Under stress of Na 2CO 3,catalase (CAT) activities of Puccinellia tenuiflora seedlings increase as the stress time goes on,that has significant positive relationship with the stress intensity.Superoxide dismutase (SOD) activities of P.tenuiflora seedlings increase as the stress time increase and along with the stress intensity strengthen to a certain intensity (3.0% Na 2CO 3) which decreased.Changes of peroxidase (POD) activities of P.tenuiflora seedlings is same as that of SOD activity,Howe...