The Main Physiological And Ecological Mechanism Of The Notorious Invasive Plant Wedelia Trilobata Choosing Asexual Reproduction

With the rapid development of human activities, a number of extotic species have been introduced from its native habitat and quickly established self-sustaining populations and become invasive species. Invasive species can significantly affect the structure and function of ecosystems, and shift the evolution of native species. In plant life history, the allocation of resources to maintain, growth and reproduction is very important. Because the strategy is various, the modes of reproduction affect every aspects of invasion of alien plants. The establishment and dispersal of alien plant are involved in reproduction. Therefore, the reproduction strategy is very important for plant invasion. There are various factors affecting plant reproduction, including internal and external factors.Wedelia trilobata, as an invasive species, spread its habitat in the south of China. This study focused on the main ecological mechanism of invasive species W. trilobata choosing clonal reproduction strategy, and discussed the reproduction strategy and effects of endogenous gibberellin and litter on the choosing of reproduction strategy, in order to explain the invasion mechanism of W. trilobata. The main results are as follows:1) In the field survey, we found W. trilobata flowers all year around, and it can product numerous fertilized seeds. However, there are few Stedlings under its dense population, and few seedlings were found in the bare ground near to populations. In laboratory experiments, low light significantly inhibited seed germination. Leaf extracts also decreased seed germination and inhibited seedling growth, and significant interactions were found between low light and leaf extracts on seed germination. However, seeds were found to germinate in an invaded field after removal of the W. trilobata plant canopy.2) Leaf extracts of W. trilobata inhibited seed germination of two subject Asteraceae species, Eupatorium catarium and Lactuca sativa. Cultured with W. trilobata, the growth of these two subject species was significantly inhibited. Leaf extracts of W. trilobata promoted its own adventitious root growth and did not suppress its own ramet growth. Leaf extracts of W. trilobata increased its own competitive ability. Moreover, leaf extracts also increased the competitive responses of W. trilobata to E. catarium. Moreover, the leaf extract of W. trilobata increased its own adventitious root growth, and did not significantly affect its shoot growth. We also found that leaf extracts of W. trilobata could significant inhibit the hyphal growth of F. oxysporum and Rhizoctonia solani. The component analysis of leaf extract showed that there were many chemicals were reported to be allelopathic chemicals.3) In the control experiment, we found the application of GA could increase the number of ramet of W. trilobata. Through clonal integration, the belowground of both basal and apical part of W. trilobata take nutrients from soil to the young apical part. The GA application in the basal part could promote the whole individual’s growth, the connected ramets grew significant larger than the severed ones. In the different light condition, clonal integration promote the ramet growth which under week light. The clonal integration could relieve the weed light stress on the ramets.4) We found endogenous GA in W. trilobata was higher than that in W. chinensis. The reduction of endogenous GA repressed the adventitious root emergence and growth in the initial stage of W. trilobata culture and inhibited its shoot elongation and biomass. Whereas, adventitious roots of W. trilobata treated with exogenous GA emerged earlier and grew faster, and the endogenous GA level was positively correlated with the shoot length and adventitious root length of W. trilobata. In addition, treated with GA, the root activities of W. trilobata were increased. However, different from the effect of GA on W. trilobata, the applications of GA did not promote the adventitious roots of W. chinensis fast emerge and growth in the initial term, even significantly inhibited the adventitious root length and belowground biomass of W. chinensis. The root activities of W. chinensis also did not increased by GA application. We also test the effects of GA and PAC on the invasive weed Eupatorium catarium, Solidago canadensis and native weed Pterocypsela lacinata, GA application increased the shoot length of these three species, but not the biomass. PAC did not affect the root activities of the two invasive species but inhibit the native weed root activities.5) The isolated leaves experiment showed that the antifungal ability of W. trilobata is higher than that of W. chinensis. Gibberellin plays key role in the resistance to pathogen of W. trilobata. With the pathogen Fusarium oxysporum infected, leaf size, leaf number, shoot and biomass of seedling, which were treated with GA, were significant higher than that without treated with GA. In addition, the application of PAC were significant depress the seedling growth. The root activities of seedling with pathogen infected were significant lower than that without infection. However, the root activities of seedling with application of GA did not lower than CK treatment.These results showed that the main reasons of the failure of seedling recruitment and sexual reproduction of W. trilobata were the week light and dense litter layer under its populations, which inhibit seed germination and seedling growth. Gibberellin and litter could promote the clonal reproduction of W. trilobata. Gibberellin promoted the ramets fast growth, and increased the resistance to pathogen F. oxysporum. The litter of W. trilobata promoted its adventitious root growth, inhibited the other competitors’growth, and increased the inter-specific competition ability of W. trilobata, also inhibited the pathogen growth. This study explained the reasons of the failure of W. trilobata sexual reproduction, and it is important for the implications for biological invasion control. This study also showed the key role of gibberellin and litter in the clonal reproduction of W. trilobata. This will explain the invasion mechanism of W. trilobata in a new insight.