| Spartina alterniflora has become an important exotic invasive species and expanded rapidly since it was introduced to the eastern coasts of China. In this study, landward sampling sites along an intertidal zone in Xingyanggang(S. alterniflora patch(SAP), S. alterniflora flat infra-edge(SAFI), S. alterniflora flat 2003 (SAF03), S. alterniflora flat 1989(SAF89)) were arranged and (1) the S. alterniflora seed characteristics were investigated to study the expansion ability in each sampling site; (2) transient soil seed bank and seed preservation were measured; (3) the contribution of sexual reproduction in S. alterniflora population sustainability and expansion were discussed; (4) the seedling and ramet growth strategies choice in different habitat during the expansion of S. alterniflora were explored. (5) Using cultivated Spartina alterniflora in laboratory as experimental metarial to decide test the effect on photosynthetic pigment contents and rapid light response curves of S. alterniflora. The results showed that:1. Survival rate of cultivated S. alterniflora ramets at Mudflat was 7.8%, which was significantly lower than the others except SS (p<0.01). The survival rate at SAP, SAFI, SAF03, SAF89, SS and Grass flat was 88.9%,77.8%,60.0%,81.1%,0 and 66.6% respectively; Influenced by physical erosion of seawater and waves, tidal flooding and soil water content, the seed germination percentage in different sampling sites of experimental system was low; and SAFI has highest percentage of 17.8%. Although the ramet survival rate is greater than seedling survival rate, the probability of asexual reproduction should be much smaller than the probability of sexual reproduction in quantity and diffusion under natural conditions.2. Ramets were successfully settled and become fruited, while the seedlings, in addition to SAP and SS seedlings all died, only Mudflat and SAFI produced fruit. November 11, The Clonal number come to 21.7 at Mudflat,25.5 at SAP,23.0 at SAFI,6.8 at SAF03,9.0 at SAF89 and 4.1 tillers per ramat at Grass flat respectively. Except tiller number of seedlings reached 14.0 at Mudflat, others did not reached 1.0. S. alterniflora biomass of ramet was significantly greater than seedling's in different sampling sites.3. The morphological characteristics of ramets in the study area at SAP, SAFI and SAF89 sampling sites in the S. alterniflora height, leaf length, leaf number, leaf width and leaf thickness were higher rather than forefront of offshore. Seedling growth at SAFI was well, while others were small or dead. Above-ground biomass allocation of two reproductive mode decreased toward sea and toward land, respectively, while the underground biomass allocation showed the opposite situation.4. In November 2009, the seed production was significantly different (p<0.01) among sampling sites on the order as SAP> SAF03> SAFI> SAF89, which is positively correlated with the setting rate, longer spike length and seed number per spike. By April, the transient soil seed bank was significantly different (p<0.01) among sampling sites as 673.7/m2 at SAP,2328.7/m2 at SAFI,5948.8/m2 at SAF03 and 3990.4/m2 at SAF89, respectively; and the seed preservation rates was 0.5%at SAP,3.9%at SAFI,6.9%at SAF03 and 15.8%at SAF89, respectively. By July, the seedling numbers was 72/m2 at SAP,5/m2 at SAFI,0 at SAF03 and SAF89. The water content of topsoil and light attenuation within populations affected seedling growth vitally.5. There was significant difference in various waterlogging depth-0 cm,10 cm,20 cm(p<0.01). Long-time can reduce tiller and biomass of S. alterniflora. There was some difference in various waterlogging time(p<0.01) and tiller and biomass of S. alterniflora will reduced with waterlogging time increasing and S. alterniflora were all dead by 20 cm and 24 h waterlogging on the first 40 days. Longer flooding time increased chlorophyll content of S. alterniflora under 0 cm flooding condition; chlorophyll content was higher than others at 4 h/d and 6 h/d under 10 cm and 20 cm flooding condition; With the same flooding time duration, chlorophyll a content and chlorophyll b content increased with increasing water depth during the flooding period of 4 h/d and 6 h/d; The carotenoid content decreased when flooding duration increased under 0 cm flooding condition. The carotenoid content at 4 h/d and 6 h/d were 34%and 38%higher than at 2 h/d under 20 cm flooding condition respectively. The electron transport rate and the minimum saturation light intensity level of S. alterniflora decreased with longer flooding duration and higher water depth. |
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