Response And Mechanism Of Alternanthera Philoxeroides On The Local Nature Enemy

To elucidate the invasion mechanism of invasive plantAlternanthera philoxeroides, explore how the aquatic plant rapidlyevolved to adapt the terrestrial and amphibious habitat, andinvestigate the response patterns of A. philoxeroides with differentecotypes to local natural enemy, the defoliation was used tosimulate the insect herbivory, photosynthetic capacity,morphological characteristics, stem structure, biomass andchemical defense substances of three A. philoxeroides ecotypeswere analyzed. The results were shown in the followings.(1) After defoliation, the photosynthetic rate of terrestrial A.philoxeroides decreased, while that of aquatic A. philoxeroidesincreased. The WUE, Ci, Trof three A. philoxeroides ecotypesshowed the same regular trend. Defoliation treatment couldsignificantly inhibit the growth of A. philoxeroides, reduced branchnumber, stem number, stem length and total leaf area, especiallyreduced the stem length of terrestrial A. philoxeroides.(2) After defoliation, terrestrial A. philoxeroides’s corticalthickness and cortical thickness ratio increased, while the corticalthickness and marrow cavity increased for the amphibious andaquatic. The other stem structure characteristics of three A.philoxeroides ecotypes decreased. (3) After defoliation, the biomass of three ecotypes A.philoxeroides significantly decreased and improved the root shootratio, indicating that A. philoxeroides would allocate resource tounderground part in order to support the above-ground growth.(4) After defoliation, the total sugar and the lignin contents ofthree A. philoxeroides ecotypes decreased, while he total phenolicand tannins contents increased. After defoliation, the terrestrial A.philoxeroides showed significant trade-off between resistance andtolerance, while no significant trade-off was found in theamphibious and aquatic A. philoxeroides.In conclusion, defoliation treatment could inhibit the growth ofA. philoxeroides to a certain extent, prevent the spread, especiallyhave significant effects on terrestrial A. philoxeroides, which canbe considered as a potential biological control. The results alsoshows that, when A. philoxeroides meet local herbivorous insectfeeding or potential threats to the leaf, two kinds of defense style(the resistance and tolerance) combined to resist the environmentpressure and the resistance and tolerance has relevance to acertain extent.In addition, in order to study the evolutionary changes of invasiveplant A. philoxeroides after many generations, discriminate thechanges were caused by rapid evolution, or just the phenotypicplasticity, a laboratory simulated evolutionary method was usedand the morphological structure, biomass and chemical defensesubstances were analyzed. The results were shown in thefollowings.(1) With the increasing of culture generations, the branch number of terrestrial A. philoxeroides increased, while the stemlength, stem number, leaf number, leaf area, root length and rootvolume decreased. With the increasing of culture generations, thebranch number, stem length, nodes number, leaf number and rootvolume of aquatic A. philoxeroides increased, while the leaf areaand root length decreased.(2) With the increasing of culture generations, the stemdiameter of A. philoxeroides decreased, while the corticalthickness, collenchymas tissue thickness, vascular diameter andmedullar cavity diameter decrease.(3) With the increasing of culture generations, the totalbiomass decreased, while the growth rate of leaves decreased by3.64%,2.85%,2.76%and1.21%, respectively.(4) With the increasing of culture generations, the total sugarcontent and lignin content of A. philoxeroides decreasedsignificantly, and tannin and total phenolic increased. The tannincontent in four habitats increased by0.09%,0.11%,0.05%and0.14%, respectively, while the total phenolic contents wereincreased by1.71%,1.19%,1.88%and1.8%, respectively.In conclusion, these results indicatedwe believe that afterinvasion into the new area, A. philoxeroides in differenthabitatsinvasion of China, would evolved would develope differentstrategies in response to under the pressure of new enemystressies in different habitats.: the Tterrestrial A. philoxeroideswouldgrowth grow slowly and increase resistance to response toenvironment;, While, the aquatic A. philoxeroides play a roleinwould increase both resistance and tolerance, together to response to environment. Our studies results also show indicatedthat to stable, may have rapid evolution would happen at fourthgenerations. But More evidences of rapid evolution are on coming.