ANALYSIS ON THE FLUX OF SOIL SEED BANK AND THE SEEDLING MORTALITY IN THE COMMUNITIES OF TWO SPECIES OF SU AEDA IN THE SONGNEN PLAIN IN CHINA Cloning of a Vacuolar H+-pyrophosphatase Gene from the Halophyte Suaeda corniculata whose Heterologous Overexpression Improves Salt, Saline-alkali and Drought Tolerance in Arabidopsis Adaptive strategies of dimorphic seeds of the desert halophyte Suaeda corniculata in saline habitat