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To evaluate genotypic difference in antioxidative ability and salt tolerance in poplars, the authors investigated the effects of increasing content of soil NaCl on salt concentration in leaves, superoxide dismutase (SOD) and peroxidase (POD) activities, malondialdehyde (MDA) content, and membrane permeability (MP) in Populus euphratica Oliv., P. popularis "35-44," and P. × euramericana cv. I-214 (hereafter abbreviated as P. cv. I-214). Na + and Cl − concentrations in leaves of P. popularis increased markedly over the increase of the duration of exposure to salinity, and culminated after 28 days of salt stress. SOD and POD activities declined correspondingly, followed by significant increases of MDA and MP, and leaf injury was finally observed. Compared with P. popularis, leaf Na + and Cl − in P. cv. I-214 exhibited a trend similar to P. popularis, but a lower salt-induced increase of MDA and permeability was observed and lighter leaf necrosis occurred. In contrast to P. popularis and P. cv. I-214, SOD and POD activities in P. euphratica leaves increased rapidly at the beginning of salt stress with a light soil NaCl concentration of 58.5 mmol/L. Furthermore, salt ion concentration, MDA content, and MP in P. euphratica leaves did not increase significantly during 28 days of increasing salt stress. Therefore, the increase in MP in P. popularis and P. cv. I-214 had a close relationship with a salt buildup in leaves under increasing salt stress. Salt-induced declines of SOD and POD activities might accelerate lipid peroxide and consequently resulted in ion leakage. P. euphratica rapidly activated antioxidant enzymes after the onset of salt stress, which might reduce the accumulation of reactive oxygen species and the subsequent acceleration of lipid peroxide. P. euphratica leaves exhibited a higher capacity to exclude salt in a longer period of increasing salinity, thus limited salt-induced lipid peroxide and MP, which contributed to membrane integrity maintenance and salt tolerance of P. euphratica.

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