【作者】 刘彬；

【导师】 罗承德；

【作者基本信息】 四川农业大学 ， 森林培育， 2013， 博士

【摘要】 中国西部亚高山针叶林是低纬度高海拔地区亚高山森林植被的重要组成部分,具有涵养水源、保育物种等重要生态功能,多样化的植被、土壤组合也为森林土壤学研究提供了天然的实验室。川西亚高山冷杉林因所处生境自然气候条件(相当于寒温带气候)和暗针叶林建群种特性形成了低温、高湿、季节性冻融等有别于同纬度地带针叶林的林下环境。其林下土壤的形成和发育也具有下自身的特殊性。曾经一度,土壤学家为低纬度高海拔、高纬度低海拔地区亚高山针叶林下土壤类型的归属争论不休。随着研究手段、研究焦点的不断提高和转变,诸如成土过程与特征等基础研究逐渐被忽略,这不利于森林土壤学的长期发展,更不能有效指导森林的经营与管理。因此,本文以川西亚高山冷杉林下土壤为研究对象,采用森林土壤定位研究法,重点研究了土壤诊断特征、土壤水热动态,土壤溶液及固相土壤元素移动、土壤氧化还原体系等土壤形成过程与发育特征。研究结果表明,(1)定为研究点的土壤按美国土壤系统制应归入始成土纲(Soil Survey Staff,1996),按中国土壤分类系统,以归入淋溶土纲漂灰土类为宜。定位研究点土壤属于A-E-B-C型发育土壤,有明显的有机层、淋溶层、淀积层和母质层。诊断表层淋溶层(A2)颜色为湿态下灰(Gleyl5/N)、干态下浅灰(2.5Y7/1)已经达漂白物质的颜色标准(彩度<2,a湿态亮度>3与干态亮度>6,或b湿态亮度>4与干态亮度>5),这说明层次可判定为漂白层。相比较,淀积层(B2)土壤颜色分别为湿态下红(10R4/8)、干态下黄(-深)棕色10YR5/6(-7.5YR5/6)。土壤质量含水量、田间持水量、最大吸湿水、孔隙度均随土壤深度加深而减小,而土壤容重、石砾含量等随着土壤深度加深而增大。土壤通气度和土壤烧失量有其特殊的变化规律,即在漂白层土壤通气度和烧失量显著低于其它土层。土壤中矿物以原生矿物石英、长石族矿物为主,没有检测到粘土矿物的存在。土体中发生的主要化学过程是从表层A1开始的,有机质含量、腐殖质含量、矿质元素含量大多数以该层次最高。在剖面层次上,腐殖质多以酸性、活性强的富里酸为主。土壤剖面物质的淋移和淀积分析结果表明,硅在表层含量较低,但在漂白层表现出富集趋势。定位研究点虽有腐殖质络合淋溶形成的灰化淀积层,但色调、明度、彩度以及活性铁铝含量均不满足真正灰壤的灰化淀积层标准。(2)定位研究点的土壤温度、水分、能量表现出显著的干湿季节变化。在旱季(11月和2月)时,11月时漂白层和淀积层土壤含水量很接近,而在2月表现出B2层土壤质量含水量显著低于A2层。而随着雨季到来以及上层漂白层先于淀积层逐渐解冻,A2层冻结的土壤固态水融化下移至B2层冻结,表现为B2层土壤质量含水量平稳显著升高,A2层土壤含水量降低并出现波动。但就总量而言,A2层土壤中的水分含量在各个季节均高于B2层土,两个层次的土壤水分含量最高值均出现在雨季(8月),最小值分别出现在旱季11月和2月。与水分耦合的温度在未降至土壤水冻结冰点时表现出先下降后上升再下降的昼夜变化规律,淀积层土壤温度昼夜变化幅度较小。一年之中,土壤温度变化经历两个阶段,一是淀积层高于漂白层(B2>A2,9月22号-笠年4月6号),持续约7个月,第二个阶段则是漂白层高于淀积层(B2<A2),这个阶段持续约5个月。由土壤温度主导的土壤水能量梯度导致了土壤水的移动,即在6月至9月,土壤水由淋溶层向淀积层移动；10月后,土壤水具有往上移动的趋势。A2和B2层土壤中含有一定盐份,冻结的冰点均小于零度。因此,即便土壤温度降至零度,土壤仍未进入冻结状态,此时土壤中液态水处于形成晶核的阶段。只有当土壤温度温度降至冰点以下,并持续低于冰点过冷,土壤才会结冻。A2、B2共同处于冻结期的时间为50D(4.16-6.7)(包括结冻和融化过程),共同处于正常状态的为191D(6.13-12.24),其余则为A2或B2处于冻结期或正常态。定位研究区全年约180D处于融通正常状态,仅有50D处于土体冻透状态。(3)铁、铝、锰等成土标型元素在漂灰土最大淋溶层(漂白层)和最大淀积层间的存在形态和含量具有显著的干湿季节变化规律。在雨季(8月和5月),可溶态铁中的亚铁离子含量显著高于三价铁离子,而在旱季(11月和2月)三价铁离子含量则显著升高,在可溶态铁中所占比重增大。但季节性的雨季和旱季变化未影响土体中漂白层和淀积层可溶态铁和碳酸盐结合态铁含量分配,即漂白层可溶态铁和碳酸盐结合态铁含量显著低于下层淀积层含量,这在雨季表现得更为强烈；腐殖质态和铁锰结合态未随季节变化而变化,而且含量仍以淀积层较高。成土标型元素的分布与移动,表明土体中进行着两种主要的化学过程,一是铁、锰还原性淋溶即漂洗过程；二是铁、铝与酸性腐殖质(以富里酸为主)及其他多酚类有机物进行螯合淋溶。尽管定位研究点的土壤中漂白层中也有游离铝的存在,但游离铁更容易与酸性腐殖质螯合淋溶,在淀积层被氧化固定。游离铝则更多的参与土壤中发生的交换作用。因此,土体中发生的螯合淋溶则主要是铁在主导。(4)定位研究点漂灰土氧化还原体系中起主要作用的是有机还原性物质中的甲酸等低分子有机酸,以及具有变价态的铁。漂灰土的形成过程中,低分子有机酸和铁的价态变化、移动是主要的氧化还原反应体系和过程,并强烈的影响着漂灰土漂白层和淀积层形态和化学特征的形成。川西亚高山冷杉林凋落物以凋落物叶为主(占总凋落物的89.45%)。凋落叶的主要归还期集中在9-11月,分别在全年凋落叶总量和凋落物总量的60.32%、48.52%。凋落物提取液中含有多种低分子有机酸,以甲酸等单羧酸低分子有机酸含量较高,并主导着土壤溶液中低分子有机酸含量的种类和数量。同一季节中A2层土壤氧化还原电位均低于B2层土壤。在比较不同pH值下的Eh时,建议将Eh和pH值并列表示的方法较为适宜。铁在不同土层的分布状况与土壤氧化还原电位的变化密切相关。A2层土壤在旱季和雨季大多处于还原状态,矿质元素铁呈现高价态的较少,绝大多数呈低价还原状态,溶解度较高,并以不同形态向下层土壤移动；当不同形态的低价铁下移到B2层土壤,B2层土壤虽与大气接触的机会比A2层土壤少,但氧化还原电位较A2层高,土壤基本上处于氧化状态,这时呈还原状态的低价铁被氧化成固态的氧化物或氢氧化物(如Fe203或Fe(OH)3)淀积于B2层土壤中,形成一个铁、铝、锰共同淀积的红色或棕色淀积层。同时,在土体上部矿物中的铝硅酸盐经有机质产生的有机酸在厌氧条件下被还原蚀变分解后留下Si02,形成一个Si02相对富集的灰白色淋溶层,即漂白层。值得注意的是,漂白层的颜色除Si02相对富集外,A2层土壤因大多处于还原状态,一部分高价铁被还原成低价铁即Fe2+化合物,Fe2+通常情况下呈现浅绿色,所以从定位研究点挖掘出的土壤剖面中发现A2层土壤的颜色除了灰白色,还夹杂着少量的青灰色。(5)最大淋溶层(A2)、最大淀积层(B2)层土壤的铵态氮、速效钾含量在雨季(8月和5月)含量显著高于旱季(11月和2月)的含量,而硝态氮则反之。雨季时,铵态氮、有效磷、速效钾表现为A2层含量显著高于B2层含量,而在旱季时,B2层含量与A2层含量较为接近,或显著高于A2层。土壤有机碳含量在各个季节含量均表现为淋溶层大于淀积层。土壤全氮、全磷含量则表现为B2层高于A2层。钾、钠等矿质全量随土壤水分的季节性变化而发生季节性的变化,雨季时,淋溶层高于淀积层,旱季时,淀积层反而高于淋溶层。钙、镁、铜、锌、镍等矿质全量在淋溶和淀积层的变化不显著。由此可见,漂灰土并没有导致土壤淋溶层严重贫瘠化。更多还原

【Abstract】 Subalpine fir forest (Abies faxoniana) in western China plays important part in subalpine forest located in high elevation and low latitude area. What’s more, subalpine fir forests have principle ecological functions such as water conservation, species conservation and other important ecological functions. Its diverse vegetation and soil association provide a natural laboratory for forest soil science studies. The understory environment of subalpine fir forests, which is low temperature, high humidity, seasonal freezing and thawing, is very different from coniferous forest in the the same latitudes due to its natural climatic conditions (equivalent to cold temperate climate) and the properties of construction species of dark coniferous forest. Therefore, the soil formation and development has its particularity under subalpine fir forest. For a time, soil scientist debated the soil type under coniferous forest at low latitude and high altitude, or at high latitude and low altitude. With the improvement of research methods and the change of research focus, soil basic research, such as soil forming process and the basic characteristics, has been neglected. This phenomenon is not conducive to the rapid development of forest soil science, nor effective in guiding forest management. Thus, in this case, it takes subalpine fir forest soil as the research object using located research methods. And, it has the important theory and the practice significance that focus on the diagnostic soil characteristics, soil water and heat dynamics, the mobile of soil elements in soil solution and solid phase, soil redox system process and other soil formation and development characteristics. The results indicate that,(1) The soil in located research position is A-E-B-C soils the means this soil has obvious organic layer, leached layer, deposition layer and the matrix layer. Notably, the wet color of the surface leaching layer A2is ash (Gleyl5/N), while dry color is powder (2.5Y7/1). The color in two status have reached the bleaching material color standard (chroma<2, wet brightness>3and dry brightness>6, or wet brightness>4and dry brightness>5). That is to say, the horizon can be set as bleached layer that we often say. In comparison, the wet color of deposited layer B2is red (10R4/8), while dry color is yellow brown10YR (-)5/6(-7.5YR5/). Soil quality water content, field capacity, maximum moisture, porosity all decrease with soil depth increases, and the soil bulk density, gravel content increase with soil depth increases. Soil aerates and soil loss has its special variation, which is soil aeration and the degree of loss in the bleached layer was significantly lower than that of other soil. Soil minerals in located research position are primary minerals e.g. quartz, feldspar minerals, failed to detect any number of clay minerals. Soil chemical process mainly started from surface soil (A1), because organic matter content, humus content, mineral element content in the horizon is always higher than other soil horizon in soil pedon. In the vertical profile, fulvic acids, with strong acid and activity, accounted for absolute advantage in humus compsiton. Silicon content is very low in the surface layer, but showed enrichment tendency in bleached layer (A2). Eluviation and deposition of soil profile substance analysis results showed that the silicon in the surface content is lower, but silicon showed enrichment trend in the bleaching layer. Although the soil in localization points has ashing deposition layer formed by humus complexometric leaching, chroma, lightness, saturation, and the content of activity Fe-Al do not satisfy the ashing deposition layer standard of real podzols on in Soil Taxonomy. Therefore, we classified such soil initially as bleached gray soil belonged to the Alfisols.(2) The interaction among soil temperature, moisture and energy cause the seasonal variation of soil water status. In the dry season (November and February), soil moisture of bleaching layer and deposited layer is very close during the November, and it showed soil water content of B2layer was lower than that of A2layer in February. In the rainy season, the soil water content of the B2layer significantly increased steadily due to soil solid water of A2layer of frozen melts and move down to B2layer, meanwhile soil quality water content of A2layer reduced and fluctuation. To the total soil quality water content, soil quality water content of A2layer were higher than those in B2layer of soil in each season. The highest soil quality water content of two soil horizon (i.e. A2and B2) occurs in the rainy season (August), minimum value appeared in the dry season (November and February). To soil temperature, A2horizon was demonstrated diurnal variation law that is first decreased then increased and decreased before soil water temperature reduce to freezing point, diurnal variation of soil temperature in deposition layer has smaller amplitude. In one year, soil temperature changes experienced two stages, one is the deposition layer is higher than that of bleached layers (B2>A2,22nd September-in the year April6th), lasting about7months. The second stage is bleached layer is higher than that of the deposition layer (B2<A2), this phase lasted for about5months. Soil water energy gradient leading by soil temperature leading causes soil water movement, which in June to September, soil water from the leached layer to layer deposition mobile, but the soil water has upward moveing trend after October. The freezing point calculated by soil soluble salt content and soil freezing and thawing results show that even if the soil temperature dropped to zero, the soil is not into the frozen, liquid soil water is forming crystal nucleus stage. Only the soil temperature temperature drops to freezing point and continuous cold, soil will be frozen. In located research soil, A2and B2common in freezing period time is50D (4.16-6.7)(including freezing and thawing process), common in the normal state of191D (6.13-12.24). The rest time in one year is A2or B2in the freezing period or normal state. The soil located normal state about half of year, only1/7.3time in soil freezing penetration status.(3) The existence form and content of iron, aluminium, manganese in maximum leached layer (bleached layer) and maximum deposition layer of bleached podzolic soil has obvious seasonal dry-rewet variation. During the rainy season (August and May), ferrous ions were significantly higher than ferric ion in soluble iron, and during the dry season (November and February), ferric ion content was significantly increased. But the seasonal monsoon and dry season changes did not affect the distribution of soluble iron and carbonate bound iron content between bleaching horizon and deposited horizon, i.e. soluble iron and carbonate bound iron content of the bleached layer was significantly lower than that of the deposited layer. This phenomenon is more intense in the rainy season; By contrast, humic qualitative state and iron with manganese state did not vary from season to season, but the content of deposition horizon is higher than that of leaching horizon. The distribution and mobile of typomophic element of soil (i.e. different forms of iron, aluminum, manganese) results indicates that there are two major chemical processes occurred in soil. One is the rinsing process, which iron, manganese was reduced and then leaching to the different soil layers; And the other is organic chelating leaching, which iron, aluminum leached wiht acid humus (mainly to fulvic acid) and other polyphenols. Although there are free aluminum in bleached layer also, free iron is more easily leaching wih humus acid chelate, and oxidized fixed in deposition layer. Free aluminum in soil more occurred in the exchange interaction. Therefore, soil chelate leaching is mainly dominanted by iron.(4) Litter leaf, about89.45%of total litter amount, is main litter in subalpine fir forest. The period of litter main return is concentrated in the9-11month, in the leaf litter and total litter amount60.32%,48.52%, respectively. Litter extract contains a variety of low molecular weight organic acid. Carboxylic acid such as formic acid was higher, and leading the type and content of low molecular weight organic acids in soil solution. In the same season, soil redox potentials in the A2layer were lower than those of B2layer. The formic acid and other low molecular weight organic acids, as well as having valence state of iron played a major role in soil redox system. Thus, in soil forming process of bleached podzolic, the mobile of low molecular weight organic acids and iron is the major redox reaction system and process, and strongly influences morphology and chemical characteristics formation of the leaching layer and depositing layer. The results of comparison different pH values of Eh indicated that Eh and pH values are suggested to be the most suitable method that coordinates representation. Microcosm control experiments show the linear regression relationship between soil redox potential and pH value, which can only be used as a reference value and has important significance when the field monitoring difficult or indoor assay is not reaction field real field case. The distribution of iron in different soil layer is closely related with soil redox potential changes. Soil of leaching layer is mostly in the restoring state in the dry and rainy seasons, due to high water content and anaerobic decomposition of organic matter. The oxidation reduction potential is relative low. Higher valence Fe is less; the vast majority is low redox state which has high solubility. Thus, Fe is easy to dissolve in organic acids produced by anaerobic decomposition of microorganism in surface soil, and move to subsoil in different forms. Different forms of low iron is oxidized into solid oxide or hydroxide (such as Fe2O3or Fe (OH)3) and then deposited in B2. The reason is that B2soil layer is in contact with the atmosphere than the opportunity for the soil of A2layer is less, the redox potential is high than A2, low valence iron is oxidized easily.These subsidence form a red or brown deposition layer including iron, aluminium, manganese common deposition. At the same time, aluminum silicate mineral was decomposed by organic acids, and then SiO2was ledved that forming a pale leached layer that SiO2relative enrichment. Notably, the color of bleached layer show a small amount of grey because soil of A2layer was mostly in the reduction state, a portion of the high iron is reduced to low iron Fe+compound, Fe2+usually pale green the leaching.(5) soil ammonium nitrogen, available potassium content of maximum leached layer (A2) and maximum deposition layer (B2) layer in the rainy season (August and May) was significant higher than that in the dry season (November and February), nitrate nitrogen is vice versa. During the rainy season, ammonia nitrogen, phosphorus, potassium in performance for the A2layer was significantly higher than that in B2layer, but in the dry season, their content of B2layer and A2layer was close, or the content of B2was significantly higher than that of A2layer. The content of soil organic carbon content in leached layer is greater than that in the deposition layer in each season. Soil total nitrogen, total phosphorus content in B2layer is higher than that of A2layer. Potassium, sodium and other mineral total amount change with the seasonal variation. During the rainy season, the leached layer above the deposition layer, while in dry season, deposited layer higher than the leached layer. Calcium, magnesium, copper, zinc, nickel and other mineral elements content did not change significantly in leaching and deposition horizon. In the process of soil organic matter moves down from the organic layer, bleached layers appeared transient accumulation due to anaerobic microbial activity and slower mineralization. Comprehensive analysis, bleached podzolic soil did not appear on serious impoverishment caused by ashing or rinsing. Ammonia nitrogen, nitrate nitrogen, available phosphorus available nutrients only changed with the seasonal variation of soil moisture. The results of soil nutrients in soil solution concentration have the same regular with above-metioned.更多还原