Physiological and ecological responses of hetan and chaotan Phragmites australis to salt stress

Abstract

Characterizing the different physiological and ecological responses of Phragmites australis from two habitats in the Yellow River delta to salt stress can provide important theoretical support for the selection of P. australis types for the ecological restoration of degraded coastal wetlands. The Na+ content, photosynthetic parameters, H2O2 content, antioxidant enzyme activity, malondialdehyde content, and proline content of leaves from hetan（low-salt habitat, riverside） and chaotan（high-salt habitat, high marsh） P. australis grown under salt stress conditions（300 mmol/L NaCl） were compared, along with the Na+ flux of the root growth area. Salt stress significantly increased the Na+ content in the hetan leaves but had no significant effect on that of the chaotan leaves. Furthermore, non-invasive micro-test technology（NMT） revealed greater Na+ efflux in the chaotan plants(（1982.05±122.74） pmol cm-2 s-1 vs.（87.93±12.94） pmol cm-2 s-1, P<0.01)than in the hetan plants(（1574.16±458.90） pmol cm-2 s-1 vs.（-126.88±23.01） pmol cm-2 s-1, P<0.01), which could be attributed to the need for chaotan P. australis to effectively regulate intracellular ion balance. In addition, the photosynthetic rate of the chaotan plants(（16.36±1.09） μmol m-2 s-1 vs.（22.79±0.67） μmol m-2 s-1, P<0.01) was significantly greater than that of the hetan plants(（12.71±0.97） μmol m-2 s-1 vs.（23.81±0.55） μmol m-2 s-1, P<0.01)after 7 d of salt treatment. Salt stress induced significant increases in the H2O2, malondialdehyde, and proline contents of leaves from both P. australis types, as well as in the activity of antioxidant enzymes. Moreover, the activity of glutathione reductase（GR）in chaotan P. australis was increased significantly（（6.90±1.73） U/mgprot vs.（3.54±0.54） U/mgprot, P<0.05）. These results indicate that chaotan P. australis is more adaptable to salt stress than hetan P. australis, as indicated by the greater Na+ efflux of its roots, greater proline content, and greater antioxidant enzyme activity, which promote salt-stress tolerance. Therefore, in the ecological restoration of degraded coastal wetlands in the Yellow River delta, P. australis from the high marsh should be selected as the material for vegetation restoration