Effects Of Crofton Weed Invasion On Plant Diversity At Different Elevations And Its Seed Germination Traits

Crofton weed, Ageratina adenophora (Sprengel) R. King & H. Robinson, occurred originally from Mexico to Costa Rica in the southern America. It is an invasive species and it invaded from the border of China and Burma in 1940s. It is widely distributed in Southwest China, spreads very fast and thus it gets the focus of all the society. It adjusted to many habitats, expended soil nutrient and reduced the diversity of community. Insects and livestock refused to eat it. It made great loss to the agriculture and economy. The study included characters of seed germination of crofton weed, the influence of invasive place biodiversity at different elevations and the dynamics of crofton weed. The paper was supported by National Basic Research Program of China (2009CB119205) and the main results were as follows:1 Effects of environmental factors on seed germination of crofton weed at different elevationsThe seed traits and weight from higher elevation is bigger than the lower's. The Germination Index (GI) and Germination Capacity (GC) of the seed in 2100 m is the biggest. The seeds can germinate from 10℃to 35℃, GC and GI are biggest at 15℃. GC and GI are biggest at 50 mM NaCl solution, there is almost no germination at 300 mM NaCl solution and -0.8 MPa PEG6000 solution. When the concentration of NaCl PEG6000 solution is higher, the seed germination is lower.2 Effects of crofton weed invasion on plant diversityInvaded natural forests at 4 elevations in the southwest of Sichuan province were surveyed. The richness of 2100 m invasive place is highest while the richness of 1400m is lowest. The diversity characteristics in different elevations declined at dry season, and it began to rise at rainy season. The diversity characteristics in low richness rose slowly. The soil of invaded place was acidic, which was conductive to seeds germination. The invasion of crofton weed may decline the biodiversity to become single steady area.3 Annual dynamics of crofton weed at different elevationsThe biomass of crofton weed at low elevations is heavier than the high's. Crofton weed at low elevation is more competitive. The contents of nitrogen, phosphorus and kalium of crofton weed decreased in blossom period, which indicated that the weed changed vegetative growth to reproductive growth. The biomass and height of crofton weed in different elevations declined at dry season, and began to rise at rainy season. The biodiversity was low at 1400 m while crofton weed grew up fast. It showed the reduction of biodiversity will decline the ability of local community in refusing the invasion and spread of invasive species.