| Ambrosia Linn.is a serious threat to human health because of its abundant allergenic pollen release. Ambrosia artemisiifolia L. and Ambrosia trifida L., two annual invasive plants in China, not only invade a broad range of open disturbed areas, such as wastelands, roadsides, and riverbanks, but also field crops. The mechanistic of the invasion of Ambrosia Linn. is still unknown. In this study, the germination traits, Arbuscular Mycorrhiza fungi (AMF) communities composition and diversity of Ambrosia species were investigated The main results showed as follows:1. Germination of Ambrosia artemisiifolia L. seeds collected from Mudanjiang, Nanjing, and Nanchang occurred over a range of constant temperatures from 5 to 40℃.Seed germinated equally well in constant light/darkness and continuous darkness. Germination exceeds 48% in solutions with pH4 tol2. Maximum germination (average 98.2%) was observed in distilled water at pH 5.57. Germination was greatly reduced in solutions with osmotic potentials below -0.8Mpa (average 10.5% at -1.2Mpa); no germination was observed at -1.6Mpa. Average of germination was greater than 69% at less than 200mmol·L-1 NaCl and 8% at 400mmol·L-1 NaCl. Percentage emergence was greater than 75% at burial depths of 1 to 4 cm, and no seedling emerged from a soil depth at 8cm.2. Germination of Ambrosia trifida L. seeds collected from Shenyang, Beijing, and Nanchang occurred over a range of constant temperatures from 5 to 35℃. Seed germinated in constant light/darkness and continuous darkness. Seed germinated over a broad range of pH (4 to 12). Maximum germination (average 66.1%) was observed in distilled water. Germination was greatly reduced in solutions with osmotic potentials below -0.4Mpa (average 12.8% at -0.8Mpa); no germination was observed at -1.2Mpa. Average of germination was greater than 51% at less than 100mmol·L-1 NaCl and 13.2% at 300mmol·L-1 NaCl. Percentage emergence was greater than 71% at burial depths of 1 to 4 cm, and no seedling emerged from a soil depth at 16cm.Our results indicate that Ambrosia spp. is capable of germinating in a variety of climatic and edaphic conditions. Ambrosia artemisiifolia L.seeds collected from Mudanjiang, Nanjing, and Nanchang have the same germination traits. Ambrosia trifida L. seeds collected from Shenyang, Beijing, and Nanchang have the same germination traits. They have the same optimum temperature, the same range of pH, osmotic potential, salinity concentration and planting depth. It explains that Ambrosia spp. has a broad distribution range. The broad range and the high germination is one of the reasons that the rapid spread of this invasive species.3. We used PCR-DGGE method to estimate the molecular diversity of AMF in roots of Ambrosia spp. and found the AMF diversity was low. Total of ten AMF species which belong to the genus of Glomus were detected in all samples, these AMF species including: G.sp1,G.sp2,G.sp3,G.sp4,G.sp5,G.sp6,G.sp7,G.sp8,G.sp9,G. viscosum. Two of these AMF species is cultured, including: Glomus viscosum and Glomus sp. MUCL(G.sp6).4. We estimate the molecular diversity of AMF in the roots of invasive weeds, Ambrosia artemisiifolia L and Ambrosia trifida L.. Communities composition of AMF in different plant species had some difference. Seven clusters can be recognized, five clusters containing roots of Ambrosia artemisiifolia L, and two clusters Ambrosia trifida L. . Sequence G7 was exclusively characteristic of the Ambrosia trifida L..5. Ambrosia artemisiifolia L or Ambrosia trifida L. growing on the different sites showed negligible differences in their root AM fungal community composition. However, AMF community composition of Ambrosia trifida L. from Shenyang appear in a well-defined cluster.Our results show that Ambrosia artemisiifolia L and Ambrosia trifida L. utilized successfully local AMF ,is one of the mechanisms of plant establishment. The difference of utilization AMF could induce difference invasive ability of Ambrosia artemisiifolia L and Ambrosia trifida L..
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