RCEES OpenIR  > 环境化学与生态毒理学国家重点实验室
土壤矿物对土壤可溶性有机质分子多样性的影响
Alternative TitleInfluences of soil minerals on molecular diversity of soil dissolved organic matter
黄灶泉
Subtype硕士
Thesis Advisor张淑贞 ; 吕继涛
2019-06
Degree Grantor中国科学院生态环境研究中心
Place of Conferral北京
Degree Name理学硕士
Degree Discipline环境科学
Keyword可溶性有机质,分子多样性,土壤矿物,分子分馏,傅立叶变换离子回 旋共振质谱 Dissolved Organic Matter, Molecular Diversity, Soil Mineral, Molecular Fractionation, Ft-icr Ms
Abstract

      土壤有机质是地表有机碳库的重要组成部分,而可溶性有机质(Dissolved organic matter, DOM)是其中最为活跃的组分,DOM 的动态变化对全球碳循环有着重要影响。此外,DOM 具有氧化还原、光学及生物活性,对污染物在环境中的迁移转化、生物可利用性及毒性均具有重要影响。由于DOM 构成的复杂性,我们对其化学组成和结构的认识仍然十分匮乏。近些年来,由于高分辨质谱的发展,特别是傅立叶变换离子回旋共振质谱(Fourier transform ion cyclotron resonance mass spectrometry, FT-ICR MS)技术的出现和不断升级,使得从单分子水平表征DOM 的分子组成成为可能。本论文以FT-ICR MS 技术作为主要研究手段,围绕土壤DOM 的提取方法、分子多样性及其在土壤矿物表面的分子分馏行为开展了如下研究:
       首先,对于土壤DOM 的分析需要选择合适的方法将其从土壤介质中提取出来,根据提取方法和试剂的不同,得到的土壤DOM 组成势必存在差异。在以往的研究中,除了常用的超纯水和NaOH,其它化学试剂如连二亚硫酸钠、盐酸羟胺和焦磷酸钠也被用于选择性地提取矿物结合的土壤DOM,但是,DOM 的分子组成是否会受到提取试剂的影响未见报道。本研究发现从总有机碳含量来看使用连二亚硫酸钠、盐酸羟胺和焦磷酸钠确实增加了土壤DOM 的提取效率,但是通过FT-ICR MS 对其分子组成的表征发现,这些试剂能够与DOM 反应直接改变DOM 的分子组成。DOM 与连二亚硫酸钠反应导致DOM 的含硫分子增加,而盐酸羟胺能与DOM 中的羰基反应,生成肟类化合物而大大增加含氮分子含量。相比而言,焦磷酸钠对DOM 分子组成的影响较小。因此,选择化学试剂提取土壤DOM 时需要特别注意试剂本身与DOM 分子之间的反应,以避免提取过程中生成人为的“假DOM”。由于水提取有机质(Water-extractable organic matter, WEOM)对土壤DOM 的外加影响小,更能够反映土壤可迁移DOM 的真实分子组成,因而被用于后续研究。
       为进一步揭示土壤DOM 的分子多样性,本研究选取采自全国各地的42 个土壤样品,利用FT-ICR MS 分析了土壤DOM 的分子组成。在所有土壤中共检测出10,039 个不同的DOM 分子,远高于报道的水体DOM,表现出高的分子多样性,其中仅含CHO 的分子占36.5%,含N 分子占34.9%,含S 分子占18.7%。
聚类分析发现土壤DOM 分子组成存在明显的地理分异,我国南方地区红壤DOM分子组成相似,均表现出芳香度低、不饱和度低、氧化度低等特征,显著不同于其它类型土壤DOM。多元统计分析发现土壤pH、铁碳比(Fe/C)和铝碳比(Al/C)是影响DOM 分子多样性的重要因素。随土壤pH 的升高,土壤DOM 中稠环芳香类化合物、多酚类化合物、高不饱和酚类化合物(O/C>0.5)的组分增加,高不饱和酚类化合物(O/C<0.5)和脂肪族化合物的组分减少。土壤Fe/C 和Al/C摩尔比对DOM 分子组成分布的影响与pH 呈现相反的规律,即Fe/C、Al/C 越大,DOM 的高不饱和酚类化合物(O/C<0.5)和脂肪族化合物的丰度越高,稠环芳香类、多酚类、高不饱和酚类化合物(O/C>0.5)的丰度越低。以上结果表明土壤铁铝氧化物选择性保留稠环芳香类和多酚类化合物是土壤有机碳储存的重要方式。
       土壤矿物对DOM 的选择性吸附引起DOM 在水-土界面的分子分馏,对土壤DOM 的分子多样性有着重要的影响,但目前对于DOM 在水-土界面分子分馏行为的主控因素仍不明确。本研究选取我国具有代表性的不同类型土壤及黏土矿物标准样品,研究了泥炭DOM(Peat leachate, PL)在不同土壤及土壤矿物表面的吸附和分子分馏行为。研究表明不同DOM 组分在水-红壤界面的吸附动力学存在明显差异:初始阶段PL 中所有组分均快速降低,稠环芳香类化合物初始吸附比例最高且持续增加,多酚类化合物初始吸附比例次之也随时间持续增加,而脂肪族化合物随时间增加其吸附比例降低,表明其逐渐被稠环芳香类和多酚类化合物代替。达到平衡时,PL 在水-土界面的分子分馏行为表现为分子量大、不饱和度高、芳香性强和极性强的DOM 组分容易进入矿物相,反之更容易保留在水相。
进一步通过研究PL 在一系列不同特征的土壤和矿物表面的分子分馏行为的结果表明铁氧化物含量与其分子分馏效应呈显著的正相关,而石英和黏土矿物对DOM 的吸附不具有选择性,对DOM 的分馏效应不明显。此外,发现PL 在红壤表面吸附上清液分子组成与红壤DOM 的相似,表明DOM 在水-土界面的分子分馏可能是红壤与其它土壤DOM 分子多样性存在明显差异的重要原因之一。

Other Abstract

      Soil organic matter is an important part of the surface organic carbon reservoir in terrestrial ecosystem with dissolved organic matter (DOM) as the most active fraction. Dynamic changes of DOM have a great impact on the global carbon cycle. In addition,DOM has redox, photochemical reactivity and biological activity, which influence the transport, transformation, bioavailability and toxicity of pollutants in the environment.
      Due to the complexity of the DOM composition, understanding of its chemical composition and structure is still very limited. In recent years, with the development of high-resolution mass spectrometry, especially the Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR MS), it is possible to characterize the DOM composition at molecule level. Three parts of studies were carried out in the present study, including extraction method of soil DOM, molecular diversity of soil DOM and molecular fractionation behaviors of DOM at soil mineral surfaces.
        Different reagents have been used to extract DOM from soils in previous studies,and ultrapure water and NaOH are the most widely used reagents. Besides, chemical reagents such as dithionite, hydroxylamine and pyrophosphate have also been used to selectively extract mineral-bound soil DOM. However, whether the extractions affect the molecular composition of DOM is still unclear. It was found in this study that dithionite, hydroxylamine and pyrophosphate did increase the extraction efficiency of soil DOM based on the total organic carbon. But we also observed that chemical reagents could react with DOM and then induced the changes in the molecular composition of DOM. The reaction of dithionite and DOM led to the increase of sulfur-containing molecules in DOM, while hydroxylamine reacted with the aldehydes in DOM to form oxime compounds, which greatly increased the nitrogen-containing molecules in DOM. Compared with strong reducing reagents, pyrophosphate had less effect on the composition of DOM molecules. Therefore, when selecting chemical reagents to extract soil DOM, particular attention should be paid to the reactions between the reagents and DOM molecules to avoid the generation of artificial "false DOM" during extraction. To avoid such influence, water-extractable organic matter (WEOM) was used in the following researches.
      To further reveal the molecular diversity of soil DOM, the molecular composition of 42 soil DOMs were analyzed by FT-ICR MS. A total of 10,039 unique molecules were detected in all the samples, much more than what has been reported for the aquatic DOM, of which CHO molecules accounted for 36.5%,nitrogen-containing molecules accounted for 34.9%, and sulfur-containing molecules accounted for 18.7%. Cluster analysis showed that there were obvious geographical differences in the composition of soil DOMs. The molecular composition of DOM in the red soils was characterized as low in aromaticity, saturation and oxidation, which was significantly different from other soil DOMs. Multivariate statistical analysis showed that soil pH, iron carbon ratio (Fe/C) and aluminum carbon ratio (Al/C) were the key factors affecting the molecular diversity of DOM. With increase of soil pH, condensed polycyclic aromatics, polyphenols, highly unsaturated and phenolic compounds (O/C>0.5) increased, while highly unsaturated and phenolic compounds (O/C<0.5) and aliphatic compounds decreased. With increase of Fe/C and Al/C ratios,the highly unsaturated and phenolic compounds (O/C<0.5) and aliphatic compounds increased, while condensed polycyclic aromatics, polyphenols, highly unsaturated and phenolic compounds (O/C>0.5) decreased. These results suggested that selective retention of polycyclic aromatics and polyphenols compounds by iron and aluminum oxides highly determined the organic carbon storage in soils.
       The selective adsorption of DOM by soil minerals causes molecular fractionation of DOM at the water-soil interfaces, which further affects molecular diversity of soilDOM; however, the main factors controlling the molecular fractionation behavior of DOM are still unclear. The adsorption and molecular fractionation behavior of peat leachate (PL) onto different soils and soil minerals were then studied. The results showed that there were obvious differences in adsorption kinetics among DOM components. At first, the red soil rapidly adsorbed all the DOM components with the highest proportion of polycyclic aromatics. Then, the adsorption of polycyclic aromatics and polyphenols increased while aliphatic compounds decreased with the increasing time, indicating that aliphatic compounds were gradually replaced by polycyclic aromatics and polyphenols. When reaching adsorption equilibrium, PL showed the pronounced adsorption fractionation onto the red soil. High molecular weight compounds, and compounds high in unsaturation and polarity had higher affinity to the red soil. Low molecular weight compounds, compounds low in unsaturation and polarity were preferentially maintained in solution. Further comparison of the molecular fractionation of DOM derived from adsorption on different soils and minerals indicated that molecular fractionation of DOM was mainly attributable to the high content of iron oxide in the soils and minerals, and the adsorption of DOM onto quartz and clay minerals was not selective. Furthermore, the composition of DOM molecules in supernatants after adsorption onto the red soil was similar to WEOM in red soils, which suggested that molecular fractionation of DOM at water-soil interfaces was probably one of the reasons why the molecular diversity of the red soil DOMs was significantly different from that of other soil DOMs.
 

Pages92
Document Type学位论文
Identifierhttp://ir.rcees.ac.cn/handle/311016/42280
Collection环境化学与生态毒理学国家重点实验室
Recommended Citation
GB/T 7714
黄灶泉. 土壤矿物对土壤可溶性有机质分子多样性的影响[D]. 北京. 中国科学院生态环境研究中心,2019.
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