不同放牧强度下荒漠草原土壤有机碳及其δ~(13)C值分布特征

以内蒙古短花针茅荒漠草原为研究对象,通过测定不同载畜率下土壤部分理化性质、土壤有机碳含量和δ~(13)C值.探讨随放牧强度增加土壤有机碳深度分布和δ~(13)C值的组成差异特征.结果显示:随深度增加.有机碳含量呈线性急剧降低,变化范围在16.17～6.26 g/kg之间,而土壤有机碳的δ~(13)C值不断增大.变化范围在-22.5‰～-14.3‰.放牧对土壤有机碳的影响主要在0-20 cm土层,且放牧强度越大,有机碳含量越低,有机质分解程度越大,δ~(13)C值越偏正,δ~(13)C值的深度变化特征还表明.土壤剖面形成发育过程中当地气候和植被发生了很大的变化,可能实现了由C_4植物占优势向C_3植物占优势的变迁.     

荒漠草原土壤有机质碳稳定同位素特征研究

应用碳稳定同位素分析方法对内蒙古短花针茅荒漠草原土壤有机质及其δ13 C值垂直分布特征、表土δ13C值与建群种-短花针茅δ13 C值的相互关系进行分析,并测定土壤部分理化性质。结果显示:表土有机质含量变化范围为4.17～20.45g/kg;随深度增加,土壤有机碳(SOC)含量呈指数降低,其变化范围为17.98～1.39g/kg,而δ13C值则随剖面深度增加而明显富集,到75cm深度时δ13C值又迅速降低,变化范围为-26.38‰～-13.72‰,变幅>3‰,说明该地区气候和植被状况可能发生过剧烈变化;表土和植物δ13C值分馏程度较其它地区偏大,二者呈极显著相关(r=0.555,P<0.01),进一步说明地上植被状况是影响土壤有机质δ13 C值垂直分布特征的决定性因素。     

喀斯特地区坡地土壤有机碳的分布特征和δ^13C值组成差异

以喀斯特地区不同退化程度的两个典型坡地为研究对象,通过测定土壤部分属性与土壤有机碳含量的空间分布特征和δ13值,探讨土壤侵蚀和沉积过程中土壤有机碳(SOC)动态变化及影响因素。结果显示:自然坡地的表层土壤有机碳含量较高(6.3%~16.2%),δ13C值随着坡面向下逐渐降低,范围在-21.7‰~-14.3‰之间,变幅较大;撂荒坡地表层土壤有机碳含量为4.4%~7.4%,δ13C值在-21.4‰~-20.3‰之间,变幅相对较小。表明自然坡地沉积的新有机质要高于撂荒坡地,且两者δ13C值均与地表植被种类显著相关。另外,两个坡地各个地形部位的剖面土壤有机碳含量和δ13C值随深度变化,反映了植物残体的输入及在土壤中分解累积特征,有助于了解坡地土壤成土过程和受到的侵蚀程度。     

坡耕地黑土剖面有机碳的分布和δ13C值研究

以一东北黑土典型漫岗坡耕地为研究对象,通过测定不同地形部位(坡顶、坡肩、坡背、坡脚和坡足)部分土壤属性和δ13C值,探索土壤侵蚀和沉积对土壤有机碳(SOC)动态的影响。结果表明:表层土壤δ13C值与地形坡度、土壤粘粒含量、土壤含水量、pH值都显著相关。δ13C在土壤剖面中随深度变化,能够反映作物残体输入和土壤累积特征,有助于鉴定原始埋藏土壤表层。侵蚀部位土壤δ13C值与SOC含量线性拟合的倾斜角β与地形坡度成正相关,与粘粒含量成负相关,是反映SOC周转的一个良好指标。坡肩和坡背C3-C显著低于坡顶(对照点),C4-C含量无显著性差异,说明不同侵蚀程度的地形部位SOC含量差异主要是由C3-C引起;坡脚和坡足C4-C显著低于坡肩和坡背,说明沉积区新碳损失更大。     

不同母质发育土壤的中红外吸收光谱特征

选取湘东丘陵区四种典型母质发育土壤(酸性紫色土、花岗岩红壤、板岩红壤和第四纪红土红壤),采集剖面(深至母岩/母质层)样品,应用傅里叶变换红外光谱仪研究灼烧去除有机质处理、土层深度和母质类型对土壤中红外吸收光谱特征的影响,分析吸收光谱与土壤理化性质的关系。结果表明,去除有机质后,特征区的中红外吸收值升高,反映矿物质对红外吸收谱线的强烈影响。在剖面上,底土(60~80 cm或100~120 cm)的中红外吸收值高于表土(0~20 cm),与土壤有机质含量的剖面分布相反。四种土壤的中红外光谱均属典型的高岭石图谱。砂粒、粘粒含量与红外吸收值的相关性最好,砂粒含量的最大相关系数(0.51)出现在3700、913和720~540 cm~(-1)附近,粘粒含量的最大相关系数(0.54)出现在1100~694 cm~(-1);本研究表明,原土的中红外吸收光谱特征主要受矿物质的支配,可以很好地反映土壤质地的状况,指示土壤质量变化。     

陕西洛川全新世黑垆土理化特征年龄函数的构建

构建土壤理化特征年龄函数是定量认识土壤发育过程的重要途径,也是建立土壤发育模型的基础。本研究通过对陕西洛川全新世黑垆土剖面土壤理化特征及土壤14 C年龄进行研究,利用线性函数、对数函数和三阶多项式对其进行拟合,从而构建土壤年龄函数。结果表明:利用三阶多项式对土壤黏粒(<0.002mm)、粉粒(0.002～0.02mm)、砂粒(0.02～2mm)与土壤年龄拟合效果最好,其变化趋势表明了黑垆土层的存在;而对数函数的拟合结果较好地反映了土壤有机碳随土壤年龄逐渐减少和pH随土壤年龄逐渐增大的过程;土壤CaCO3含量、Mn/Zr,Fe/Zr,K/Zr,Mg/Zr,Ca/Zr,P/Zr,Na/Zr随土壤年龄变化规律与三阶多项式拟合结果最为相符,其结果较好地反映了CaCO3与各种土壤元素在土壤中的迁移过程。     

可变电荷土壤的有效阳离子交换量及其在分类上的应用

通过对亚热带地区第四纪红土发育的14个土壤剖面的52个样品的分析,比较研究了土壤有效阳离子交换量ECEC和CEC及土壤粘粒、pH、有机质含量等的关系,介绍了有效阳离子交换量在土壤分类上的初步应用。     

滇东山原红壤退化过程中的土壤剖面有机质与养分变异

山原红壤是云贵高原广泛发育的一种地带性古土壤,近年来退化严重,为了解山原红壤退化过程,采用"以空间换时间"的思路,对云贵高原山原红壤区同一区域林地、灌丛、草地和裸地土壤剖面养分含量进行对比分析。结果表明:从能生长植被的山原红壤至多年难以生长植被的"红裸土",土体平均有机质含量呈灌丛草地林地裸地的变化趋势;灌丛和草地土壤有机质含量随剖面深度递增而降低,裸地和林地土壤削面有机质含量没有明显的垂直变化规律;与有植被覆盖的各土体相比裸地的硝态氮、铵态氮和速效钾剖面含量具有特殊性,硝态氮含量随剖面深度的递增明显减小,铵态氮含量随剖面深度的递增而增大;随着植被的退化,土壤有机质与养分的相关性大致呈减弱趋势,灌丛的土壤有机质与养分的相关性最强,裸地土壤有机质与养分相关性最弱。     

δ13C方法在土壤有机质研究中的应用

δ13C方法是近年来用于土壤有机质动力学研究的一种新方法,该方法除了具有14C标记法的优点外,还具有无放射性,可以提供长期的标记,并能使所有的土壤有机质组分都能被均匀标记,相对经济、在实验地采样后直接进行研究等特殊优点,从而在土壤有机质及其组分的来源、周转和C3/C4植被的历史变化研究中得到广泛应用。随着该方法的迅速发展以及各种分析δ13C值技术的不断改进,δ13C方法在研究土壤过程特别是土壤碳循环中显示出新的活力。为了推动δ13C方法在国内土壤有机质研究中的应用,本文对影响土壤有机质δ13C值的因素、国内外近年来该方法在土壤有机质研究中的应用和δ13C值的分析方法作了较全面的综述。     

南极半岛海洋气候区的土壤Ⅶ. 矿物学特性

南极海洋气候区岩石风化和土壤形成过程中有明显的原生矿物蚀变作用和自生矿物成矿作用。本文以粗骨寒冻灰化土和石灰性扰动冻土两种有代表性的土壤类型为例,阐述了本区土壤矿物学特征。指出铝氧化物、绿泥石、碳酸盐是本区玄武岩类风化物质上发育土壤中的主要自生矿物类型,蒙脱石、特别是绿泥-蒙脱石混层矿物是南极海洋气候区土壤粘粒部分的特征矿物。不同土壤由于成土环境、成土过程、成土历史的差异,其土壤物质的矿物学组成、含量、形态、分布具有明显不同。土壤发生性铁氧化物与成土作用和土壤过程密切相关,其矿物类型、含量、形态特征、分布模式在不同的土壤中明显不同,是表征土壤发育程度与剖面形态表达的有效指标。     

Relating the biological stability of soil organic matter to energy availability in deep tropical soil profiles

Tropical subsoils contain large reservoirs of carbon (C), most of which is stored in soil organic matter (SOM). Subsoil OM is thought to be particularly stable against microbial decomposition due to various mechanisms and its position in the soil profile, potentially representing a long-term C sink. However, few experiments have explicitly investigated SOM stability and microbial activity across several orders of magnitude of soil C concentrations as a function of soil depth. The objective of this study was to evaluate the biological stability of SOM in the upper 1.4 m of tropical forest soil profiles. We did so by measuring CO₂ evolution during a 90-day laboratory incubation experiment on a sample set that was previously characterized for C and nutrient concentrations and microbial biomass. We concurrently measured the energy content of SOM using differential scanning calorimetry (DSC) as an index of the energy available for microbial metabolism, with the hypothesis that the biological stability of SOM would be inversely related to the energy contained within it. Cumulative CO₂ evolution, mean respiration rates, and the energy density of SOM (energy released during combustion normalized to soil C) all declined with soil depth (P < 0.01). Biological indices of C stability were well correlated with measures of SOM energy. There was no change in the mean respiration rate as a function of depth when normalized to soil C, and a trend toward increased respiration per-unit microbial biomass (P = 0.07). While reduced microbial respiration in subsoils suggests an increase in the biological stability of SOM, we suggest this is driven principally by concurrent declines in energy availability as measured by DSC and the size of the microbial biomass pool. On a per-unit biomass basis, subsoil OM may be as prone to decomposition and destabilization as surface SOM.     

种植苹果树对渭北果园土壤胶结物质分布的影响

本研究通过系统研究种植果树对土壤胶结性物质的演化规律及其与土壤团聚体稳定性之间关系的影响,探索影响果园土壤团聚体状态的因素,以期为果园科学管理提供理论依据。在渭北旱塬苹果主产区分别选取10 a、20 a的苹果园和农田(冬小麦-夏玉米轮作,对照)各4个,在果树冠层投影范围内距树干2/3处逐层采集0~100 cm土层土壤样品和0~50 cm土层原状土壤样品,研究不同植果年限果园及农田土壤剖面黏粒、有机质、CaCO_3等团聚体胶结物质的分布及其与团聚体稳定性之间的关系。结果发现:在0~100 cm土层范围内,各果园土壤黏粒含量基本随土层深度的增加而递增,且在0~40 cm土层表现为农田10 a果园20 a果园,40 cm以下土层则呈现相反的态势;种植果树相比农田可显著增加0~100 cm土层土壤有机质总储量,但随着种植果树年限的增加,土壤有机质总储量呈递减趋势;在0~100 cm土层土壤CaCO_3总储量表现为10 a果园农田20a果园,但在0~40 cm土层CaCO_3含量及储量表现为10 a果园农田20 a果园,而40~100 cm土层则为20 a果园10 a农田。皮尔森相关分析发现(29)0.25 mm土壤团聚体的数量和平均重量直径(MWD)与土壤黏粒、有机质和CaCO_3含量密切相关,其中机械稳定性团聚体的数量和稳定性主要受土壤中CaCO_3、有机质含量的影响,水稳性团聚体的数量和稳定性主要受土壤中黏粒和CaCO_3的影响。总之,植果显著改变了土壤中黏粒、有机质、CaCO_3的演化过程和趋势,随植果年限增加,果园土壤黏粒和CaCO_3在土壤较深土层淋溶淀积明显;各果园土壤有机质总储量虽然高于农田,但随植果年限增加,有逐渐减少的趋势。可见植果明显加速了渭北黄土塬地土壤的残积黏化和钙化过程,影响着表层土壤团聚作用和底层土壤的紧实化和坚硬化程度。     

喀斯特坡地浅层岩溶裂隙土壤团聚体稳定性与养分垂向变化特征

浅层岩溶裂隙（SKF）为植物提供生长空间、水分和养分,是石漠化地区的重要生境类型。以矩形和漏斗形SKF剖面为研究对象,采用干、湿筛分法和Le Bissonnais法,分析了不同土层土壤团聚体稳定性特征和破坏机理,测定了团聚体中土壤有机质（SOM）、碱解氮（AHN）和有效磷（AP）的含量。结果表明：SKF剖面粒径＞0.25 mm的团聚体均超过90%,PAD值范围为0.01%~4.75%。干、湿筛作用下,MWD值变化范围分别为4.63~7.69 mm和1.33~4.24 mm,团聚体分形维数D范围分别为1.57~2.18和1.55~2.15。SKF土壤团聚体的稳定性随剖面深度加深而降低,矩形SKF土壤团聚体的稳定性要强于漏斗形SKF,快速湿润产生的消散作用是造成团聚体破碎的主要机制。团聚体破坏率（PAD）、团聚体分形维数（D）和平均重量直径（MWD）这三类指标均表明,SKF土壤团聚体水稳定性、通透性均较好。SKF剖面30 cm以下土层,团聚体SOM、AHN和AP含量相较0~20 cm土层大幅下降,含量范围分别为13.27±0.94~37.53±3.47 g?kg-1、71.58±3.27~198.54±22.63 mg?kg-1和0.15±0.03~ 0.38±0.10 mg?kg-1,土壤AP十分贫乏。SKF形态会影响SOM含量随土层深度的变化,矩形SKF 30 cm以下土层含量随深度加深而降低,而漏斗形SKF则没有显著性差异。随土层深度加深,矩形和漏斗形SKF剖面AP含量的变化趋势一致,AHN含量的变化趋势则与SKF形态之间没有明显关联。SOM、AHN和AP含量越高,SKF剖面团聚体水稳定性越强。     

Black carbon in the zonal steppe soils of Russia

Black Mollisols are typically rich in charred organic matter, however, little is known about the zonal distribution of black C (BC) in steppe soils. In this study, we used benzene polycarboxylic acids (BPCA) as specific markers for BC in particle‐size fractions of depth profiles in several zonal soils (Greyzem, Phaeozem, Chernozem, Kastanozem) of the Russian steppe. In addition, liquid‐state ¹³C‐NMR spectra were obtained on the alkaline‐soluble soil organic matter (SOM). The results showed that both the content and depth distribution of BC varies in the different soil types; the concentration of BC in the bulk top soils being closely related to the aromaticity of the SOM (r² = 0.98 for the native topsoils, 0.83 for top‐ and subsurface soils). Especially the Chernozems were rich in aromatic SOM, which partly contained more than 17% BC of total C, most of which being allocated in the mineral fractions. Long‐term arable cropping did not reduce the BC contents of the surface soil, though it did promote the enrichment of BC in the silt fractions. The same shift was detected as soil depth increased. We conclude that BC is not fully inert in these soils, but apparently can be preserved in the silt as decomposition of SOM increased, i.e., it accumulates exactly in that fraction, which has been formerly assigned to contain old, aromatic C.     

Carbon isotopes of water‐extractable organic carbon in a depth profile of forest soil imply a dynamic relationship with soil carbon

Although considerable research has been conducted on the importance of recent litter compared with older soil organic matter as sources of dissolved organic carbon (DOC) in forest soils, a more thorough evaluation of this mechanism is necessary. We studied water‐extractable organic carbon (WEOC) in a soil profile under a cool‐temperate beech forest by analysing the isotopic composition (¹³C and ¹⁴C) of WEOC and its fractions after separation on a DAX‐8 resin. With depth, WEOC became more enriched in ¹³C, which reflects the increasing proportion of the hydrophilic, isotopically heavier fraction. The ¹⁴C content in WEOC and its fractions decreased with depth, paralleling the ¹⁴C trend in soil organic matter (SOM). These results indicate a dynamic equilibrium of WEOC and soil organic carbon. The dominant process maintaining the WEOC pool in the mineral soil appears to be the microbial release of water‐soluble compounds from the SOM, which alters in time‐scales of decades to centuries.     

红壤水稻土肥力性状的演变特征

大田条件下 ,通过选点采样分析 ,研究了不同利用年限红壤水稻土的物理、化学和生物学性质的动态变化特征。荒地红壤水耕利用后 ,土壤颗粒组成呈现规律性变化 ,粘粒 (<0 0 0 2mm)含量从荒地红壤的 3 9%下降到 80a稻田土壤的 1 7% ,而粉砂 (0 0 2～ 0 0 0 2mm)含量升高。土壤pH一般增加 0 5～ 1个单位 ;0～ 1 0cm土壤有机碳和全氮含量从荒地红壤的 4 5 8gkg- 1和 0 3 9gkg- 1增加到 3 0a红壤稻田的1 9 6gkg- 1和 1 62gkg- 1,其后 ,即使利用时间长达 80a ,土壤有机碳和全氮含量并没有显著差异 ;土壤全磷含量 ,经 3a水耕利用后可从荒地红壤的 0 5gkg- 1提高到 1 3gkg- 1,表明通过施肥可使红壤磷素快速积累 ;而在水耕利用过程中 ,红壤稻田土壤的钾素含量呈下降趋势 ,经 80a利用的红壤稻田 ,0～ 1 0cm土壤钾素含量仅为荒地红壤的 80 % ;全铁和游离铁的含量也呈下降趋势。随着水耕熟化过程 ,细菌数量和脲酶活性也明显升高。不同利用年限红壤稻田土壤的各项性状指标的变化结果还表明 ,荒地红壤水耕利用后要达到高度熟化的稻田土壤肥力水平 ,需要经过 3 0a的时间     

秸秆碳的田间原位分解和微生物量碳的周转特征

应用14 C示踪技术研究了杂交狼尾草秸秆在稻麦轮作田中为期 1年的原位分解。结果表明 :秸秆用量对其分解率影响甚微 ,1年后秸秆C分解了 72 %左右 ,分解速率常数为 2 7× 1 0 - 3d- 1,但秸秆用量的多少与土壤原有碳的分解和土壤有机碳平衡密切相关。黄棕壤原有C年分解率为 5 4 5 %～ 6 0 7% ,分解速率常数在 1 0 4× 1 0 - 4～ 1 1 8× 1 0 - 4d- 1之间。随秸秆用量增加 ,黄棕壤原有C分解率和分解量均增加 ,土壤有机碳的亏缺减少。微生物量14 C占加入秸秆14 C的 3 79%～ 1 0 63% ,占土壤残留14 C的 1 2 2 7%～1 7 4 3% ,其大小变化及减少程度均较微生物量12 C显著。微生物量12 C约为微生物量14 C的 0 74～ 3 85倍 ,说明大多数情况下 ,土壤原有C仍是土壤微生物活动所需能量和养分的主要来源。微生物量14 C的周转率在 1 1 0～ 1 1 8a- 1之间 ,微生物量12 C的周转率在 0 97～ 1 0 6a- 1之间。增加秸秆用量可加快土壤微生物量C的周转速度 ,反过来微生物量C周转速度的加快又加速了秸秆C和土壤原有C的分解。土壤原有C和秸秆C的分解进程与微生物量12 C和微生物量14 C的动态变化趋势一致 ,说明有机碳分解的快慢是土壤微生物活动强弱的外在表现。     

Black carbon contribution to soil organic matter composition in tropical sloping land under slash and burn agriculture

Tropical soils are generally depleted in organic carbon (OC) due to environmental conditions favouring decomposition and mineralisation of soil organic matter (SOM). In Northern Laos, sloping soils are subjected to slash and burn agriculture, which leads to production of black carbon (BC), a stable SOM fraction. BC may directly influence the quantity and quality of SOM sequestered in tropical soils. The aim of this study was to quantify BC content and evaluate its impact on the chemical and stable isotope composition of SOM along a catena composed of Dystrochrepts at the bottom of the slope, Alfisols (midslope) and Inceptisols at the top of the slope for different burning frequencies. Six soil profiles, situated on a slope ranging from a river bank to the summit of a hill, were sampled. The stable isotope compositions (¹³C and ¹⁵N) of samples from both organo-mineral A and mineral B and C horizons were determined. The chemical composition of SOM analysed by ¹³C CPMAS NMR spectroscopy and the contribution of BC determined by dichromate oxidation were compared to OC and iron oxide content as well as land management including the burning cycle.The highest C contents were recorded at midslope positions. At any position on the slope, δ¹³C and δ¹⁵N ratios showed an enrichment in ¹³C and ¹⁵N with increasing soil depth. The OC content of soil horizons was related to their aryl C content, which is the component most likely driven by BC inputs. The BC contributions analysed by dichromate oxidation ranged from 3% to 7% of total OC. A positive correlation was obtained between aryl C and the BC content of SOM. Comparison of BC content and stable isotope composition of SOM showed that BC influenced the δ¹³C and the δ¹⁵N stable isotope ratios of these soils. BC was not associated with the mineral phase. The highest BC contents were measured under intensive slash and burn practice in the vicinity of the boundary of Alfisols at the top of the slope, where erosion was severe. Therefore, BC, a SOM component strongly influencing OC sequestration of these soils, is susceptible to translocation down the slope.     

Predicting soil organic matter stability in agricultural fields through carbon and nitrogen stable isotopes

In order to evaluate the sustainability and efficiency of soil carbon sequestration measures and the impact of different management and environmental factors, information on soil organic matter (SOM) stability and mean residence time (MRT) is required. However, this information on SOM stability and MRT is expensive to determine via radiocarbon dating, precluding a wide spread use of stability measurements in soil science. In this paper, we test an alternative method, first developed by Conen et al. (2008) for undisturbed Alpine grassland systems, using C and N stable isotope ratios in more frequently disturbed agricultural soils. Since only information on carbon and nitrogen concentrations and their stable isotope ratios is required, it is possible to estimate the SOM stability at greatly reduced costs compared to radiocarbon dating. Using four different experimental sites located in various climates and soil types, this research proved the effectiveness of using the C/N ratio and δ¹⁵N signature to determine the stability of mOM (mineral associated organic matter) relative to POM (particulate organic matter) in an intensively managed agro-ecological setting. Combining this approach with δ¹³C measurements allowed discriminating between different management (grassland vs cropland) and land use (till vs no till) systems. With increasing depth the stability of mOM relative to POM increases, but less so under tillage compared to no-till practises. Applying this approach to investigate SOM stability in different soil aggregate fractions, it corroborates the aggregate hierarchy theory as proposed by Six et al. (2004) and Segoli et al. (2013). The organic matter in the occluded micro-aggregate and silt & clay fractions is less degraded than the SOM in the free micro-aggregate and silt & clay fractions. The stable isotope approach can be particularly useful for soils with a history of burning and thus containing old charcoal particles, preventing the use of ¹⁴C to determine the SOM stability.