【作者】 柴民伟；

【导师】 石福臣；

【作者基本信息】 南开大学 ， 植物学， 2013， 博士

【摘要】 近年来,土壤重金属污染和盐渍化问题正成为国内外土壤环境治理和研究的热点。重金属污染不仅降低了土壤的肥力,而且影响植物生长发育,降低作物的产量和品质,最终通过食物链的富集作用对人类健康和环境安全造成危害。土壤的盐渍化不仅使土壤的可利用性降低,而且对植物生长造成伤害。土壤的盐渍化对植物的影响除了由中性盐(NaCl和Na2SO4等)引起的盐胁迫之外,还有由碱性盐(NaHCO3和Na2CO3等)引起的碱胁迫。与本土植物相比,具有入侵特性的外来植物具有较强的竞争力,能够耐受一系列恶劣的胁迫因子,包括干旱胁迫、温度胁迫、重金属胁迫和盐碱胁迫等。因此,对外来植物适应环境胁迫机制的深入研究,不仅可以揭示外来植物在盐渍土及污染土壤环境下的扩散机理,同时对防控入侵性外来植物的扩散发展,以及合理利用外来植物资源进行污染环境的生态修复,均具有重要的理论和实践意义。本文选择互花米草(Spartina alterniflora)和黄顶菊(Flaveria bidentis)两种典型外来植物为研究对象,其中对互花米草进行了以重金属污染为主的胁迫与适应性研究,对黄顶菊进行了不同发育阶段耐盐碱机理研究。本论文在考察了互花米草对天津滨海滩涂重金属积累的基础上,选择四种典型重金属(Cd, Pb, Cu和Zn)对互花米草进行胁迫试验,并研究了盐胁迫对互花米草的生理响应和对Cd积累的影响,最后探究了新型材料碳纳米管(CNTs)在互花米草修复重金属污染过程中所起的作用。结果如下：(1)互花米草降低了沉积物的容重和盐分,促进了沉积物对Cd, Cu和Pb的吸附。互花米草和光滩中的重金属含量均为：Zn> Cu> Pb> Cd。在互花米草和光滩的沉积物中,Cd的潜在生态危害系数最高,而重金属Zn、Cu和Pb属于轻微生态危害。互花米草和光滩中的重金属主要以残渣态的形式存在。就生物可利用态(酸溶态、还原态和氧化态)的重金属而言,光滩沉积物中的重金属含量小于互花米草群落。(2)互花米草须根对重金属胁迫的耐受性强于叶、茎和根茎。互花米草的重金属含量(Cd, Pb, Cu和Zn)均随着胁迫的增加而增长。Cd和Pb的积累量持续增加,而cu和zn的积累量呈现先增长后降低的趋势。重金属Cd,Pb和Cu主要积累在须根,而Zn主要积累在叶中。在Cd,Cu和Zn胁迫下,互花米草积累了大量脯氨酸和可溶性糖来进行渗透调节。草酸和柠檬酸是互花米草体内主要的有机酸。Cd胁迫下,草酸和柠檬酸可以指示须根吸收和积累Cd; Pb胁迫下,须根中的柠檬酸与Pb含量正相关；Cu胁迫下,叶和茎中的有机酸(草酸和柠檬酸)可能参与Cu积累和解毒；Zn胁迫下,叶中的草酸可能在Zn的积累过程中起作用。(3)在不同Cd胁迫下,NaCl对互花米草的生态响应和重金属积累的影响不同。NaCl促进了低Cd胁迫对互花米草的毒害,主要表现为植物生物量,植株高度和叶绿素a+b含量的降低。在低Cd胁迫下,NaCl增加了脯氨酸和ca2+的含量,而在高Cd胁迫下,出现了不变甚至降低的趋势。在低Cd胁迫下,NaCl通过增加CAT和POD的活性来降低Cd引起的氧化胁迫。在低和高Cd胁迫下,Cd含量随着NaCl浓度的增加而分别呈现升高降低的趋势。然而生物量的增加使Cd积累量随着NaCl浓度的增加呈现逐渐增长的趋势。在低Cd胁迫下,NaCl促进了Cd从地下向地上部分的转移系数,增强了互花米草对Cd的植物提取作用；而在高Cd胁迫下,NaCl降低了Cd的转移系数,促进了互花米草根部对Cd的固定作用。(4) CNTs对互花米草生态响应和Cd积累的影响取决于Cd胁迫的强度。在高Cd胁迫下,CNTs使受抑制的地上生物量,含水量和株高呈现恢复增长的趋势。CNTs增加了互花米草的K+和Ca2+含量,并降低了Na+/K+和Na+/Ca2+,在一定程度上缓解了Cd胁迫对互花米草的毒害作用。在CNTs和Cd联合作用下的脯氨酸含量显著低于单独的Cd胁迫处理。互花米草的根部积累了大量的Cd,在一定程度上保护了地上部分各种重要代谢活动的正常进行。在Cd胁迫下,CNTs增加了地上部分Cd积累量,这可能与CNTs对植株生长的生物稀释作用有关。在低Cd胁迫下,根部增加的Cd积累量主要是由于植物生长的稀释作用较强,而在高Cd胁迫下,根部Cd积累量降低,表明了植物生长的稀释作用较弱。为了研究黄顶菊在盐渍土上的入侵机理,本文模拟出25种不同的盐度和pH的混合盐对黄顶菊的种子进行处理,并选择中性盐NaCl和碱性盐Na2CO3对黄顶菊植株进行了梯度胁迫试验。结果发现：(1)黄顶菊种子的发芽率随着盐度和pH的增加而降低。经胁迫处理而未萌发的种子在复萌后大部分萌发,说明在盐渍土环境中,黄顶菊的一部分种子暂不萌发,等到雨水充足,盐碱胁迫减弱时复萌,这可能是黄顶菊避免植株在高盐碱胁迫下大量死亡的一种耐受机制。多元回归表明盐度是影响黄顶菊种子萌发的决定性因素,而其它胁迫因子作用较小；当种子萌发后,碱度(pH)开始作为影响幼苗生长的主要因素,而缓冲量对幼苗生长有一定的保护作用。(2)低盐度的中性盐NaCl对黄顶菊生长的影响不明显,但是随着盐度的增加,胁迫效应逐渐明显。碱性盐Na2CO3不仅使黄顶菊的日相对生长率显著降低,叶片电解质渗透率增大,而且增加了丙二醛、可溶性糖和游离脯氨酸含量。因此,与碱性盐渍土相比,黄顶菊对中性盐渍土具有较强的适应性。更多还原

【Abstract】 In recent years, soil heavy metal pollution and salinization have become the research hotspots in the field of environmental pollution control at home and abroad. Heavy metal pollution not only reduces the soil fertility, but also affects plant growth and crop yield, leading to the hazard on human health and environment security through food chains. Soil salinization reduces the soil availability, and causes harm to plant growth. Generally, the injury caused by soil salinization results from salt stress (NaCl and Na2SO4) and alkali stress (Na2CO3and NaHCO3). Compared to native plants, exotic plants have stronger competitiveness, and can endure a series of stress factors, including drought stress, temperature stress, heavy metal stress and salt-alkali stress. The further study of exotic plants to adapt to environmental stresses, can not only reveal the diffusion mechanism of exotic plants in saline and contaminated soil environment, but also has important theoretical and practical significance in prevention of exotic plants and rational utilization of exotic plants for ecological restoration. This paper has chosen exotic plant Spartina alterniflora and Flaveria bidentis as the research object to study the mechanism of adaptation on heavy metal and salt-alkali stresses.In the present study, the effect of S. alterniflora on sediment heavy metal accumulation was investigated in Tianjin coastal, China. Based on the results of the investigation, we studied the effects of heavy metals (Cd, Pb, Cu, and Zn) on plant growth and heavy metal accumulation in S. alterniflora, respectively. Furthermore, the physiological responses and Cd accumulations of S. alterniflora were also detected under salt stress. Finally, the function of carbon nanotubes on heavy metal phytoremediation of S. alterniflora was evaluated. The results were shown as follows:(1) In coastal zones of Tianjin, China, S. alterniflora decreased sediment bulk density and salinity, increased sediment adsorption of Cd, Cu and Pb compared to the mudflat. The heavy metal concentrations in Spartina and mudflat sediments were:Zn> Cu> Pb> Cd. In both Spartina and mudflat sediments, the potential ecological risk (PER) of Cd is higher than other heavy metals including Zn, Cu and Pb. Most of heavy metals exist in the residual form, which were not easy used by plants. In terms of heavy metal available for plants (acid-soluble, oxidable and reducible), heavy metal concentrations in mudflat were lower than Spartina sediments.(2) The heavy metal tolerance of fine roots was significantly higher than leaves, stems and rhizomes. In S. alterniflora, the heavy metal contents (Cd, Pb, Cu and Zn) increased with increasing heavy metal stresses. Continuous increases of Cd and Pb accumulation were also detected with increasing stresses. However, total amounts of Cu and Zn increased firstly, and then reduced. Cd, Pb and Cu were mainly accumulated in fine roots, with most of Zn located in leaves. S. alterniflora produced large amounts of free proline and soluble sugar to take part in osmotic adjustment under heavy metal stresses. Oxalic and citric acids were the two most abundant organic acids in S. alterniflora. Under Cd stress, oxalic and citric acids acted as indicator of Cd uptake and accumulation in fine roots. Under Pb stress, citric acid was positively related with Pb accumulation in fine roots. Under Cu stress, oxalic and citric acids may take part in Cu accumulation in leaves and stems. Under Zn stress, oxalic acid may function in Zn accumulation in leaves.(3) Under different Cd stresses, the effects of NaCl may be varied on physiological responses and heavy metal accumulation. Under moderate Cd stress, NaCl improved the harm of Cd on plant, which can be determined by lower biomass, plant height and chlorophyll a+b contents. Under moderate Cd stress, NaCl increased proline and Ca2+contents, different from unchanged trends under severe Cd stress. Further, NaCl alleviated the oxidative stress under moderate Cd stress by improving the activities of CAT and POD. With NaCl addition, Cd contents in S. alterniflora increased and reduced under moderate and severe Cd stress, respectively. However, biological dilution caused by improved biomass led to increases of total Cd accumulation with increasing NaCl concentration. Under moderate Cd stress, NaCl increased Cd translocation factor (TF); while, phytostabilization of Cd may be probable under severe Cd stress due to the reduced TF.(4) In S. alterniflora, the effects of CNTs on physiological responses and Cd accumulation depend on the degree of Cd stress. CNTs alleviated higher Cd stress because of restored shoot growth reduction, water content and plant height. CNTs alleviated the detrimental effects of Cd stress by increasing K+and Ca2+contents, while reducing Na+/K+and Na+/Ca2+ratios. The proline contents in treatment with only Cd were higher than treatments with both Cd and CNTs, indicating that CNTs reduce production of organic solutes under Cd stress. There were higher Cd accumulation in roots than shoots, and both were improved by CNTs, except for reduction in roots under higher Cd stress. CNTs did not affect the inhibition of Cd on growth of S. alterniflora, but improved Cd accumulation under lower Cd stress. However, under higher Cd stress, CNTs resumed the inhibited plant growth, promoted and reduced the Cd amounts in shoots and roots, respectively.In order to understand the invasion mechanism F. bidentis in saline soil,25different salinity and pH conditions were simulated and seed germination were determined. On the other hand, we study the effects of neutral salt NaCl and alkaline salt Na2CO3on growth of F. bidentis, which is helpful to illustrate the salt-alkali resistance of F. bidentis in the vegetative growth phase. The results showed that:(1) The germination rates of seeds reduced with increasing salinity and pH. Un-germinated seeds germinated well after being transferred to distilled water, demonstrating that parts of F. bidentis seeds are well adapted to salt-alkali stresses due to high capacity for germination recovery. Therefore, the ungerminated seeds under high salt-alkali stresses may be a tolerance mechanism which avoids massive death of plant under severe saline condition. Stepwise regression analysis showed that salinity is the dominant factor affecting seed germination; after seed germination, alkalinity (pH) acted as the main factor which impacted seedling growth. The buffer capacity has some protective effect on seedling growth.(2) The influence of lower NaCl stress on plant growth is not significant, and the inhibitory effect becomes significant with increasing NaCl concentration. Na2CO3reduced relative growth rate, improved leaf electrolyte leakage rate, and increased contents of MDA, proline and soluble sugar. Thus, there were stronger resistance and adaptability of F. bidentis to neutral saline soil compared to alkaline saline soil.更多还原