| The crofton weed, Ageratina adenophora (Sprengel) R. King & H. Robinson, is a noxious invasive weed worldwide. Belonging to Compositae, it is a kind of half shrubs and bunch type herbaceous plants. In China, the weed is mainly distributed in southwest. Once invasion, it could establish dominant community easily, push out native plants, and thus bring huge losses for the ecological environment and local agriculture, forestry, animal husbandry. In the thesis, field investigation and indoor assay methods were applied to study the plant community characteristics in different habitats after the invasion of crofton weed. Besides, the seed morphological and traits difference of the weed were comparatively analyzed. The outcome will provide some basic theoretical information for clarifying mutual relationship between the invasion of the weed and its spatial and temporal dynamics and understanding invasion mechanism of the weed and its potential distribution areas. The study was supported by National Basic Research Program of China (2009CB119205) and the main results were as follows:(1) Characters including seed length, width, weight and vigor of Ageratina adenophora in different habitats were assayed and comparatively described. The results indicate that the seed vigor, length, width and weight of Ageratina adenophora in forestry ecotone are all significantly higher than the counterparts in other habitats, and the above indexes are lowest in natural forests.(2) The seed germination characteristics of Ageratina adenophora under different temperatures, salts and water stress were comparatively studied. The results showed seed germination capacity was negatively correlated with temperature. The seeds germination capacity is highest at 10℃and 15℃, reached 75.6 to 95.2 percent; with the rise of temperature the seed germination capacity declined. It is disadvantageous for germination of the seed at 35℃. A negative relationship between seed germination rate and salt concentration existed. At 50 mM treatment, the seed has highest germination rates among different habitats, significantly different from other treatments. At-0.4 MPa treatment, the seed has highest germination ability among different habitats. However, with the rise of water stress, the seeds germination declined with seed germination lowest in-0.8 MPa.(3) The dynamics of plant community diversity in different habitats after Ageratina adenophora invasion was investigated. The result showed at August and September the species richness reached highest in different habitats, while the richness reached lowest at January and April. Richness of abandoned land, forestry ecotone and natural forests reach-ed peak at August and at September of roadside and man-made forest. The dynamics of total indivi-dual number expressed similar trend in different habitats:peak in July to Octo-ber while lowest in January to May. Among those habitats, the total individual number of plant is highest in abandoned land; second is forestry ecotone, and then is manmade forest, roadside and natural forests.(4) The density dynamics of crofton weed seedling in different habitats was investig-ated. The unearthed time of Ageratina adenophora seedling mainly focused on June and July; the seedling number is lowest in January and March, significantly different from the values in other months.(5) The density dynamics of soil nutrient (available nitrogen, phosphorus and kalium) in different habitats was assayed. The result show that the contents of soil available nitrog-en and phosphorus increased during growth stages of crofton weed while the content of soil available potassium decreased. |
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