Seed dispersal is one of modes with which Spartina alterniflora population colonized new habitats (Richards et al., 2004; Davis, 2005). The maximal number of grain per inflorescence was 665 (Fang et al., 2004). After shedding at autumn, seeds of S. alterniflora keep dormancy to spring of second year and the maximal germination rate is over 90% (Qin et al., 1985). Dormancy mechanism will be favor of seed survival through the severe winter, and companying with temperature rise and rainfall increase, seeds are germinating. The strategy could increase the survival of seedling. In hypoxia condition, the strategy which coleoptile and hypocotyl elongate quickly will accelerates seedling of S. alterniflora coming up out of land. Moreover, oxygen produced by the photosynthesis of green embryo in coleoptile could stimulate the root growth of the species (Wijte & Gallagher, 1996a, 1996b).
S. alterniflora could expand the populations using rhizome or vegetative fragment dispersal besides sexual reproduction (Daehler & Strong, 1994). The population maintenance and expansion was depending fully vegetative reproduction in New Zealand (Partridge, 1987). In foreland of invasive populations, the isolated "pioneer" clones joint into continuous swards through vegetative reproduction (Davis et al., 2004a). However, the vegetative reproduction and clonal expanding rate vary with habitats. The length of rhizome and capability of vegetative reproduction varied with the organic content in substrate, and 14 new shoots were produced by each seedling in higher organic content substrate (Padgett & Brown, 1999). In large bare patches in field, S. alterniflora seedlings grew non-directionally, and produced as many as 36 tillers in one growing season (Metcalfe et al., 1986). Lateral growth rates of individual S. alterniflora patches increased linearly at 79.3 cm cm yr-1 and recruitment of new clonal patches had been episodic and increasing in frequency (Feist & Simenstad, 2000). Proffitt et al. (2003) reported that the rate of clonal expansion in diameter was 3.1 m per year. The number of new shoots produced by a ramet, which planted in Luoyuan County, Fujian Province of China, was more than one thousand in one year. The rate of clonal expansion in diameter was more than 2 m and the diameter of clone was more than 19 m after 4 years (Chung et al., 2004). In a word, S. alterniflora not only produces a great deal of seeds and colonizes new habitats, but also expands its population through rapidly clonal reproduction. S. alterniflora population practise local movement ( "flow" diffusion) with clonal reproduction and long-distance jump with seeds (Hastings et al., 2005).
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