【作者】 林长存；

【导师】 祝廷成； 王德利；

【作者基本信息】 东北师范大学 ， 生态学， 2009， 博士

【摘要】 工业“三废”和机动车尾气的排放、污水灌溉及农药、除草剂和化肥的使用,污染了土壤,水体和大气,其中土壤中的重金属铅污染更为严重。重金属铅在植物根、茎、叶及籽粒中的大量积累,不仅影响植物的生长和发育,而且会进入食物链,危及人类的健康。存在于土壤中的重金属铅难以被微生物分解和转化,对动植物和人类的危害具有隐蔽性,长期性和不可逆性等特点。目前采用的物理化学方法修复重金属污染土壤,费用昂贵,破坏环境,容易造成二次污染,且往往并不能达到真正清除重金属的目的。近十年出现的植物修复技术在不破坏环境的条件下使土壤重金属得以清除,是一种绿色环保技术。植物修复过程中重金属铅迁移特性在很大程度上取决于土壤的化学特性,其在介质中的存在形态是衡量重金属铅环境效应的关键参量。近年来,EDTA和N、P、K肥等基质在重金属铅污染土地上的植被重建中有着重要的作用,但是,EDTA的添加方式和N、P、K肥如何以及多大程度上影响重金属铅的移动性和植物的重金属吸收研究较少。我们采用中国北方常见的几种植物——菠菜(Spinacia oleracea)、马齿苋(Portulaca oleracea)、苣荬菜(Sonchus arvensis)、向日葵(Helianthus annuus)作为实验材料,通过室内盆栽的实验,运用生理生化等技术分别从个体和器官水平上研究几种植物耐铅和富集铅的生理特性,同时探讨铅污染土壤植物修复过程中土壤营养水平和添加EDTA浓度的不同对几种植物的修复效率的影响及应用前景,以期为深入研究铅污染土壤的植物修复技术的应用等提供科学依据和理论基础。现将本研究的主要结果归纳如下:1.通过试验比较了不同的无机营养水平下菠菜和苣荬菜对铅污染土壤修复及其对土壤中重金属铅形态改变的影响。结果表明:随着N、P、K浓度的增加两种植物地上和地下部分的铅浓度均增加,且最高的N、P、K浓度与对照相比能够使苣荬菜茎中铅浓度增加23.4%(P=0.0202),氮营养处理也分别能够增加菠菜和苣荬菜地下部根的铅浓度49.4%和57.7%(P=0.0106, P=0.0329),钾、磷营养对菠菜体内的铅浓度几乎没有什么影响。在两种植物比较中发现菠菜体内的铅浓度要低于苣荬菜,但由于菠菜的生物量远远大于苣荬菜,因此,菠菜对铅的植物提取能力反而大于苣荬菜。对土壤中铅形态的研究发现N、P、K营养液的添加能够使铅的非残留态向残留态转化。由此证明,氮和磷营养处理能有效的提高两种植物对铅的吸收,其中磷肥是低有机质铅污染土壤植物修复最有效的修复剂。2.通过试验比较了在铅污染土壤上三种植物菠菜、苣荬菜和马齿苋生物量、不同部分铅浓度和铅积聚的量。在三种植物中,菠菜和苣荬菜属于C3型植物种,而马齿苋属于C4型植物种。C4型植物种对热、干旱和盐环境的适应能力比C3型植物种强,同样C4型植物种的马齿苋对重金属Pb的胁迫环境的适应性也强于菠菜和苣荬菜。C4型植物种的马齿苋生物量在生长初期的8月25日达到了最大,而C3型植物种生物量在生长末期9月26日才达到最大。三种植物地上部和地下部的Pb浓度存在着差异,菠菜的地上部Pb浓度小于地下部,马齿苋的两者没有显著差异,而苣荬菜地上部的Pb浓度显著大于地下部,但是由于苣荬菜的生物量较小,因此整个苣荬菜体内富集的Pb总量是三种植物中最低的。体内Pb总量最大是菠菜,因此在中等Pb污染的土壤修复过程中应该选用菠菜。由于C4型植物种的马齿苋具有能够在生长早期就达到构件的成熟,并且有较高的重金属积聚量,因此在短期的修复工程,应该选用C4型植物种修复,这样可以在有限的时间内增加植物修复的次数。3.通过试验,比较了有机营养和EDTA对向日葵体内铅积累的影响及其EDTA添加次数对向日葵铅积累和产生的环境威胁进行了研究。结果表明:EDTA对铅的移动性存在着浓度依赖性,随着EDTA的浓度提高增加移动性(P<0.001)。有机营养处理对铅移动性的影响则存在着明显的不同,因为有机营养腐殖质对重金属铅存在移动和固定两种影响,因此中等有机营养对植物修复最为有效(P=0.002)。在低营养土壤中,相同浓度EDTA的单次添加相对于两次添加使植物地上部的铅浓度更低,因此EDTA的分次添加对植物修复更加有效,这是因为低浓度EDTA的分次添加对土壤的影响时效要长于同等浓度EDTA的单次添加(P<0.001)。通过试验也可以观察出向日葵是中等铅污染土壤植物修复非常有推广潜力的植物种。根据上述结果,不同营养水平和EDTA对铅污染土壤植物修复的机理及效率可以归纳为:N、P、K的添加能使土壤中的非残留态Pb向残留态转化,因此N、P、K的添加能够增加菠菜和苣荬菜体内的铅积累;与C3型植物菠菜、苣荬菜相比,C4型的植物马齿苋由于构件成熟期短,较为适合作短期内铅污染土壤修复工程;在植物修复过程中,低浓度EDTA的分次添加能够显著提高修复的效率,并且能够减小螯合剂增加产生的二次污染。本文的创新点在于:首次对植物修复过程中无机营养N、P、K元素和低剂量多频次添加EDTA的效果进行了比对研究,特别是研究了N、P、K元素对土壤中Pb形态的影响和土壤的肥力情况与分次添加EDTA的交互作用,初步解决了采用东北地区本地植物种进行植物修复的治理效率问题,避免采用非本地种可能引起的生态入侵等次生环境风险,对面源污染的植物修复的实施提供了科学依据和理论基础。低成本的N、P、K元素和低剂量多频次EDTA的添加也加强了植物修复过程中的成本控制,对在空间尺度较大的中等程度铅污染土壤上实施植物修复的广泛应用具有重要的意义。更多还原

【Abstract】 Soils contaminated with metals pose a major environmental and human health problem, which is still in need of an effective and affordable technological solution. The phytoremediation is a cost-effective“green”technology based on the use of metal-accumulating plants to remove toxic metals. In phytoremediation process, Pb mobility and the change of Pb fractionations were controlled by the physio-chemical properties of the soils, and Pb fractionations impacted on the toxic levels of heavy metal. The success of reclamation schemes is dependent greatly upon the choice of plant species and their methods of establishment. Mixed substrate of EDTA and NPK fertilizer has been used to restore contaminated soil in recent years, however, little is known about the effect of both major nutrient elements and EDTA on various forms and mobility of Pb and metal extraction. Plant growth and lead accumulation of accumulating and non-accumulating ecotypes of Sedum Spinacia oleracea, Sonchus arvensis, Portulaca olerace, and Helianthus annuus were studied with greenhouse pot experiments. To elucidate the characteristics of Pb tolerance and accumulation in the accumulating ecotype of plants, a series of chemical, biochemical analytic techniques were used to study the absorption, distribution of Pb at tissue and unit in plant, as well its application to phytoremediation. The major results were summarized as follows:1. In the greenhouse pot experiments, we studied influences of major nutrient elements on Pb phytoextraction of two crops (S. oleracea and S. arvensis) from a Pb-contaminated soil. Results indicated that the Pb concentrations in both shoots and roots of two crops ascended with increasing nutrient elements, and the highest nutrient treatment had the best effect as compared with other treatments in which the Pb concentrations in shoots of S. arvensis increased 23.4% (P=0.0202), and nitrogenous nutrient treatment had the best effect in which the Pb concentrations in roots of S. oleracea and S. arvensis increased 49.4% and 57.7% respectively (P=0.0106, P=0.0329), as compared with the control treatment. The potassic and phosphorus nutrient treatments had little effect on the Pb concentrations in plant tissues for S. oleracea. Pb concentration in S. oleracea was lower than S. arvensis. Because of the higher total biomass in S. oleracea than S. arvensis, the ability to Pb phytoextraction in S. oleracea was better than S. arvensis. Sequential extraction results indicated that the addition of soil amendments transform soil Pb from nonresidual fractions to residual fraction substantially. The results suggested that nitrogen and phosphorus amendments can effectively increase Pb uptake by two crops, and phosphorus fertilizer is the best amendment to remediate Pb-contaminated soil with low organic matter.2. We examined biomass accumulation, tissue concentrations of Pb, and net uptake of Pb in S. oleracea, S. arvensis, and P. olerace grown under greenhouse conditions in soil of middle Pb concentrations. Some physiological differences between S. oleracea, S. arvensis, and P. olerace include photosynthetic pathways (C3, C3, and C4, respectively). The transpiration rates and salt tolerance of C4 plants were greater than C3 plants. Whole plant biomass of P. olerace was significantly greatest on initial period August 25, but the greatest biomass of both S. oleracea and S. arvensis was on harvest period September 26. This difference in allocation was more profound at the middle Pb contaminated soil. In S. oleracea, significantly more of Pb concentration was allocated to belowground biomass (roots) than to aboveground biomass (leaves and stems), but S. arvensis was in reverse. No difference between aboveground and belowground of Pb concentration was in P. olerace. The highest pool of Pb was allocated to aboveground biomass in S. oleracea, so S. oleracea was a potential plant for remediation in middle Pb-contaminated soils. The grown period of tissues in P. olerace was short, so if the time of phytoremediation process was not abundant, the replacement of C4 plants with C3 plants may increase times and efficiency of remediation.3. Soil amendment application frequency contributes to phytoextraction of lead by sunflower at different nutrient levels. The main aims of this paper were to investigate whether a combination of nutrients and ethylenediaminetetraacetic acid (EDTA) enhanced Pb uptake of sunflower (Helianthus annuus) plants, and if timing of EDTA application altered Pb uptake and environmental persistence. Plants were grown in greenhouse pot experiments. Pb distributions and uptake of the whole plant were studied using chemical and flame atomic absorption spectrometry analyses. Pb mobilization by EDTA appeared to be dose dependent (P<0.001), with more mobilization for the high than the low dose. There were distinct differences in mobilization patterns of various nutrient amendments. EDTA mobilized Pb more in the medium than the highest and lowest nutrient levels. Heterogeneous soil humus components exerted mobilizing and stabilizing effects, so the medium nutrition was most effective for phytoextraction (P=0.002). At low nutrient levels, Pb concentration in the shoot with one low EDTA application was less than two applications to the same total EDTA dosage. So in the poor soil, two applications of EDTA was more effective than once. The half-life of two low EDTA treatment applications was longer than for one application, to the same total dosage (P<0.001). In general, sunflower was suited to phytoremediation of moderately Pb-contaminated soil by phytoextraction.The result mentioned above showed that the main reasons that nutrient and EDTA could impact on phytoremediation efficiency was these as below: firstly, the addition of soil amendments (N, P, and K) transform soil Pb from nonresidual fractions to residual fraction substantially. Secondly, the grown period of tissues in C4 plants was short, so the replacement of C4 plants with C3 plants may increase times and efficiency of remediation. Finally, two applications of low dose EDTA were more effective than once, and decreased secondary pollution. The innovative points of the study were that the phytoremediation efficiency with twice addition of low dose EDTA and nutrients (N, P, and K) were studied for the first time, the interaction of soil characters and EDTA addition and the affection of nutrients (N, P, and K) on soil Pb fractions were concerned emphatically, secondary environmental risk of ecological invasion was avoided, and scientific basis and theoretical foundation were supplied for non-point source phytoremediation. Addition of low cost nutrients and low dose EDTA in the process of phytoremediation was adopted in order to achieve goal to better control cost, hence which had important significance to wide application of phytoremediation on large area middling Pb polluted soil.更多还原