Abstract: Spartina alterniflora is a rhizomatous perennial, native to the Atlantic and Gulf coasts of North America, occurring from Quebec and Newfoundland to Florida and Texas. In China, S. alterniflora was introduced to stabilize shorelines and increase vegetative cover in 1979, and now flourished in many inter-tidal zones of gulfs and estuaries with its spread. As a consequence of rapid globalization, greatly increased emphasis is placed on research of the ecology of invasive plants. S. alterniflora was introduced into Haihe estuary in 1998, it has gradually occupied a large area of the indigenous plant Phragmites communis zone, and P. communis was squeezed out into a higher plot. In this study, the POD, CAT, SOD activities, the contents of free proline and soluble sugar, and the relative permeability of plasma membrane in different organs between the two species were measured and compared. The experiments were performed during the growing season in 2005 at Haihe delta wetland, in E 117°45′, N 39°03′. The main experimental results were as follows:The SOD, POD, CAT activities, free proline and soluble sugar contents of S. alterniflora were lower than those of P. communis; Free proline and soluble sugar were two compatible substances and played important roles in keeping osmotic balance in both S. alterniflora and P. communis; Relative plasma membrane permeability tended to remain stable in both species, and maintain at a higher value in S. alterniflora than that in P. communis as a whole. These results could be helpful in explaining the physiological and ecological mechanisms of S. alterniflora with respect to its strong competitive ability.

Key words: Spartina alterniflora, Phragmites communis, defense enzymes, free proline, soluble sugar, relative permeability of plasma membrane