镉和模拟酸雨胁迫对苦楝幼苗镉含量及叶片抗氧化系统的影响

为探讨苦楝在重金属Cd和酸雨的单一及复合胁迫下的生理响应特征,采用人工配置土壤盆栽试验,研究不同浓度Cd(0、30、60、90、120、150、180 mg·kg-1)和3个梯度模拟酸雨(pH值5.6、4.5、3.5)单一及复合处理对苦楝幼苗生物量、Cd含量及叶片保护性酶[超氧化物歧化酶(SOD)、过氧化物酶(POD)和过氧化氢酶(CAT)]活性和抗坏血酸-谷胱甘肽循环(AsA-GSH)的影响。结果表明,除低浓度Cd(≤30 mg·kg-1)单一及其与pH值4.5酸雨复合处理对幼苗地上部、地下部生物量有促进作用外,其他处理均表现出抑制作用,其中复合处理对苦楝幼苗的抑制作用更明显,表现为叠加效应;单一Cd处理时,随着Cd浓度的增加,幼苗根、茎、叶中Cd含量逐渐升高,且根系大于茎叶,复合处理抑制了植物对Cd的积累,对叶片的抑制作用最强;Cd和酸雨单一及复合处理下叶片SOD、CAT和POD活性均有所增加,分别在60 mg·kg-1 Cd、pH值5.6,60 mg·kg-1 Cd、pH值4.5和90 mg·kg-1Cd、pH值4.5时出现阈值;在AsA-GSH循环中,单一Cd处理下,AsA、GSH含量和抗坏血酸过氧化物酶(APX)、谷胱甘肽还原酶(GR)活性均随着Cd浓度的增加呈先上升后下降的趋势,单一酸雨处理对上述4个指标的影响不尽一致,而复合处理下上述指标在Cd浓度≤60 mg·kg-1、pH值≥4.5时均能保持较高值,且随着胁迫程度的加深均出现了阈值。综上所述,苦楝对重金属Cd和酸雨胁迫具有一定的耐性,可在Cd浓度≤60 mg·kg-1和pH值≥4.5的酸雨双重污染区域正常生长。本研究结果为土壤Cd污染的酸雨区域的修复植物筛选提供了理论基础和参考依据。

Effects of Simulated Acid Rain and Cadmium Stress on Cd Content and Antioxidant System of Melia azedarach L. Seedlings

In order to investigate the physiological responses of Melia azedarach L. to Cd and acid rain under single and combined stresses,effects of the single and combined treatment with the different concentrations of Cd²⁺(0,30,60,90,120,150 and 180 mg·kg^-1) and three types of simulated acid rain(pH value 5.6,4.5 and 3.5) on the seedling aboveground and belowground biomass,contention of Cd, the activity of protective enzymes(SOD,POD and CAT)as well as AsA-GSH circulatory system Melia azedarach seedings were studied by pot experiments. The results showed that under Cd and acid rain single or combined treatments, the biomass of aboveground and underground was lower than that of CK except for low concentration of Cd (≤30 mg·kg^-1) and combined with pH value 4.5 acid rain. The combined treatments showed more obvious influence than single treatments.In single Cd treatment, the contents of Cd in roots,stems and leaves increased with the increase of Cd concentrations,the roots was larger than that of stems and leaves,combined treatment inhibited the accumulation of plant to Cd, and the inhibitory effect on leaves was the strongest. The activities of SOD,CAT and POD were stimulated by single and compound treatment of Cd and acid rain,which thresholds appeared at 60 mg·kg^-1 Cd and pH value 5.6 treatment,60 mg·kg^-1Cd and pH value 4.5 treatment,90 mg·kg^-1Cd and pH value 4.5 respectively. In the AsA-GSH, the AsA,GSH contents and APX,GR activities increased first and then decreased with the increase of single Cd stress, but the four showed different trends with the change of acid rain. However,under the combined treatment of Cd≤60 mg·kg^-1 and pH≥4.5,the four substances maintained high content and activity,and showed a threshold with the deepening stress. In summary, Melia azedarach had certain tolerance to Cd and acid rain, and can normally grow in the the double polluted area of Cd concentration ≤60 mg·kg^-1and acid rain pH ≥4.5.The study provides a theoretical basis and reference for screening plants for acid rain area contaminated by cadmium.