Comparison Of Ecological Adaptability Of Different Populations Of The Crofton Weed(Ageratina Adenophora Spreng)

Ageratina adenophora Sprengel is one of the worst invasive plant species in China. Investigating the adaptation mechanism to different habitats of A. adenophora could help to understand invasive mechanism and provide scientific basis for control of this weed. Ten populations of A. adenophora located at different latitude (N21°41'47"-26°53'02"N) and altitude (678m-2420m) in Yunnan were selected to study the germination of seed under different temperature grads (15℃,20℃,25℃,30℃,35℃). In addition, seedlings of five different populations of this weed were reciprocally transplanted into six different sites in Yunnan, using method of reciprocal transplant. The survival, plant height, branch number, individual biomass, root-shoot ratio, flower number, seed number of seedlings and germination of seeds produced by seedlings transplanted into each site were measured during the experiment period from Jun 2007 to May 2008. The results were as following:1. The optical temperature for seed germination was about 25℃for every population. The germination capacity of seed increases with increase of temperature within the range of 15℃to 25℃. There were no close relationships between seed germination percentages and the site conditions of seed populations under each temperature condition. Seed germination index decreased with increase of latitude and altitude of population site, while mean time to germination extended with increase of latitude and altitude of population site.2. All seedlings of A. adenophora transplanted into four sites (Menglun, Dadugang, Kunming and Hongyan) survived till the end of the experiment, except the seedlings in Jianchuan and Lijiang died due to low temperature and frost in winter during the period of the experiment, explaining the wider tolerance range to environmental changes of A. adenophora.3. There was significant effect of transplant site on growth and reproduction traits of seedlings of A. adenophora (p<0.001). For each population, plant height, branch number, biomass, flower number and seed number of the weed decreased with increase of latitude and altitude of transplant sites, the differences in growth and reproduction traits were significant between the sites (p<0.001). All traits mationed above were postively correlated with annual average temperature of transplant site (p<0.001). Root-shoot ratio of the weed decreased with increase of latitude and altitude of transplant site. Root-shoot ratio of each population were negatively correlated with annual average temperature of transplant site (p<0.001). These results show that each population of this weed has high phenotypic plasticity, could showed strong plasticity to variations in environmental conditions.4. The interaction effects of population and site on the above mentioned traits were not significant (p>0.05), except the number of seed. Within each site, the significant differences in plant height, branch number, individual biomass, flower number of the weed were not found among different populations (p>0.05). There was no significant superiority observed in terms of growth ability and reproductive ability in local population. The evidence for local adaptation of A. adenophora populations was not found in the study.5. There was significant effect of transplant site on phonological rhythm of seedlings of A. adenophora. The stage of leaf exchange of the seedlings began in the end of December,2007 in both Kunming and Hongyan sites, while that were in the end of February and middle of March,2008 in Menglun and Dadugang site. The flower buds of A. adenophora were visible in early Jan. and flowering began in late Feb. in Dadugang, Kunming and Hongyan sites. In Menglun site, the times of sqaring and flowering were delayed to the middle of Feb., the middle of March,2008. However, there were no significant differences between phonological rhythms of different populations of A. adenophora within each of the four sites.6. Based on the above results, this study suggested that the high phenotypic plasticity and wider ecological adaptability would play a more important role than local adaptation in the invasion of A.adenophora in southwest of China up to now.