【作者】 党亚爱；

【导师】 王国栋； 李世清；

【作者基本信息】 西北农林科技大学 ， 土壤学， 2008， 博士

【摘要】 碳和氮是土壤质量中最为重要的指标,它不仅反映土壤肥力水平,也印证着区域生态演变规律和生态建设的基本成果。黄土高原是我国主要生态脆弱区之一,多种不利因素制约着该区土壤有机碳氮积累,因此了解这一地区土壤碳氮空间分布特征及其相关关系,对进一步了解该地区土壤碳氮循环有重要理论意义。本文以黄土高原中部从北向南依次采集的干润砂质新成土(神木)、黄土正常新成土(延安)和土垫旱耕人为土(杨陵)等典型土壤剖面0-200cm土层土样,通过测定包括微生物量碳氮在内的土样有机碳氮主要组分含量,在明确各有机碳氮组分随地理位置和剖面分布规律的基础上,分析有机碳氮间的相关关系,以期为明确黄土高原南北主要类型土壤有机碳氮特征累积基本科学数据。通过研究,获得以下主要进展:1.明确了黄土高原南北主要类型土壤有机碳氮南北及剖面尺度空间分布规律。结果表明,不同土壤类型、不同土层土壤全氮和有机碳含量存在显著差异:同层次土壤从南到北全氮、有机碳含量显著下降,均以土垫旱耕人为土最高,黄土正常新成土次之,干润砂质新成土最低,差异显著(P<0.05);土壤有机碳、全氮含量在剖面上部(0-60cm)均存在一定厚度富集层,中部(60-120cm)二者含量有一定下降,下部(60-200cm)含量低而稳定;黄土高原南北主要类型耕层土壤有机碳、全氮含量低于全国耕层土壤有机碳、全氮含量平均水平;0-200cm土层土壤有机碳总储量沿土垫旱耕人为土(102.23t/hm~2)、黄土正常新成土(67.78t/hm~2)、干润砂质新成土(27.07t/hm~2)依次下降;三种土壤在100-200cm土层土壤有机碳累积量分别是0-100cm土层的65%、74%和58%;土壤氮储量也表现为土垫旱耕人为土(10.23t/hm~2)>黄土正常新成土(7.40t/hm~2)>干润砂质新成土(4.17t/hm~2),三种土壤在100-200cm土层土壤氮累积量分别是0-100cm土层的62%、59%和62%,因此在研究黄土高原南北主要类型土壤有机碳氮贮量时必需考虑深层贮量的贡献。2.通过对黄土高原南北主要类型矿物固定态铵的南北及其剖面分布规律的研究,认为矿物固定态铵是土壤氮库的重要组成部分。土壤矿物固定态铵从南到北呈下降趋势,但在全剖面上分布比较均匀,随土层深度变化差异不显著(P>0.05),且随土层深度增加,矿物固定态铵占全氮比例有先上升、后趋于稳定的变化趋势;矿物固定态铵的分布特点与土壤颗粒分布密切相关,土壤颗粒从南到北质地逐渐变粗,但在剖面分布相对均一,土壤体积分形维数结果进一步支持了这一观点:从南到北,同层次、同种土地利用方式下土壤体积分形维数呈下降趋势,而相同地理位置、不同土层土壤体积分形维数差异不显著。相关分析进一步表明,供试土壤中矿物固定态铵与<0.01mm物理性粘粒含量存在极显著正相关关系(r=0.5422),说明物理性粘粒是矿物固定态铵的主要载体,以上现象是黄土母质风成的必然结果,也进一步从矿物固定态铵的分布特征支持了黄土高原黄土母质的风成学说;干润砂质新成土、黄土正常新成土和土垫旱耕人为土矿物固定态铵在0-200cm土层累积量分别占土壤全氮累积量的61%、48%和41%,说明对矿物固定态铵占全氮地位的传统观念应予以重新评价。3.黄土高原南北主要类型土壤酸解有机氮及其组分随地理位置及剖面发生显著分异性。测定结果表明,从南到北,同层次、相同土地利用方式下土壤酸解性全氮、酸解氨态氮、酸解氨基糖态氮及酸解氨基酸态氮均呈下降趋势,酸解氨态氮、酸解氨基酸态氮及酸解未知态氮的相对含量较高,而酸解氨基糖态氮含量较低,其共性表现为0-40cm土层迅速下降,40-80cm土层随深度增加缓慢下降,80cm以下土层随深度增加基本保持在相同水平;供试土样除酸解氨基糖态氮外,草地土壤各有机氮组分在0-40cm土层内均高于同层次的农田土壤,但随土层深度增加,差异性减小;不同土类有机氮各组分在整个剖面上占酸解性全氮的平均比例不同:干润砂质新成土为酸解氨基酸态氮(38.2%)>酸解氨态氮(32.3%)>酸解未知态氮(24.9%)>酸解氨基糖态氮(2.5%);黄土正常新成土为酸解氨基酸态氮(36.0%)>酸解氨态氮(35.6%)>酸解未知态氮(23.1%)>酸解氨基糖态氮(3.1%);而土垫旱耕人为土为酸解氨态氮(53.3%)>酸解氨基酸态氮(29.0%)>酸解未知态氮(14.9%)>酸解氨基糖态氮(2.8%),以上结果说明酸解氨基酸态氮和酸解氨态氮是黄土高原南北主要类型土壤中最重要有机氮形态。4.在明确腐殖酸及其组分含量在土样中分布规律的基础上,发现黄土高原南北主要类型土壤从南到北胡敏酸/富里酸逐渐下降,但随土层深度增加而增加,说明黄土高原随土层深度增加,其腐殖酸稳定性增加。本研究土样腐殖酸所占土壤有机碳比例在全剖面变化幅度不大,整体上表现为占有机碳比例较小,土垫旱耕人为土在0-40cm、40-120cm和120-200cm土层土壤腐殖酸占有机碳比例分别为32.1%、29.9 %和26.6 %,黄土正常新成土分别为32.5 %、32.3%和33.4 %,干润砂质新成土在以上土层中腐殖酸占有机碳比例分别44.7%、46.0%和42.5%,说明在黄土高原较干燥条件下腐殖化过程缓慢,腐殖酸积累相对有限。土壤腐殖化度是衡量腐殖质品质优劣的标志之一,研究表明,随土层深度增加,土壤腐殖化度呈增加趋势,从南到北,同层次土壤腐殖化程度呈下降趋势;土垫旱耕人为土在0-40cm、40-120cm和120-200cm土层土壤胡敏酸/富里酸比值分别为0.56、0.55和0.65,黄土正常新成土胡敏酸/富里酸比值分别为0.35、0.49和0.64,干润砂质新成土在以上土层中胡敏酸/富里酸比值分别为0.20、0.55和0.60,从南到北,同层次土壤腐殖质品质呈下降趋势。5.通过对土壤各有机碳氮组分相互关系的分析,发现胡敏酸及重组有机质是黄土高原南北主要类型土壤酸解总氮和酸解氨态氮的重要贡献者,同时也揭示了胡敏酸及重组有机质在稳定黄土高原有机碳氮库方面发挥着重要作用,研究结果对理解黄土高原农田生产力形成具有重要参考价值。本论文通过对土壤有机碳氮组分间的相关性分析表明,全氮与微生物氮、固定态铵及有机氮各组分含量之间均达极显著相关性(p<0.01);有机氮组分间除了酸解氨基糖态氮与未知态氮之间没有显著相关性外,其余组分之间均达到显著(p<0.05)或极显著(p<0.01)相关;有机碳、微生物碳、胡敏酸、富里酸、轻组及重组含量相互之间的相关性均达到极显著水平(p<0.01),富里酸、轻组对微生物碳贡献率较高,分别是62.4%和70.7%,说明有机碳化学组分中的富里酸、物理组分中的轻组对微生物碳的影响最为显著;土壤全氮、酸解全氮、酸解氨态氮、氨基酸态氮和未知态氮含量均与有机碳物理、化学组分呈极显著相关性(p<0.01),酸解氨基糖态氮与上述有机碳组分均没有显著相关性,土壤固定态铵与土壤微生物碳和富里酸含量没有直接相关性。总体上看,胡敏酸及重组有机质是黄土高原南北主要类型土壤酸解总氮和酸解氨态氮的重要贡献者,同时也揭示了胡敏酸及重组有机质在稳定黄土高原有机碳氮库方面发挥着重要作用。更多还原

【Abstract】 Loess Plateau is one of the main ecologically fragile areas in China, and a variety of adverse factors constrain soil organic carbon and nitrogen accumulation of this area. Thus, knowledge of the spatial distribution of soil carbon and nitrogen in this region and their relationship has the important theory significance for a better understanding of soil carbon and nitrogen cycle in the region. The soil organic carbon and nitrogen , soil microbial biomass nitrogen and their relationship of three types of soils on the Loess Plateau collected from north to south (Ust-Sandiic Entisols at Shenmu , Los-Orthic-Entisol at Yan’an and Eum-Orthic Anthrosol at Yangling) were investigated to determine how they were affected by location and soil depth (0-200 cm) on the Loess Plateau. The main results of our research are shown as follows:1. Clarify the spatial distribution of soil organic carbon and nitrogen content of the main soil types on Loess Plateau. The results showed that the contents of total soil nitrogen and soil organic carbon differed significantly with soil types and soil depth. In the same depth, the contents of soil total nitrogen and soil organic carbon decreased significantly from south to north on the Loess Plateau, and the values were highest in Eum Orthic Anthrosols, intermediate in Los Orthic Entisols and lowest in Ust Sandic Entisols. The contents of soil total nitrogen and soil organic carbon in the profiles exsisted a certain thickness layer of soil organic carbon nitrogen enrichment within 0-60cm, decreased remarkably within 10-60cm, and remained low and stable within 60-200cm. Ortherwise, the contents of soil total nitrogen and soil organic carbon in the ploughing layer on the Loess Plateau were lower than the average values of the whole country. The total reserves of soil organic carbon peaked in Eum Orthic Anthrosols (102.23t/hm~2), followed by Los Orthic Entisols (67.78t/hm~2) and lowest in Ust Sandic Entisols (27.07 t/hm~2). The soil organic carbon storage in 100-200cm of the above three types of soil were 65%, 74% and 58% of carbon storage in 0-100cm respectively. The soil nitrogen storage decreased in the order Eum Orthic Anthrosols (10.23t/hm~2)> Los Orthic Entisols (7.40t/hm~2)> Ust Sandic Entisols (4.17t/hm~2), and the soil nitrogen storage in 100-200cm of the above three types of soil were 62%, 59% and 62% of carbon storage in 0-100cm respectively. Therefore, we should take into account of the reserves of lower 100cm soil as we evaluate the soil carbon and nitrogen storage on Loess Plateau. 2. The soil fixed ammonium was investigated to assess the influences of soil location and depth on its distribution on the Loess Plateau. The results indicated that fixed ammonium was the main component of soil nitrogen storage, and the traditional understanding of the status of fixed ammonium in total nitrogen should be reevaluated. The content of soil fixed ammonium decreased from south to north on the Loess Plateau, the distribution was well-proportioned among profile, and the content of soil fixed ammonium had no obvious change in the profiles (P>0.05). The percentage of fixed ammonium in total nitrogen increased with soil depth and then kept stable, resulting from the distribution of soil particle which was coarser from south to north. The result of the fractal dimension of soil aggregates the well-proportioned distribution among profile: the fractal dimension of soil aggregates in the same layer and similar land use decreased from south to north. However, the fractal dimension of soil aggregates in the same location and different soil layer had no significant difference. There was positive relationship between the contents of physical clays (<0.01 mm) and soil fixed ammonium (r=0.5422), indicating that physical clay was the primary carrier of soil fixed ammonium. This characteristic was an inevitable result of Loess Plateau formation and supported the eolian theory of loess parent material. The percentage of fixed ammonium in soil total nitrogen was 61% in Ust-Sandiic Entisols, 48% in Los-Orthic-Entisol and 41% in Eum-Orthic Anthrosol, indicating that the traditional understanding of the status of fixed ammonium in total nitrogen should be reevaluated.3. The contents of soil organic nitrogen and its components differed significantly with soil location and soil profile on the Loess Plateau. The results showed that the contents of total hydrolysable N、ammonia N、amino sugar-N and amino acid-N in the same layer and land use all declined from south to north. The relative content of ammonia N, amino acid-N and hydrolysable unknown N (HUN Fraction) were higher compare to that of amino sugar-N. All the four fractions in the profiles decreased remarkably within 0-40 cm, decreased slightly within 40-80 cm and remained at the lowest level below 80 cm. The contents of the components except for amino sugar-N within 0-40 cm in grassland were higher than that in field; however, the variability became slighter with the profiles. The percentage of the components in total hydrolysable N differed with soil type: amino acid-N(38.2%)>ammonia N(32.3%)>HUN Fraction(24.9%)>amino sugar-N(2.5%)in Ust-Sandiic Entisols;amino acid-N(36.0%)>ammonia N(35.6%)>HUN Fraction(23.1%)>amino sugar-N(3.1%)Los-Orthic-Entisol;and ammonia N(53.3%)>amino acid-N(29.0%)>HUN Fraction(14.9%)>amino sugar-N(2.8%)in Eum-Orthic Anthrosol. Indicating that amino acid-N and ammonia N were the major state of the soil organic N on the Loess Plateau.4. Explicate the content and distribution of the component of soil humus, we found that the ratio of soil humic acid and soil fulviic acid reduced from south to north on the Loess Plateau, but increased with the soil depth, indicating that soil humus became more stable with the soil layer. In this study, the percentages of soil humus in soil organic C were low and differed slightly with profile. The percentage was 32.1%, 29.9 % and 26.6 % within 0-40cm, 40-120cm and 120-200cm, respectively, for Eum-Orthic Anthrosol, 32.5 %, 32.3% and 33.4 % for Los-Orthic-Entisol, and 54.7%, 56.0% and 42.5% for Ust-Sandiic Entisols. These results indicated that the process of humification was low and the accumulation was limited, due to the dry climate on the Loess Plateau. The degree of humification was one of the indices evaluating the soil humus quality pros and cons. The results showed that degree of humification increased with soil layer, whereas decreased from south to north in the same soil layer. The ratio of soil humic acid and soil fulviic acid was 0.56, 0.55 and 0.65 within 0-40cm, 40-120cm and 120-200cm, respectively, for Eum-Orthic Anthrosol, 0.35, 0.49 and 0.64 for Los-Orthic-Entisol, and 0.20, 0.55 and 0.60 for Ust-Sandiic Entisols.5. Illustrate the distribution and relationship of soil microbial biomass carbon (MC) and light fraction organic carbon. The results showed that soil Mc and light fraction organic carbon revealed the similar rule of distribution with soil location and profile. Land use had significantly influence on the contents of the total soil N and soil organic carbon (SOC), and remarkable effect on the contents of soil MC and MN as well as light fraction organic carbon within 0-60cm. The contents of soil MC and MN, the ratio of MN and the total N, microbial entropy, and the content of light fraction organic carbon in grassland soil was slightly higher compared with farmland. The results indicated that the soil MC and MN, the ratio of soil MC and MN and soil organic nitrogen and carbon reflected the variation of soil quality more effectively. Soil light fraction organic carbon was significantly correlated with soil MC and MN. Soil light fraction organic carbon accounted 70.7% and 25.7% of soil microbial biomass carbon and nitrogen, whereas the percentage of heavy fraction organic carbon over soil microbial biomass carbon and nitrogen were 38.3% and 16.1%.The latter was lower than the former, indicating that the relationship for light fraction with microbes was closer, light fraction organic carbon was the main source of carbon and energy for soil microbes and microbial activity had remarkable influence on it. The results indicated that the variation of soil light fraction organic carbon reflected the variation of soil carbon storage more effectively.6. Through the analysis of the correlation among the soil organic carbon and nitrogen components we found that heavy fraction organic carbon and humic acid are important contributors for total hydrolysable N and ammonia N on the Loess Plateau typically region, but also reveals the humic acid and heavy fraction organic matter played an important role in the stability of the Loess Plateau of organic carbon and nitrogen. The results had important reference value in understanding the formation of the Loess Plateau farmland productivity. There was remarkable relationship between the contents of total N and soil fixed ammonium, as well as the soil organic nitrogen components (P<0.01). There was also remarkable or significant correlation between the content of soil organic nitrogen components excluding (P <0101). The contents of soil organic nitrogen components were highly correlated (p<0.01) or significantly correlated (p<0.05), but the correlation between amino sugar-N and HUN Fraction were not significant. The contents of soil organic N, MC, soil humic acid, soil fulviic acid l fraction organic carbon light and heavy fraction organic carbon were remarkably correlated (p<0.01). The percentage of soil fulviic acid and light fraction organic carbon over MC was 62.4% and 70.7%, respectively, indicating that the chemical composition of soil fulviic acid and the physical components of the light fraction organic carbon had most significantly impact on MC. The correlation analysis revealed that there were the significant correlations between soil total N, total hydrolysable N, ammonia N, amino acid-N and HUN fraction and the chemical and physical components of the SOC (P<0.01), except for amino sugar-N. And soil fixed ammonium had no direct relationship with the contents of MC and soil fulviic acid. In general, heavy fraction organic carbon and humic acid were important contributors to total hydrolysable N and ammonia N on the Loess Plateau typical region, but also revealed that the heavy fraction organic matter and humic acid played an important role in the stability of the organic carbon and nitrogen on the Loess Plateau.更多还原