrogen level under low light intensity could significantly increase plant height,base diameter,crown width,leaf biomass,LMR and fruits number of X.italicum,but significantly reduce SLA,RMR and FMR.Under low light intensity,the phenotypic plasticity of X.italicum to soil nitrogen was weaker than that under high light intensity.In summary,phenotypic plasticity is an important strategy for X.italicum to adapt to heterogeneous habitats.X.italicum adapts to different soil nitrogen,soil moisture and light intensity environments through changes of morphological traits,photosynthetic pigments,biomass and its allocation.It has strong phenotypic plasticity for different environmental factors,and the interaction among environmental factors had a significant effect on the phenotypic traits of X.italicum.