Knowledge Resource Center for Ecological Environment in Arid Area
| 贵州喀斯特地区典型土壤和西北黄土剖面碳、氮同位素地球化学研究 | |
| 其他题名 | Isotope Geochemistry of Soil Carbon and Nitrogen in Typical Soil Types in Guizhou Karstic and Loess Plateau areas |
| 李龙波 | |
| 出版年 | 2012 |
| 学位类型 | 博士 |
| 导师 | 刘丛强 |
| 学位授予单位 | 中国科学院大学 |
| 中文摘要 | 以贵州为中心的西南喀斯特地区的石漠化和西北地区的荒漠化是我国实施西部大开发战略中所面临的两大根本性地域环境问题，喀斯特地区石漠化和黄土高原地区荒漠化是一种与脆弱生态背景和人类活动相关联的土地退化过程，而土壤退化是土地退化的核心部分。对喀斯特地区而言，土壤和植被是生态环境中最为敏感的自然环境要素，与非喀斯特地区相比，具有明显的脆弱特征，它们在人为活动干扰下植被覆盖度迅速下降、水土大量流失、侵蚀面逐渐接近基岩，从而导致石漠化的形成。而黄土高原地区是我国主要生态脆弱区之一，多种不利因素（干旱、水土流失、植被退化等）制约着该地区土壤有机质的积累。在土壤侵蚀与土地退化及全球碳循环的过程中，土壤有机质作为土壤重要组成部分和代表一个主要碳库在生态研究中起着关键作用，对土壤质量和气候变化都具有重大的影响，开展喀斯特和黄土高原地区植物及土壤有机质稳定同位素组成的研究是了解该地区生物地球化学循环的基础课题。\n 本研究选取中国西南喀斯特地区2种主要类型土壤（砂岩黄壤和石灰土）剖面和黄土高原地区不同植被覆盖下黄土母质剖面及其上覆植被为研究对象。分析了剖面样品的基本理化性质（pH值、有机碳、氮含量及C/N比值和土壤碳酸盐含量）和稳定同位素组成（δ13C、δ13CSIC和δ15N），揭示了喀斯特和黄土高原地区有机质的生物地球化学循环和无机碳循环的特点。为这些地区养分生物地球化学循环的研究提供了科学的论据，为喀斯特和黄土高原地区区域生态的改善及全球变化提供了理论依据。通过以上研究，获得如下主要结论：\n （1）砂岩黄壤和石灰土剖面土壤基本理化性质具有明显差异：砂岩黄壤的pH值一般小于4.5，石灰土的pH值一般大于5，且所有剖面的pH值从上到下逐渐增大；石灰土相应层次有机碳、氮含量较砂岩黄壤高。但黄色石灰土的有机碳、氮含量跟砂岩黄壤差异不大。砂岩黄壤和石灰土有机碳、氮含量均表现为从剖面上部向下逐渐降低的趋势，但它们随土层深度变化的速率却不同，前者较后者快，有机碳、氮主要集中在表层土壤；有机碳/氮比值在剖面上也呈现自上而下逐渐减小的特点；\n （2）砂岩黄壤和石灰土土壤碳酸盐（SIC）在剖面上的分布存在差异：石灰土相应层次SIC含量较砂岩黄壤高，在2.5~66.9 g·kg-1之间变化。但黄色石灰土SIC含量跟砂岩黄壤差异不大。黑色石灰土SIC含量在剖面上的总体变化均表现出从上到下逐渐减小的趋势，SIC主要集中在表层土壤，这可能与喀斯特山区石灰土的堆积成因有关。而黄色石灰土和砂岩黄壤SIC含量在剖面上的变化不大。2个黑色石灰土有机碳与碳酸盐之间呈明显的正相关关系，而砂岩黄壤和黄色石灰土剖面二者之间的关系不明显。\n （3）黄土地区土壤pH值在7.1~8.9之间，呈弱碱性-碱性，有利于次生碳酸盐的形成。各剖面pH与植被类型密切相关，植被类型可能通过控制有机质分解和土壤呼吸等方式，在一定程度上影响土壤酸碱度。其变化趋势为：荒地>草地>林地；不同林地的pH也有变化：阔叶林>灌木林>针叶林；有机碳含量变化范围为1.1~31.2 g·kg-1，且随土层深度增加而逐渐降低。SOC主要集中在表层土壤，其含量变化规律为阔叶林地＞针叶林地＞灌木林地＞草地＞荒地。但各剖面SOC在不同土壤层次处出现急剧下降。其中，阔叶林地和针叶林地在10 cm深度处，灌木林地和草地在20 cm深度处和荒地在5 cm深度处，SOC含量急剧下降。但60cm深度以下各剖面SOC含量变化均较小，这主要是因为土壤成土母质大致相同造成的，此时植被类型的差异对其影响不大；在剖面垂直分布上，有机氮主要集中在表层土壤（0~20cm）且均随凋落物层向下逐渐减少，呈倒“L” 形分布。与有机碳含量的剖面深度变化相比，有机氮20~60cm深度内呈现出锯齿型变化且变幅不大；60cm深度以下，土壤有机氮趋于稳定；土壤C/N比值除灌木林地呈现先增加后减小的趋势外，其它4个剖面都是随着土层深度的增加而降低。但灌木林地和阔叶林地土壤的C/N比值在60cm以下变化比较复杂，呈现锯齿型下降。这也是不同植被覆盖对土壤有机碳和有机氮影响的综合结果。土壤C/N比值大小显示荒地有机质分解程度较低；\n （4）黄土剖面SIC在5.7~14.1%之间，其中针叶林表层SIC含量最低，阔叶林次之。除个别层位外，灌木林，草地和荒地SIC含量在土壤剖面无明显变化。各个剖面SIC均值大小：荒地>草地>林地；林地中，阔叶林>灌木林>针叶林。其主要原因归纳起来有2个方面：1）植被类型通过对SOC的输入间接影响土壤呼吸和SIC的迁移转换过程。2）黄土质地均匀，含有丰富的原生碳酸盐。成土过程中原生碳酸盐通过溶解-迁移-沉淀在淀积层形成次生碳酸盐，造成SIC含量增高。SOC与SIC存在负相关关系；研究区pH与SIC之间具有一定的正相关关系。由于土壤pH变化范围比较小，土壤pH值与SIC含量相关关系并不显著。因此，黄土地区的次生碳酸盐并不是控制土壤pH的主要因素。\n （5）喀斯特地区研究剖面在枯枝落叶转化为表层土壤有机质的过程中，砂岩黄壤和石灰土δ13Csoc值分别升高了2.6‰~3.0‰和5.5‰~6.3‰。石灰土δ13Csoc值变幅高于砂岩黄壤。与砂岩黄壤相比，石灰土δ13Csoc值随土壤深度的加深呈现出上升-降低-不变的变化趋势，这可能与喀斯特山地石灰土形成过程，即经历了堆积风化成土过程有关。而砂岩黄壤δ13Csoc值从表层到底部有偏正趋势，这表明砂岩黄壤中有机质随土壤深度的增加分解更彻底。但2种类型土壤δ13Csoc值随土壤深度的变化幅度各不相同，反映了土壤有机质分解过程中碳同位素分馏效应的强弱程度，分馏程度大小依次为黄色石灰土>砂岩黄壤>黑色石灰土。成土过程及程度上的差异和不同土层成土环境可能是导致2种类型土壤有机质剖面分布和稳定碳同位素组成差异的主要原因。另外，土壤有机质分解过程中的碳同位素分馏效应可能受到土壤类型、土壤pH值等综合因素的影响；\n （6）砂岩黄壤和石灰土剖面上枯枝落叶的 δ15N 值低于植物叶片和表层土壤的δ15N 值。其中砂岩黄壤和石灰土表层土壤有机质的δ15N 值变化范围分别为2.9‰~3.1‰，3.9‰~4.8‰。在枯枝落叶转化为表层土壤有机质的过程中，砂岩黄壤和石灰土δ15N值分别升高了5.1‰~5.4‰和6.5‰~8.1‰。石灰土δ15N值变幅高于砂岩黄壤。从剖面表土向下，砂岩黄壤δ15N值均出现逐步增加的趋势，而石灰土δ15N值的变化却比较复杂，这可能归因于土地利用的改变和土壤堆积。与砂岩黄壤相比，石灰土δ15N 值的变幅较小的主要是由于其具有较高的土壤pH，粘土矿物和更多的钙镁元素富集在石灰土中。\n （7）喀斯特地区2种主要的土壤类型石灰土和砂岩黄壤碳酸盐碳同位素(δ13CSIC值)组成存在差异：2个黑色石灰土δ13CSIC值随土壤深度变化具有相似的变化特征，总体上都呈现出锯齿型下降至一定深度后趋于稳定的趋势。而砂岩黄壤δ13CSIC值从表层到底部有偏正的趋势。但2种类型土壤δ13CSIC值随土壤深度的变化幅度各不相同，反映了土壤有机碳向无机碳的转化程度。成土过程及程度上的差异和不同土层成土环境（如生物、气候等）可能是导致两种类型δ13CSIC值组成差异的主要原因；\n （8）黄土地区各剖面在枯枝落叶转化为表层土壤有机质的过程中，δ13Csoc值升高了0.5‰~3.2‰，与其它地区相比13C富集更大。剖面δ13Csoc值在-26.3‰~ -20.8‰之间变化，均随着土壤深度的加深而增加。但不同植被条件下的变化幅度各不相同，这反映了土壤有机质分解过程中碳同位素分馏效应的强弱程度。剖面有机质碳同位素分馏程度的变化规律为阔叶林地>针叶林地>草地>灌木林地>荒地。这可能是由于阔叶林地上生物量大及微生物对有机质的分解作用强，有机质来源较多且组成、结构不同所致。而荒地剖面坡度很大，地上植被来源较单一，表层枯枝落叶很少，故导致其剖面土壤有机质的分馏效应最低；\n （9）黄土剖面在枯枝落叶转化为表层土壤有机质的过程中，δ15N值升高了0.7‰~4.5‰。该过程中15N值富集的一个主要原因是表层新鲜枯枝落叶的输入和有机质分解过程中的同位素分馏。另外，δ15N 值的变化主要受表层土壤有机质的周转率控制，但不同植被类型覆盖下黄土剖面δ15N值变化幅度各不相同，反映了土壤有机质分解过程中氮同位素分馏效应的强弱程度。分馏程度大小依次为阔叶林地>针叶林地>草地>荒地>灌木林地。有机质分解过程中尽管碳释放较氮快和C/N比值随土壤深度的加深而逐渐减小，但δ15N 值随土壤深度的变幅高于δ13C 值。这主要是由于有机质分解过程中15N富集较13C更大，这可以更好的解释在有机质腐殖化过程中研究区剖面土壤有机氮同位素分馏较碳同位素分馏大；\n （10）黄土各剖面δ13CSIC值在-6.2‰~-1.8‰范围内变化。表层40cm内，δ13CSIC值：荒地>草地、灌木林、针叶林>阔叶林；40~60cm内，阔叶林δ13CSIC值呈波动状升高；60cm以下，灌木林δ13CSIC值稍微升高后在100cm以下又与其他林地保持一致；针叶林、草地和荒地剖面中δ13CSIC值变化不明显。其主要原因归纳起来有3个方面：1）荒地成土过程缓慢，原生碳酸盐多残存在土壤中。导致荒地δ13CSIC值最高；2）不同类型植被覆盖下形成的次生碳酸盐具有不同的δ13C值；在植被正向演替序列中，土壤次生碳酸盐δ13C值具有偏负的趋势；3）针叶林δ13C值在剖面变化不明显可能是由于针叶林是人工次生林，其演化成林时间相对较短造成的。\n \n关键词：土壤有机质；碳同位素；氮同位素；喀斯特地区；黄土地区；中国 |
| 英文摘要 | Rock desertification of Karst Mountains widely occure in Guizhou Province, southwest China and desertization in northwest China, which are the two fundamental regional environmental issues in the process of carrying out the strategy for great development of west China. It is now recognized that rock desertification in karst and desertification in loess plateau areas are the processes of land degradation, which are most likely resulted from the comprehensive irrational actions on the fragile eco-geo-environment. Soil degradation is the core of land degradation. Compared with the non-karst areas, soil and vegetation in the karst areas are the impressionable natural environmental elements and have an obviously characteristic. Under the interference of anthropological activities, they have experienced a quick decline of vegetation coverage, severe water and soil loss and erosion near to bed rock, as a result of the rock desertification. Whereas the Loess Plateau region is one of the fragile regions in China and there are many factors limiting the accumulation of soil organic carbon (SOC), such as aridity, erosion and vegetation degradation, and so on. In the process of soil degradation and global carbon cycle, as an important composition of soil and a major carbon pool of the terrestrial carbon reserves, soil organic matter (SOM) plays a key role in an ecosystem. The study of the stable isotope composition of vegetation and soil organic matter in karst and loess plateau areas, therefore, is basic to understand the biogeochemistry cycle in this region.\n This study selects the typical karst areas in Guizhou province and loess plateau in Northwest China as study sites. The stable carbon and nitrogen isotope composition of dominant plant leaves, litter, SOM in bulk soil of soil profiles, and the SOC contents, soil organic nitrogen (SON) contents, pH values and soil carbonate contents (SIC) are measured. The main objectives of this study are to reveal the characteristics of the inorganic carbon cycle and the biogeochemical cycling of SOM in karst and loess plateau, and to provide a useful argument for biogeochemical cycling of nutrients in those areas, and finally to obtain a theoretical basis for regional ecological improvement and understanding of global change in karst and loess plateau. The main conclusions have been reached as follows:\n(1) Basic physicochemical properties of yellow sandstone soil and limestone soil profiles are distinct. The pH values of most samples from the yellow sandstone soil profiles are less than 4.5, while the limestone soil profiles larger than 5 in general. All the profiles show a gradual increase in pH with the depth. The amounts of SOC and SON mainly concentrated in the surface soil and decrease with increasing depths, and show different amounts in different type of soils, with the SOM in limestone soil significantly higher than those in the yellow sandstone soil. A decreasing tendency from the surface to the bottom of both the yellow and limestone soil profiles was observed, so does the C/N ratio.\n(2) SIC contents of yellow sandstone soil and limestone soil profiles are distinct. Limestone soil had a higher content of SIC, as compared with yellow sandstone soil. The SIC content in the profile of limestone soil varied in the range of 2.5~66.9 g·kg-1. The SIC content in black limestone soil decreased with increasing soil depth, the amounts of SIC mainly concentrated in the surface soil, which can be mainly ascribed to soil accumulation in limestone soil. The significantly positive correlated is found between the two limestone soil profiles, while there have not the positive relationship between the yellow sandstone and yellow limestone.\n(3) All soils were alkaline (pH-CaCl2) ranging from 7.1 to 7.9 (mean=7.5) in the Loess plateau profiles. The variation of pH values with depth was similar within all profiles at sampling sites. According to the changes of vegetation condition, the pH values differentiated in the following order: wasteland> grassland > broad-leaved forest > shrub forest > coniferous woodland. The SOC was mainly enriched in the surface soils and decreased with increasing depths. SOC contents varied in the range of 1.1~31.2 g·kg-1. It was found that, the SOC content of the soils differentiated according to the vegetation condition, in the following order: broadleaves plant > coniferous plant > shrub > grassland >wasteland. The rapidly changes of layers are the 10 cm for the broad-leaved forest and coniferous forest, 20 cm for the shrubs and grassland and 5 cm for the wasteland. The SOC contents decrease slowly below the 60 cm in studied soil profiles, which can be mainly ascribed to the same soil parent material. The amounts of SON mainly concentrated in the surface soil (0~20cm) and decrease with increasing depths, and show different amounts in soil profiles under different vegetation conditions. The SON shows distinct change at 20~60 cm depth and below the 60 cm depth, the SON almost constant to the bottom, as compared with SOC content. Mass ratios of C/N in shrub forest increased slightly and then decreased with soil depth, while the ratios for the surface soil of the other profiles decreased continuously with depth. But the variations of C/N mass ratios were very confusing below 60 cm depths in broad-leaved forest and shrub forest, which can be mainly ascribed to the different vegetation conditions. The C/N mass ratios show the wasteland had the less decomposition of organic matter.\n(4) The SIC contents varied in the range of 5.7% ~14.1%. It was found that the SIC contents of the soils varied according to the vegetation, in the following order: wasteland >grassland > forest land; and Broad-leaved forest>Shrub>Coniferous forest. The major reasons are follows: 1) The transformation of SIC is controlled by the input of SOC from different vegetation types indirectly; 2) The loess is homogeneous and rich of primary carbonate which can transfer to secondary through dissolution-migration-deposition. It is due to the high content of SIC in some sections. The significant negative correlations exist between the contents of SOC and SIC, the positive correlations exist between the pH and SIC in the soils. The variation range of the soil pH is not large, the correlations between the pH and SIC are not significant in the soils, which indicate pedogenic carbonate is not the main factors controlling the pH in the soils. \n(5) The δ13Csoc in limestone soil profiles had wider variation range than that in yellow soil profiles during litter degraded into SOC in surface soil. The δ13Csoc increased by 2.6‰~3.0‰ in yellow soil profiles and by 5.5‰~6.3‰ in limestone soil profiles. Compared with the yellow sandstone, in limestone soil profiles the δ13Csoc were generally high in the surface layers, then increased rapidly down to a depth of about 20 cm, and finally decreased slowly, which can be mainly ascribed to land use change and soil accumulation. While the δ13C values of SOM increase with depth in yellow sandstone soil profiles, which indicate that the degradation of SOM became intense with increasing soil depth. The 13C-fractionation in different soil profiles was decreased in the following order: yellow limestone soil>yellow sandstone soil>black limestone soil. The difference in 13C- fractionation was ascribed to the vegetation conditions and difference soil-forming environments (such as climate, biology, etc.) in different soil layers. Moreover, the 13C-fractionation during the decomposition of SOM mainly due to the soil types and soil pH values in soil profiles. \n(6) Unlike the δ13C value, the δ15N average values of plant litter are lower than those of the plant leaf and SOM of top soil for both types of the soil profiles. The SOM in top soils of yellow sandstone and limestone soil profiles varied in the range of 2.9‰~3.1‰, 3.9‰~4.8‰, respectively. The δ15CSON in limestone soil profiles had wider variation range than that in yellow sandstone soil profiles during litter degraded into SOC in surface soil. The δ15CSON increased by 5.1‰~5.4‰ in yellow soil profiles and by 6.5‰~8.1‰ in limestone soil profiles. The δ15N values of SOM increase with depth in yellow sandstone soil profiles, which indicate that the degradation of SOM became intense with increasing soil depth. The relationship that increase of the δ15N values with decreasing SOM content, in the yellow sandstone soil strongly argue for the SOM decay and hence induced increment of δ15N values in deeper soil horizons of the yellow sandstone soil profiles. But the δ15N values of SOM in limestone soil profiles have a complex variation trend with increase of soil depth and SOM contents, which can be mainly ascribed to land use change and soil accumulation. Compared with the yellow sandstone soil profiles, the limestone soil profiles have smaller variation in δ15N values, mainly due to the soil pH value, clay contents and more calcium and magnesium elements abundant in limestone soil profiles. \n(7) The depth distribution of δ13CSIC in yellow sandstone soil is quite different from that in limestone soil. The δ13CSIC increase with depth in yellow sandstone soil profiles, but the δ13CSIC in limestone soil profiles have a complex variation trend with increase of soil depth, which can reflect the degree of transformation of SOC to SIC. The difference in 13C-fractionation was ascribed to the vegetation conditions and difference soil-forming environments (such as climate, biology, etc.) in different soil layers.\n(8) Compared with the other regions, the 13C was enriched and the δ13Csoc increased by 0.5%~3.2% during litter degrading to SOC in surface soil. The δ13C composition of SOM increase with depth, the δ13C values of SOM are between -26.3‰ to -20.8‰ showing a significant difference exists in vertical patterns of variation, but the variation range were different in different soil profiles. In general, the variation of δ13C in different soil profiles was decreased in the following order: broadleaves plant > coniferous plant >grassland > shrub >wasteland. This may be resulted from the abundant litter materials (e.g., leaf fall) in broadleaved forest and more active microbial action in its soil and forms a higher carbon isotope fractionation of organic matter. The wasteland has seldom vegetation cover and litter was in a small amount in the topsoil and a less fractionation of SOC.\n(9) The 15C was enriched and the δ15NSON increased by 0.7%~4.5‰ during litter degrading to SOM in surface soil. There were two controls of soil nitrogen isotopic compositions: new litter inputs and overall isotopic fractionation during decomposition. Moreover, the δ15NSON increased with soil depth mainly due to the turnover rate of SOM, but the variation ranges were different in different soil profiles. In general, the variation of δ15NSON in different soil profiles was decreased in the following order: broadleaves plant > coniferous plant >grassland > wasteland > shrub. It is concluded that although C is released more rapidly than N during organic matter decay and although C/N mass ratios decrease with soil depth, δ15N values increase more than δ13C values. This is because overall discrimination against heavy isotopes during decomposition is greater for 15N than for 13C. It is to better decipher the N isotopic fractionation within our soils profiles studied is higher than that of the C isotope.\n(10) The value of δ13CSIC is between -6.2‰ and -1.8‰. From 0 to 40cm depth, the variation of δ13CSIC in different soil profiles decreased in the following order: wasteland> grassland、shrub、coniferous forest>broad-leaved forest; From 40cm to 60cm depth, the δ13CSIC of broad-leaved forest is fluctuating rising; Under the 60cm depth，the δ13CSIC of shrub rise a little and back to the average of other forest; There is no obvious changing in coniferous forest、wasteland and grassland. There are a few causes due to this phenomenon. such as: 1) Desert land has a slowly soil-forming process and has the remaining primary carbonate which δ13C value is high; 2) The δ13C of secondary carbonate vary with vegetation types; In the positive sequence of vegetation evolvement, the δ13C of secondary carbonate has a negative tendency; 3) the δ13C coniferous forest is secondary forest and has a short forest forming time, which may explain its insignificant change. \n \nKey words: Soil organic matter, carbon isotope, nitrogen isotope, karst, loess plateau, china |
| 中文关键词 | 土壤有机质 ; 碳同位素 ; 氮同位素 ; 喀斯特地区 ; 黄土地区 ; 中国 |
| 英文关键词 | Soil organic matter carbon isotope nitrogen isotope karst loess plateau china |
| 语种 | 中文 |
| 国家 | 中国 |
| 来源学科分类 | 地球化学 |
| 来源机构 | 中国科学院地球化学研究所 |
| 资源类型 | 学位论文 |
| 条目标识符 | http://119.78.100.177/qdio/handle/2XILL650/287059 |
| 推荐引用方式 GB/T 7714 | 李龙波. 贵州喀斯特地区典型土壤和西北黄土剖面碳、氮同位素地球化学研究[D]. 中国科学院大学,2012. |
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