中文摘要：

根据中国东北盐碱土壤特点,将4种盐NaCl、NaHCO3、Na2SO4和Na2CO3按不同比例混合,模拟出25种盐度和pH值各不相同的复杂盐碱条件（盐浓度为50-250mmol/L,pH值为7.12-10.46）,并对向日葵苗进行盐碱混合胁迫处理,研究了向日葵超氧化物歧化酶（SOD）、过氧化氢酶（CAT）和过氧化物酶（POD）酶等抗氧化酶系统和丙二醛（MDA）的盐碱协同胁迫效应.结果表明,向日葵抗氧化物酶活性强弱同时与盐度和碱度密切相关,3种抗氧化物酶活性对于盐浓度的反应相似,均为其含量随着盐浓度的升高开始逐渐升高然后下降,而对于pH的影响,不同酶反应结果不同.即随着pH值升高,SOD酶活性和CAT酶活性降低,而POD酶活性反应则是随着pH值升高活性也升高.双向方差分析（ANOVA）结果表明：盐碱效应对于3种酶活力的影响是显著的.其中,盐效应对POD和SOD活性的影响比pH值的影响大,而pH值对CAT活性的影响效应比盐效应大.除SOD外,盐碱效应的交互作用显著（P〈0.001）.抗氧化酶系统和MDA含量两者间相关性和逐步回归分析表明,3种酶对MDA的影响效应随其强度不同呈现显著不同.其中SOD是1个主导因子,CAT处于次位,而POD的影响不大,甚至可以忽略.

英文摘要：

Based on the characteristics of salt-alkalinized soil in northeastern China, twenty-five kinds of saltalkaline conditions with different salinities and pH were simulated by mixing NaCl, NaHCO3, Na2 SO4, and Na2 CO3 , in various proportions and applied to sunflower （ Helianthus annuus L. ） seedlings to investigate the coordinative effects of salt and alkali stresses on its antioxidant enzyme system. The soil was conditioned with a salt concentration range between 50 to 250 mmol/L and pH values from 7.12 to 10.46. Several physiological indexes of stressed seedlings were measured, including the activities of superoxide dismutase （SOD）, catalase （CAT）, and peroxidase （POD）, as well as the content of malondialdehyde （MDA）. The results showed that the responses of the antioxidant enzyme system in sunflowers were influenced by salinity and alkalinity, which all. three antioxidant enzymes exhibited a rise-drop pattern as salinity increased, whereas their responses to alkalinity appeared to be diverse： decreased for SOD and CAT, and increase for POD along when increasing alkalinity. A two-way analysis of variance （ANOVA） showed that the effects of salinity and alkalinity on the activities of the three enzymes were significant （ P 〈 0.001 ）. The effect of salinity on POD and SOD was greater than that of alkalinity, whereas the effect of alkalinity on CAT was greater than that of salinity. The interrelation of salinity and alkalinity on each antioxidant enzyme was significant （ P 〈 0.001 ） except for SOD. The correlation and stepwise regression analyses between the activity of the antioxidant enzyme system and the MDA content were significant to different extend, SOD was a dominant factor, and POD was neglectable.