Study On Invasion Mechanism Of Two Typical Exotic Plants Based On Allelopathy And Stoichiometry

The invasion mechanism of alien plants is a hot issue in the global ecological environment research today.Bidens pilosa and Wedelia trilobata are two very typical vicious invasive weeds in the Subtropical South China,which have caused serious economic losses and ecological damage.This study took B.pilosa and W.trilobata as the main research objects to explore the growth competitiveness of invasive plants from the perspective of allelopathy;Exploring the energy distribution trends and nutritional strategies of invasive plants in the invasive ecological process from the perspective of plant organs(root,stem,leaf)and rhizosphere soil stoichiometry;From the perspective of soil physical and chemical properties,the study on the changes of the soil environment of the invaded area was expected to reveal the competitiveness and invasiveness of B.pilosa and W.trilobata,and provided a theoretical basis for effectively preventing and controlling the invasion of alien plants and maintaining the stability of the ecosystem.The petri dish method was used to study the effects of extracts from the roots,stems,leaves,and flowers of B.pilosa and W.trilobata on the seed germination and seedling growth of the recipient plants;Using potassium dichromate external heating method,kjeldahl method,molybdenum-antimony anti-colorimetric method,alkali-diffusion method for B.pilosa and its associated species Alternanthera philoxeroides and W.trilobata and its associated species Ageratum conyzoides of C,N,P in root,stem,leaf and rhizosphere soil;Indophenol blue colorimetric method,3,5-dinitrosalicylic acid colorimetric method,potassium permanganate method,etc.were used to determine rhizosphere soil urease,invertase,celluloseas,water content and PH were measured.The main results were as follows:1.The extracts of different organs of B.pilosa had an inhibitory effect on the seed germination and seedling growth of W.trilobata,thus improving its invasiveness and competitiveness;The flower extract from W.trilobata significantly inhibited the seed germination of B.pilosa,and the extracts from different organs can promote the growth of B.pilosa seedlings to a certain extent.;Both of them had allelopathic inhibitory effects on the seed germination and seedling growth of the weakly invasive plant Eclipta prostrata,which made it dominant in the community and then colonized and spreaded rapidly.2.B.pilosa and W.trilobata invaded areas were low-N and low-P habitats.The soil organic matter accumulates in this intrusion area,and the net mineralization rate of P element was relatively strong;The two plant distributed more N elements to the leaves during the growth process,B.pilosa dispersed more C elements to the stems and leaves,and more P elements to the roots and stems,and the various organs were coordinated and fully utilized nutrient resources and rapid growth;Compared with the associated species,the P content in the roots and stems of B.pilosa and the stems and leaves of W.trilobata were higher,and the C : P and N : P of the different organs of the two were lower.Among them,the C : P of B.pilosa leaf and the N : P of W.trilobata leaf was higher than they roots and stems,indicating that both had a higher growth rate.3.B.pilosa and W.trilobata root C and stem C,root C : N and C : P were positively correlated,while B.pilosa stem C : N and N : P were negatively correlated,W.trilobata stem C : N and C : P were positively correlated,the energy distribution of the two was conducive to the growth of roots and stems what in line with the appropriate trade-off strategy;The content of N and P in B.pilosa root was positively correlated with the content of P in soil.Its invasion enhances the absorption and utilization of P element in soil,and then growed and expanded rapidly;The content of C in the roots and stems of W.trilobata was negatively correlated with soil AP,the roots and stems had differences in soil nutrient requirements and acquisition strategies.4.The activities of urease,catalase and celluloseas in the rhizosphere soil of B.pilosa and the activities of urease,invertase and celluloseas in the rhizosphere soil of W.trilobata rose significantly with the increase of the degree of invasion;The soil water content of W.trilobata was height degree>light degree,and the soil PH of B.pilosa was light degree>height degree;The activities of catalase and celluloseas in rhizosphere soil of B.pilosa were negatively correlated with soil p H.The activities of celluloseas in rhizosphere soil of W.trilobata was positively correlated with soil P,AP content and water content.Both improved the activity of different enzymes in the soil,promoted the circulation of soil nutrients,changed the soil environment,and created favorable rhizosphere nutrient conditions for themselves.