Biogeochemical interfaces in soil: The interdisciplinary challenge for soil science

Soil, the “Earth's thin skin” serves as the delicate interface between the biosphere, hydrosphere, atmosphere, and lithosphere. It is a dynamic and hierarchically organized system of various organic and inorganic constituents and organisms, the spatial structure of which defines a large, complex, and heterogeneous interface. Biogeochemical processes at soil interfaces are fundamental for the overall soil development, and they are the primary driving force for key ecosystem functions such as plant productivity and water quality. Ultimately, these processes control the fate and transport of contaminants and nutrients into the vadose zone and as such their biogeochemical cycling. The definite objective in biogeochemical‐interface research is to gain a mechanistic understanding of the architecture of these biogeochemical interfaces in soils and of the complex interplay and interdependencies of the physical, chemical, and biological processes acting at and within these dynamic interfaces in soil. The major challenges are (1) to identify the factors controlling the architecture of biogeochemical interfaces, (2) to link the processes operative at the individual molecular and/or organism scale to the phenomena active at the aggregate scale in a mechanistic way, and (3) to explain the behavior of organic chemicals in soil within a general mechanistic framework. To put this in action, integration of soil physical, chemical, and biological disciplines is mandatory. Indispensably, it requires the adaption and development of characterization and probing techniques adapted from the neighboring fields of molecular biology, analytical and computational chemistry as well as materials and nano‐sciences. To shape this field of fundamental soil research, the German Research Foundation (DFG) has granted the Priority Program “Biogeochemical Interfaces in Soil”, in which 22 individual research projects are involved.     

Modeling of the evolution of steppe chernozems and development of the method of pedogenetic chronology

Geoarchaeological methods were used to study chronosequences of surface soils in the steppe zone and to trace soil evolution during the Late Holocene in northwestern Crimea. It was found that the morphological and functional “maturity” of the humus horizons in steppe chernozems of the Late Holocene was reached in about 1600–1800 yrs. After this, their development decelerated irreversibly. The maximum concentration of trace elements accumulated in these horizons in the course of pedogenesis was reached in 1400 yrs. A new method of pedogenetic chronology based on the model chronofunction of the development of irreversible results of pedogenesis over time is suggested. Original pedochronological data and growth functions—the most suitable models for simulating pedogenesis over the past three thousand years—suggest that the development of morphological features of soil as an organomineral natural body follows growth patterns established for biological systems.     

Die Schwarzerden Nordostdeutschlands und ihre Stellung in der holozänen Landschaftsentwicklung

Phaeozems of northeastern Germany and their position in holocene landscape development A typical soil association of NE-German young moraine area (Uckermark-region) including Phaeozems and colluvial deposits (Cumulic Anthrosols) was described macromorphologically using a trench profile and investigated by chemical standard analyses, humic compound analysis, pollen analysis and ¹⁴C-radiocarbon dating. Results are discussed in view of pedogenesis of Phaeozems. Conclusions were made concerning the holocene premedieval landscape development. A key position for reconstructing palaeoecological environmental conditions is held by “Black colluvium”. The “Black colluvium” is the relocated humous horizon of former Chernozems influenced by syn- and postsedimentary processes. The specific character of holocene landscape development and pedogenesis of the Uckermark-region is connected with the special natural conditions and history of land-use.     

The regularities of the late Holocene soil formation in the lower don steppes

The direction and stages of pedogenesis, rate and scales of changeability, and type of evolution of chernozems in the steppes of the Lower Don are ascertained by studying the archaeological monuments of the Bronze Age, Early Iron Age, and Middle Ages. It is shown that the soil formation process was characterized by cyclicity, and evolutional soil transformations took place at the level of subtype. The paper ascertains the polygenetic character of modern chernozems, whose evolution during the second half of the Holocene was predominantly low-contrast, inheriting, and transforming. The processes forming the humus, salt, gypsum, and carbonate profiles, as well as the processes of solonetzization-desolonetzization, were the most dynamic. The fundamental differences in the genesis of different parts of the humus profile are revealed. The role of climatically pulsing solonetzicity in forming the specific Azov chernozems is for the first time ascertained.     

Aluminum complexation suppresses citrate uptake by acid forest soil microorganisms

Organo-mineral interactions have been hypothesized to play a major role in biogeochemical cycling and pedogenesis in some forest soils. These processes are likely to be controlled to some extent by their persistence in soil, however, the factors regulating their bioavailability remain poorly understood. Therefore, we investigated the microbial utilization of ¹⁴C-labeled citrate in glass bead filled bioreactors containing a biofilm developed from an inoculum from an acid forest soil. The removal of Al-citrate in the bioreactors was negligible compared to the rate of citrate removal in the absence of Al. There was no evidence that in the short-term the microbial community adapted to increase the utilization of Al-citrate. In bioreactors filled with a Picea abies forest soil (Haplic Arenosol) the rates of citrate utilization were always slightly higher than that of Al-citrate. We conclude that complexation of citrate by metals such as Al may have a significant effect on their role in soil biogeochemical cycles.     

腐殖物质特异性及其产生机制

腐殖物质(HS)是天然有机质的主体,其组成、结构十分复杂。之所以称其为一类物质,就是基于他们具有不同于其形成前体的化学组成与结构特征的共性,或称"特异性",即在腐殖化过程中形成新的化学组合,甚至是"特异的"结合方式。但经历近200年的探索,人们对这种"特异性"的认识仍然不清楚,并缺少实验上的证据。加之近几年,一些研究结果被不适当的推演,HS的"特异性"更加受到质疑。HS到底有无"特异性"?"特异性"是什么?这涉及HS生物化学的根基,必须进行深入研究和回答。本文对已有的一些研究报道,包括HS的特异性、生物分子单体与HS结构特征的比较、基于生物多样性(进化)的天然生物材料与HS形成、HS形成机理及胡敏酸(HA)、富里酸(FA)形成顺序、矿物黏粒催化与HS形成、异核单量子相干谱(HSQC)和总相关谱(TOCSY)、傅里叶变换离子回旋共振质谱(FT-ICR-MS)和C1s软X射线近边吸收精细结构(NEXAFS)同步辐射技术应用等进行综合评述,并提出HS化学进一步研究的方向。     

土壤时空变化研究的进展与未来

理解和表征土壤的时空变化是土壤学的基本任务,也是评估和合理发挥土壤功能的重要前提。土壤的时空变化与气候环境变迁、岩石圈风化、地表物质迁移、生物地球化学循环等圈层变化过程相耦合。围绕土壤时空变化研究的新近进展,本文综述并展望了土壤形成和演变过程、土壤形态学、土壤调查、土壤分类、数字土壤制图与土壤退化的发展态势。未来土壤时空变化研究的关键科学问题主要包括:地球表层系统中土壤与环境要素之间的多过程耦合机理与模拟、多尺度土壤-环境关系与模拟、多元土壤信息的融合机理与数据同化。未来重点研究领域将涉及到关键带科学引领的土壤形成和演变研究、多尺度数字土壤制图与时空变化预测、基于多传感器的土壤综合观测原理与技术、完整和详尽的国家和全球土壤资源清单及共享平台建设、区域土壤资源退化机理及其功能恢复。     

Evolution of forest pedogenesis in the south of the forest-steppe of the Central Russian Upland in the Late Holocene

The Late Holocene stage of forest pedogenesis has been studied on the interfluves along river valleys in the forest-steppe zone of the Central Russian Upland. The development of gray forest soils from the former chernozems as a result of the Late Holocene advance of forest vegetation over steppes is discussed. It is argued that the climatic conditions of the Subatlantic period were unstable, so that multiple alternation of forest and steppe vegetation communities took place. This specified a complex character of soil evolution upon contrasting substitution of forest pedogenesis for steppe pedogenesis. On the interfluves near the natural drainage network (balkas, ravines, and steep slopes of river valleys), the climate-driven dynamics of forest and steppe vegetation with corresponding changes in the character of pedogenesis could take place during the entire Holocene, which is reflected in a lower thickness of humus profiles and deeper leaching of carbonates from chernozems of the Early Iron Age in comparison with their analogues formed under steppe cenoses in central parts of the interfluves. Two variants of the evolution of gray forest soils can be suggested: the pulsating evolution typical of balkas and interfluves near river valleys and the continuous progressive evolution typical of automorphic (plakor) positions in central parts of the interfluves.     

Proteins as Agricultural Polymers for Packaging Production

Advantages, types, formation, and properties of agricultural packaging materials based on proteins, with examples, are reviewed in detail. Proteins have long and empirically been used to make biodegradable, renewable, and edible packaging materials. Numerous cereal and vegetable proteins (such as corn zein, wheat gluten, and soy proteins) and animal proteins (such as milk proteins, collagen, gelatin, keratin, and myofibrillar proteins) are commonly used to form agricultural packaging materials. Two technological processes have been investigated to make materials based on proteins: the “wet (or solvent) process” based on dispersion or solubilization of proteins in a solvent medium, and the “dry process” based on the thermoplastic properties of proteins under low water content conditions. The macroscopic properties (including solubility in water, mechanical properties, and barrier properties) of agricultural packaging materials based on proteins are dependent mainly on the structure of the macromolecular three-dimensional network and on interactions between proteins, plasticizers, and cross-linking agents.     

南极半岛海洋气候区的土壤Ⅴ.气候变化响应

气候变化导致南极海洋气候区冰川消退、多年积雪融化,为新的土壤形成与分布提供了潜在的母质基础与发展空间;地表和土壤内部水分活动在时间和空间上的加强促进了以自由水为基础的土壤过程和冰缘地貌过程;由气候变化引发的低等植物生境、群落结构变化、初级生产力与生物量的提高、海洋脊椎动物迁徙和栖息地的变迁,影响了本区土壤有机质积累过程以及土壤有机质结构与性状。已有的证据表明,气候变化正对南极海洋气候区土壤发生、发育及演变产生重要影响。     

Towards Establishing the Age,Location, and Identity of the Inert Soil Organic Matter of a Spodosol

An interlayer clay-organic complex has been isolated from a near-surface horizon of a recent Spodosol from New Zealand. Treatment with hydrogen peroxide selectively removed the organic material attached to external clay surfaces. The radiocarbon age of the treated complex, determined by accelerator mass spectrometry, was 6716 ± 524 years B.P. Since this value refers to the interlayer organic species which has been completely protected against microbial attack, and contamination by “young” carbon, it may be regarded as the “true” age of the soil, that is, the starting point of humus formation and pedogenesis. The interlayer organic carbon comprised approximately 13 percent of the total carbon in the soil horizon. We propose that a biologically inert organic matter (IOM) fraction may be isolated from most soils as this fraction is commonly associated with clay-size particles. Evidence is also accumulating to indicate that IOM is dominantly composed of polymethylenic structures, probably derived from natural waxes, and aliphatic biopolymers present in protective layers of vascular plants.     

Complex pedogenesis of ferrallitic savanna soils in South Sudan

Complex pedogenesis in ferrallitic savanna soils is demonstrated by means of three typical profiles. The information provided includes relative age relationship of soils on the polycyclic pediment slopes, macro- and micromorphological characteristics, some chemical and complete mineralogical data. The authors compare the operation of basic processes of saprolitization (kaolinization, primary mottling) and pedogenesis (homogenization, local, vertical and lateral redistribution of iron) in forest soils formed on deep saprolite, and savanna soils on generally much shallower saprolite. Complex pedogenesis in the latter results from intermittent erosional impact, changes of climate and the stepwise downward weathering and deepening of the solum. All of these factors cause (homo- or heterogenetic) changes of internal hydrological conditions in the whole or parts of the solum. By means of detailed differentiation of ferruginous precipitates in regard to their crystal form (hematite and goethite) and their successive formation and alteration, the authors attempt to elucidate the history of soil formation.     

土壤排水系统在土壤演变中的作用

While research on pedogenesis mainly focuses on long-term soil formation and most often neglects recent soil evolution in response to human practices or climate changes, this article reviews the impact of artificial subsurface drainage on soil evolution. Artificial drainage is considered as an example of the impact of recent changes in water fluxes on soil evolution over time scales of decades to a century. Results from various classical studies on artificial drainage including hydrological and environmental studies are reviewed and collated with rare studies dealing explicitly with soil morphology changes, in response to artificial drainage. We deduce that soil should react to the perturbations associated with subsurface drainage over time scales that do not exceeding a few decades. Subsurface drainage decreases the intensity of erosion and must i) increase the intensity of the lixiviation and eluviation processes, ii) affect iron and manganese dynamics, and iii) induce heterogeneities in soil evolution at the ten meter scale. Such recent soil evolutions can no longer be neglected as they are mostly irreversible and will probably have unknown, but expectable, feedbacks on crucial soil functions such as the sequestration of soil organic matter or the water available capacity.     

Nature of an overlapped paleosol and its significance in pedogenesis and paleogeography in North Huai region, China

An overlapped paleosol (albic Paleudalf) in North Huai region was studied by means of sand and clay mineralogy, elemental geochemistry, particle size distribution, observation of quartz sand surface structure under SEM, micromorphology, pollen analysis as well as soil dating. These albic soils are very extensive on uplands in this region and the profiles have developed on two individual formations rather than being differentiated by the homogenous eluvium of gneiss. It was also indicated that the soil evolution in this region proceeded from dessication and kaolinization during the middle Pleistocene to accumulation of bases and predominance of fragmental minerals in the early Holocene. The pedogenesis was further related to climate-landscape events in this region during the Quaternary. This study advocated that awareness of soil-landscape evolution was necessary in advance of pedogenesis research and a single soil-forming process could not account perfectly for soil formation with delicate evolution history.     

土壤起源与宜居地球的形成

在各种成土因素交互作用下,地球土壤起源和演变历经变化的环境和多种成土过程。研究表明最早的古风化壳出现在太古宙;而随着地球生物演进,生物因素加入风化成土作用与成土过程,土壤学家眼中的土壤形成、发育于寒武纪。漫长的地质历史时期不同的成土环境发育有各种类型土壤,这些土壤发育与演化过程又反作用于景观、地形、生态系统、气候系统,改变大气成分组成和地球化学循环,影响、反馈、调节全球或地区的表层系统,土壤圈的形成是宜居地球形成的重要标志。     

Roles of iron and clay in Genesis of acid soils under a humid,temperate climate

The occurence of acid brown soils, podzols and podzolic soils, and the intermediate types of ochreous brown and brown podzolic soils over arenaceous granite in Vosges was closely correlated with the contents of iron rather than with calcium plus magnesium in the parent materials. Acid brown soils were associated with high and podzols and podzolic soils with low contents of iron, the limiting value being near 5 percent. Additional investigations in beech forests of soils derived from a variety of acid rocks indicated that contents of iron and clay in the parent materials controlled the type of humification of litter. With higher contents of iron and clay, humification gave rise to mull. With lower contents, mor or moder was formed. The nature of humification was believed responsible for tilting pedogenesis toward brunification or toward podzolization. In brunification, the clay-iron-humus complexes that are formed tend to be immobile and promote formation of crumbly structure. The “active iron” occurs as films around clay particles and thus links them to humus. In podzolization, on the other hand, the complexes formed are of humus with iron or aluminum but without clay. These are mobile and are translocated downward in profiles to form spodic horizons. The organo-metal complexes in ochreous brown and brown podzolic soils are mobile to only a limited extent. The combined results of these investigations demonstrate that contents of iron and clay rather than calcium in parent materials determine the pathway of pedogenesis from acid rocks under humid, temperate climates.     

甘肃东部地区黑垆土的发育演化模式与发生学特性的时空差异

本文研究了甘肃东部(亦称陇东)黄土塬区黑垆土的发育演化模式及成土速率与成土作用强度的时空变异规律。提出黑垆土叠加剖面的形成依次经历了古土壤发育、新冰期黄土粉尘堆积覆盖、人类耕作堆肥熟化三个阶段。埋藏古土壤普遍形成于距今7500-3500年高温期的温湿草原环境中,南部粘化黑垆土带还存在距今约13800-7500年的古土壤发育阶段,但此时的成土速率比中全新世小。同一阶段的成土速率和成土作用的强度南部比北部大。在新冰期(距今约3000-2500年)中黄土粉尘的加速堆积,是古土壤层被掩埋以及形成覆盖层的直接原因。具有普遍性的人为耕作熟化是在全新世黄土覆盖层上进行的,黑垆土剖面中不可能普遍存在古耕层。     

The Mississippian Paleosols in the Brontsy Quarry,Kaluga region

A chronosequence of five Visean (Aleksinian–Venevian interval, C1v, 326–336 Mya) paleosols on the territory of Moscow calcareous sedimentary basin (Brontsy quarry, Kaluga region) was studied in detail. Two lowermost paleosols are coastal peat-bearing paleosols developed under mangrove vegetation. Three upper paleosols develop pedocomplexes, in which the lower part is the marine limestone altered to different degrees by weathering/pedogenesis with the formation of eroded Rendzina-type soil. It is overlain by paleosols developed from terrigenous sediments of playa origin. They are characterized by elevated concentrations of Fe, Mg, Ti, Ga, and some other elements; the formation of secondary micritic carbonates, iron oxides, and smectites; and increased values of geochemical indexes (such as CIA-K). Smectite (low-charged beidellite) predominates in these paleosols. Iron oxides are represented by goethite and lepidocrocite attesting to the predominance of oxygenic environments. Pedocomplex at the Mikhaylovian/Venevian boundary is overlain by non-marine palustrine deposits known as “black rhizoidal limestone.” The paleoclimate reconstruction based on the chemical composition data attests to its polycyclic character. The Mikhaylovian time was most humid was (~1000 mm/yr). Later, starting from Venevian, gradual aridization of the climate began and annual precipitation decreased to 750 mm/yr and less.     

Vegetation and pedogenesis on pyrogenic substrates of former peat soils

The role of vegetation and chemical factors in the development of the primary pedogenesis and evolution of pyrogenic formations resulting from fires on drained peat soils was studied. Over four years after the fire, a shallow (1 cm) humus horizon is formed on the surface of the ashy horizon of the pyrogenic formations. For six years, its thickness increases up to 3–4 cm. The dynamics and productivity of the plant cover on the pyrogenic formations were investigated. The dominant plant species were restricted to certain pyrogenic formations. The formation of stable phytocenoses and chemical transformation of substrates are the factors governing the primary pedogenesis on pyrogenic substrates. Four stages in the evolution of the pyrogenic formations were revealed. At the fourth stage, some features appeared that permit us to recognize the development of soddy soils on the pyrogenic substrates (i.e., soddy pyrogenic-mucky, soddy pyrogenic-sandy soils, etc.).     

石灰石成土过程中Zn在土壤中的演化和重新分布

The long-term redistribution of Zn in a naturally Zn-enriched soil during pedogenesis was quantified based on mass balance calculations. According to their fate, parent limestones comprised three Zn pools: bound to calcite and pyritesphalerite grains, bound to phyllosilicates and bound to goethite in the inherited phosphate nodules. Four pedological processes, i.e., carbonate dissolution, two stages of redox processes and eluviation, redistributed Zn during pedogenesis. The carbonate dissolution of limestones released Zn bound to calcite into soil solution. Due to residual enrichment, Zn concentrations in the soil are higher than those in parent limestones. Birnessite, ferrihydrite and goethite dispersed in soil horizon trapped high quantities of Zn during their formation. Afterwards, primary redox conditions induced the release of Zn and Fe into soil solution, and the subsequent individualization of Fe and Mn into Zn-rich concretions. Both processes and subsequent aging of the concretions formed induced significant exportation of Zn through the bottom water table. Secondary redox conditions promoted the weathering of Fe and Mn oxides in cements and concretions. This process caused other losses of Zn through lateral exportation in an upper water table. Concomitantly, eluviation occurred at the top of the solum. The lateral exportation of eluviated minerals through the upper water table limited illuviation. Eluviation was also responsible for Zn loss, but this Zn bound to phyllosilicates was not bioavailable.