Stages Of Pedogenesis Research Articles

Development of soil food web of microbes and nematodes under different agricultural practices during the early stage of pedogenesis of a Mollisol

Agricultural practices such as tillage and organic amendment influence development of the soil food web. However, such effects are not well understood at the initial stage of soil formation. Using an eight-year field experiment established on exposed parent materials of a Mollisol, the objectives of this study were: (1) to determine the effects of agricultural practices on soil food web structure in comparison to the structures of soil nematode guilds and microbial communities, per se; (2) to elucidate the development of the food web of the young soils in relation to parent materials and a mature Mollisol; and (3) to identify the controlling factors of such relationships. The microbial biomass expressed in phospholipid fatty acids and the abundance of nematode guilds increased in the field treatments compared with parent materials by a larger magnitude in Gram positive (G+) bacteria and plant parasite (PP) nematodes under perennials than under cropping. The abundance of bacterivorous (Ba) nematode guilds was significantly correlated with microbial biomass of total bacteria, but not with that of G+ or G− bacteria. The abundance of total Ba, particularly Ba1 nematode guilds was positively correlated with soil organic carbon and its related nutrient contents. Redundancy analysis showed that the structure of food web was similar to nematode guild structure rather than to soil microbial community structure among the soils. The food web structure was separated between the soils under perennials and those under cropping via Axis 1 and between fertilized and not fertilized soils irrespective of land uses via Axis 2. The separations via Axis 1 were mainly driven by PP nematodes in association with high C:N soils, suggesting the determinant effect of land use type, while the separations via Axis 2 were driven by Ba nematodes and bacteria in association with soil physical and chemical properties, indicating the role of soil carbon and nutrients. The food web in the arable soils with more organic amendments was similar to that of mature Mollisol. These findings suggest that soil food web at the early pedogenesis can develop quickly with restoration practices and the development was more affected by land use type than by soil management practices.

Sulfur dynamics during long-term ecosystem development

Long-term soil and ecosystem development involves predictable changes in nitrogen (N) and phosphorus (P) availability and limitation, but far less is known about comparable changes in sulfur (S) despite its importance as an essential plant macronutrient and component of soil organic matter. We used a combination of elemental analysis, X-ray absorption spectroscopy, hydrolytic enzyme assays, and stable S isotope ratios to examine S in soil and leaf tissue along the 120,000-year Franz Josef chronosequence, New Zealand. Total soil S concentrations increased during the early stages of pedogenesis and then declined as soils aged. There was little variation in soil N:S ratios along the chronosequence other than in the youngest (5 year old) soil, although the carbon (C):S ratio increased markedly in the oldest soils and the P:S ratio decreased continuously along the chronosequence. Foliar S concentrations and N:S ratios varied widely among common plant species but did not change consistently with increasing soil age, although foliar P:S declined for several species in the older stages of the chronosequence. The chemical nature of soil organic S extracted from mineral and organic horizons and determined by S K-edge X-ray absorption near-edge fine-structure (XANES) spectroscopy was dominated by C-bonded S distributed approximately equally in highly-reduced and intermediate oxidation states, although ester-bonded S was also abundant throughout the chronosequence. Soil sulfatase activity expressed on a soil C basis was highest in young soils, indicating low S availability in the early stage of pedogenesis. Enzymatic C:S and N:S ratios varied little during ecosystem development, although the enzymatic P:S ratio increased continuously along the chronosequence. Stable S isotope ratios (δ34S) increased along the chronosequence, particularly in the early stages of pedogenesis, reflecting a shift in S inputs from primary mineral S to oceanic sulfate in atmospheric deposition. Overall, this first comprehensive assessment of S along a long-term soil chronosequence suggests that S availability is low in the earliest stage of pedogenesis, but then remains stable throughout the progressive and retrogressive phases of ecosystem development, despite pronounced shifts in the chemistry and dynamics of other nutrients.

Molybdenum sources and isotopic composition during early stages of pedogenesis along a basaltic climate transect

Molybdenum (Mo) is an essential micronutrient and redox sensitive trace metal that has the potential to be a tracer of pedogenic processes. Globally, riverine δ98Mo values (based on 98Mo/95Mo relative to NIST SRM 3134) are heavier relative to bedrock, suggesting weathering processes preferentially retain light Mo isotopes, however, the mechanisms governing this process in soils are poorly understood. We investigated soil Mo abundance and isotopic composition as a function of climate along a well-constrained climosequence on a 10kyr lava flow in Hawaii receiving 660 to 2100mmyear−1 mean annual precipitation (MAP). We assessed Mo abundance and isotopic composition as a function of soil organic matter (OM) content, short-ranged-ordered (SRO) iron (Fe) (oxyhydr)oxide abundance, and Mo loss/gain. We find net accumulation of Mo across all soils (up to +139% gain) that is positively correlated with increasing MAP. The highest Mo gains are in surface soil horizons, and are correlated with high OM content. The isotopic composition of soil Mo, deviates from underlying basaltic bedrock, which ranges from δ98Mo values of −0.11‰ to −0.26‰. Soil Mo isotopic values are lightest at the dry sites (δ98Mo=−0.63‰) and become heavier with increasing precipitation (up to δ98Mo=+0.03‰). Samples with the heaviest δ98Mo values are from horizons with the largest net gains of Mo relative to bedrock and have higher OM content. In order to further constrain Mo fluxes into and out of the soil system, we measured Mo isotope ratios in local rainwater (average δ98Mo=+1.11‰), groundwater (average δ98Mo=+0.14‰), and vegetation (δ98Mo values between −0.18‰ and +0.64‰). Based on these data, we propose that Mo in these soils is substantially augmented by additions from precipitation, volcanic fog, and potentially anthropogenic inputs of Mo, and that retention of these inputs within soils is likely related to Mo–OM interactions. The large atmospheric inputs of Mo strongly modulate the δ98Mo values of dissolved Mo fluxes from soil to values only slightly heavier than bedrock. These patterns illustrate the potential for Mo as a tracer of atmospheric inputs and pedogenic processes in soils and help elucidate the mechanisms that drive heavy δ98Mo values in the global riverine Mo flux.

Инициальное почвообразование в прибрежной Антарктике:существуют ли не орнитогенные почвы?

Tundra soils were formed in a cold environment with harsh winters and short growing season. Most of them are primitive in terms of their profile differentiation and depth. Therefore, studying these soils is important for understanding the initial stages of pedogenesis. Many studies in this field have been carried out in arctic and alpine environments, but there is still some lack of information about Antarctic soils. How­ever, primitive soils of Antarctic tundra and other cold environments may be incomparable because of their different genesis. Impact of ornithogenic products on tundra soils and habitats in Southern Hemisphere is much stronger than in Arctic or alpine environments; but many soils in the coastal Antarctica have no visi­ble signs of ornithogenic influence. In this study we hypothesized that the high content of trace elements in soils may prove their ornithogenic origin. It may be caused by an intensive biogenic flux of chemical ele­ments from marine to terrestrial ecosystems: plankton + microbenthos→N. сопсіппа→L. dominicanus→ guano + pellets (N. сопсіппа shells). In this study we investigated the content of trace elements in soils of Galindez Island and Skua Island (Wilhelm Archipelago). It was found that the content of Ca, Sr and Cd in soils formed on N. сопсіппа shells (ornithogenic soils) was significantly higher than in parent rock. Con­tents of Sr and Cd in soil have strongly correlated with content of Ca, which is the main component of mollusk shells. In some soils formed on rhyolites, the content of these elements in soil was much lower than in parent rock; but linear correlation between Ca and Sr (R2=0.997, p<0.001) as well as between Ca and Cd (R2=0.963, p<0.001) contents was as strong as in soils formed on N. сопсіппа shells. These results support the idea of ornithogenic origin of Ca, Sr and Cd in the Antarctic soils. A further study with a focus on the isotopic composition of these elements is therefore suggested.

Characterization of products of the early stages of pedogenesis in ornithogenic soil from Maritime Antarctica

SummaryLimited pedogenesis on the Antarctic continent results in unusual, but important, short‐range order inorganic phases and organo‐mineral complexes (both with broad peaks from X‐ray diffraction) in the clay fraction, which can be studied by sequential chemical extractions. We aimed to develop a better sequential extraction procedure to obtain more detailed discrimination of the short‐range order phases (SROP) of the clay fraction of soil from Maritime Antarctica. Selected chemical properties of the soil and clay fraction were related to different phases of these products. The total amount of SROP and organo‐mineral complexes in the clay fraction ranged from 15.1 to 43.9%, with greater occurrence in ornithogenic soil. The continuous incorporation of guano from penguins into the soil profile has contributed to increasing amounts of organo‐mineral complexes. Short‐range order phases have an important effect on soil chemical properties, such as an increase in non‐exchangeable acidity, quantity of hydroxyl groups on the surface of the colloidal fraction, the buffering capacity of Al3+ from non‐exchangeable and structural forms of the element, and a decrease in soil CEC. The greater number of sequential extraction steps enabled the separation of SROP and organo‐mineral complexes into two phases of stability, with a clear predominance of the more soluble forms.

Rapid loss of phosphorus during early pedogenesis along a glacier retreat choronosequence, Gongga Mountain (SW China).

The loss of phosphorus (P) during the early pedogenesis stage is important at the ecosystem level, and it also plays an important role in the global P cycle. The seasonal variation of total P (Pt) and its fractions along a young soil chronosequence (Hailuogou chronosequence) on the eastern slope of Gongga Mountain, SW China, was investigated based on the modified Hedley fractionation technique to understand P loss during the early pedogenesis stage. The results showed that the mineral P (mainly apatite) was the dominant fraction of Pt in the C horizon of the soil, and the seasonal difference in Pt and its fractions was insignificant. In the A horizon, Pt concentrations decreased markedly compared with those in the C horizon, and as the age of the soil increased, the inorganic P (Pi) significantly decreased and the organic P (Po) prominently increased. Seasonally, the P fractions exhibited various distributions in the A horizon. The variation of Pt and its fractions revealed that the P loss was rapid along the 120-year soil chronosequence. The P stocks in soils (0–30 cm) started to decrease at the 52 year site. And the P stock depletion reached almost 17.6% at the 120-year site. The loss of P from the soil of the Hailuogou chronosequence was mainly attributed to weathering, plant uptake, and transport by runoff. About 36% P loss was transported into plant biomass P at the 120 year site. The data obtained indicated that the glacier retreat chronosequence could be used to elucidate the fast rate of P loss during the early pedogenic stage.

Oxygen isotopes of phosphate and soil phosphorus cycling across a 6500 year chronosequence under lowland temperate rainforest

Phosphorus (P) availability declines during ecosystem development due in part to chemical transformations of P in the soil. Here we report changes in soil P pools and the oxygen isotopic signature of inorganic phosphate (δ18Op) in these pools over a 6500-year soil coastal dune chronosequence in a temperate humid environment. Total P declined from 384 to 129mgPkg−1 during the first few hundred years of pedogenesis, due mainly to the depletion of primary mineral P in the HCl-extractable pool. The δ18Op of HCl-extractable inorganic P initially reflected the signature of the parent material, but shifted over time towards (but not reaching) isotopic equilibrium. In contrast, δ18Op signatures of inorganic P extracted in water and NaHCO3 (approximately 9 and 39mgPkg−1, respectively) were variable but consistent with isotopic equilibrium with soil water. In the NaOH-extractable P pool, which doubled from 63 to 128mgPkg−1 in the early stages of pedogenesis and then gradually declined, the δ18Op of the extracted inorganic P changed from equilibrium values early in the chronosequence to more depleted signatures in older soils, indicating greater rates of hydrolysis of labile organic P compounds such as DNA and increase involvement in P cycling as overall P availability declines through the sequence. In summary, this application of δ18Op to a long-term soil chronosequence provides novel insight into P dynamics, indicating the importance of efficient recycling through tight uptake and mineralization in maintaining a stable bioavailable P pool during long-term ecosystem development.

A plant-root system in the Lower Devonian of the Holy Cross Mountains, Poland

The depositional environment of the Lower Devonian of the Holy Cross Mountains has only been studied and interpreted in part, particularly for the lower portion of the profile. Recent fieldwork findings suggest a considerable change with regard to earlier hypotheses. Apart from the sedimentological observations that indicate marginal marine and very shallow-water conditions, horizons with plant-root traces and layers interpreted as palaeosols showing different stages of pedogenesis have been documented. The presence of palaeosols in some areas of the Holy Cross Mountains is the first direct evidence for the existence of terrestrial conditions during the Lower Devonian in this area. This plant-root system is one of the oldest fossil records ever described globally.

Modern and relict features in clayey cryogenic coils: Morphological and micromorphological identification .

The research was performed in the south-eastern part of Russia. Soils were formed on clayey parent materials under an extreme continental climate favorable for the deep freezing and maintenance of permafrost. Based on morphological, micromorphological, physical and chemical attributes, the soils represent a soil complex that includes Vertic Luvic Phaeozems (Clayic and Turbic) and Luvic Phaeozems (Clayic and Turbic). Decomposition, aggregation, eluviation, illuviation, pedoturbation, mineralization and hardening result from accumulation and transformation of organic matter, freeze-thaw, shrink-swell, and translocation processes, and cryoturbation. The soil complex is interpreted as polygenetic. Interpretations were made in order to differentiate modern soil processes from relict ones. The most ancient features correspond to the cold Pleistocene glacial period and include cryogenic wedges, permafrost involutions, disrupted soil horizons, cryogenic sorting of coarse material, and accumulation of the organic matter above the permafrost. A subsequent stage of pedogenesis under a warmer and wetter environment is reflected by black humus crack infillings, black humus aggregates deep in the subsoil, vertical translocation of mobile organic matter, and the formation of clay coatings. Finally, the current climate is a warmer but more arid pedoenvironment. It is recorded in the soil complex by brownish fulvic humus and the formation of vertic features. Even in this last relatively warm climatic stage, vertic features formed by shrinking and swelling processes co-exist with annual deep freezing of the soils and subsoil permafrost at a depth of about ~300 cm.

Organic carbon accumulation on soil mineral surfaces in paddy soils derived from tidal wetlands

We studied organic carbon (OC) accumulation in organo-mineral associations during soil development on calcareous parent material. Two chronosequences in the Zhejiang Province, PR China, were investigated; one under paddy cultivation with a maximum soil age of 2000years, and the other under upland crops where the oldest soil was 700years old. Bulk soils and soil fractions of the uppermost A horizons were analyzed for OC concentrations, radiocarbon (14C) contents, total pedogenic iron oxide concentration and oxalate extractable proportions of iron (FeOX) oxides. The specific surface area of soil minerals was measured with the Brunauer–Emmett–Teller (BET-N2) method on four conditions: untreated, after organic matter removal, after iron oxide removal and after removal of both. Initial soil formation on calcareous marine sediments includes soil decalcification and OC accumulation. Paddy soils are characterized by an accelerated decalcification, higher contents of OC and FeOX oxides, and a pronounced accumulation of modern OC. The mineral constitution of the soil material indicated already a certain degree of weathering since the earliest stages of pedogenesis and remained unchanged in paddy and non-paddy soils. The study provides no evidence of formation of new clay-sized minerals during soil development, which could supply new surfaces for OC accumulation. However, the study revealed higher OC coverage on mineral surfaces in decalcified paddy soils. Therefore, we assume the specific surface area and the specific affinity of FeOX oxides for OC storage to play an important role for OC accumulation in organo-mineral associations. In contrast, the surface area of minerals in non-paddy soils, in which decalcification and the proportion of FeOX oxides were much lower, showed significantly lower OC coverage. Selective removal of SOM or iron oxides clearly showed that iron oxides and SOM protect each other in organo-mineral associations primarily in paddy fine clay-sized fraction. Thus, we explained the higher OC coverage on mineral surfaces by complex association between clay minerals, iron oxides and SOM in paddy soils.

Image analysis of soil thin sections for a non-destructive quantification of aggregation in the early stages of pedogenesis

SummaryOne major challenge facing soil micromorphology is the direct quantification of aggregation. This study proposes a generic protocol to quantify aggregation properties directly in undisturbed soil samples by image analysis of soil thin sections. We worked on a constructed Technosol proposed as an experimental model with controlled characteristics. Two sampling campaigns were conducted in 2008 and 2010 on an in situ plot, where 24 undisturbed soil samples were collected each year. Thin sections were prepared, scanned to generate images and processed using the protocol developed. Aggregates from 50 to 2000 µm equivalent diameters were monitored. Six aggregate properties were quantified: number, area, perimeter, eccentricity, shape and equivalent diameter. A synthetic mean index of aggregation (MIAia) was calculated from image analysis. We confirmed that aggregation is closely related to porosity, as highlighted by the MIAia. Three aggregate properties: number, area and shape were selected as the indicators most representative of aggregation evolution during the early stages of pedogenesis. In further developments, direct (image analysis) and indirect (stability tests) methods for the quantification of aggregation could be proposed as complementary ways of describing and quantifying total quantities of stable macroaggregates in soils.RésuméL'un des défis de la micromorphologie en sciences du sol est de pouvoir quantifier globalement et de manière directe l'agrégation. Cette étude propose un protocole générique de quantification directe des paramètres d'agrégation par analyse d'images de lames minces d'échantillons de sols non perturbés. Nous avons travaillé sur un Technosol construit proposé comme un modèle expérimental présentant des caractéristiques connues. Deux campagnes d'échantillonnage ont été conduites en 2008 et 2010 sur une parcelle expérimentale in situ, au cours desquelles 24 échantillons non perturbés de Technosols ont été collectés chaque année. Des lames minces ont été réalisées, scannées et les images obtenues ont été analysées à l'aide du protocole spécifiquement développé. Les agrégats de diamètres compris entre 50 et 2000 µm ont été suivis au cours du temps. Pour cela six paramètres ont été quantifiés : nombre, surface, périmètre, excentricité, forme et diamètre équivalent. Un indice synthétique : Indice Moyen d'Agrégation en analyse d'image (IMAai) a été calculé. Nous avons confirmé que l'agrégation est étroitement corrélée à la porosité, cette relation étant plus marquée en utilisant l'IMAai. Trois paramètres descriptifs des agrégats sont sélectionnés comme indicateurs de l'évolution de l'agrégation dans les stades précoces de la pédogenèse. Des perspectives de développement résident dans l'utilisation complémentaire de méthodes directes (analyse d'images) et indirectes (tests de stabilité) de quantification de l'agrégation pour décrire et quantifier l'ensemble des macroagrégats et leur fraction stable dans les sols.

Early transformation and transfer processes in a Technosol developing on iron industry deposits

SummaryLarge surface areas covered with man‐made materials are subject to pedogenetic evolution. However, pedogenetic processes in the resulting Technosols are seldom fully assessed. This work was conducted to identify and characterize the processes occurring on deposits of industrial technogenic materials. A former settling pond of the iron and steel industry where a forest has established since termination of the industrial activity approximately 50 years ago was chosen. A 2‐m deep pit was opened, and a series of layers of the soil profile were sampled. The macro‐ and micro‐structure were studied, and soil samples were analysed for structural, chemical and mineralogical assessment (chemical analyses, X‐ray diffraction, infrared and Mössbauer spectroscopies, scanning and transmission electron microscopies coupled with energy dispersion spectrometry). Results showed that the profile was composed of a succession of sub‐horizontal layers arranged in two groups according to their structure and composition, linked to the composition of the industrial effluent. Group 1 was composed of iron‐, carbonate‐ and aluminosilicate‐rich layers exhibiting a compact structure. Group 2 contained manganese‐rich layers with a friable structure. Pedogenetic processes of various intensities were detected at different depths. Besides an accumulation of organic matter at the surface, transformations of minerals were recorded all along the soil profile, with weathering, leaching and precipitation of new phases. Phenomena occurred primarily in specific zones, such as cracks and interfaces between two layers. In conclusion, the soil maintained characteristics of the original industrial material and displayed several stages of pedogenesis, which were controlled chronologically by climatic and biological factors.

Early stages of pedogenesis at the bottom of a 30-year-old artificial depression under semidesert conditions

Initial soils that developed at the bottom of an artificial hollow 30 × 40 m in size and 3 m in depth have been studied. The hollow was dug on a plot with a predominance of solonetzic complexes in the soil cover on the territory of the Dzhanybek Research Station in 1979. A soil with a shallow but clearly differentiated profile composed of a litter, a humus-accumulative W horizon leached from carbonates, and an underlying C1ca horizon with a high content of dispersed carbonates formed in the hollow over 30 years. The total thickness of these horizons is 7–10 cm. The morphology of the profile corresponds to the slightly alkaline humus-accumulative calcareous soil type of the order of immature soils in the current classification of Russian soils. The soil-sediment layer to a depth of >80 cm contains little soluble salts, predominantly sulfates; the content of exchangeable Na does not exceed 1 meq/100 g. Groundwater of calcium sulfate composition occurs at a depth of ∼3.8 m. These features, together with additional moistening by low-saline melt water, ensure favorable conditions for the spontaneous propagation and development of herbaceous, shrubby, and woody plants in the bottoms of artificial hollows. The development of a soil profile is accompanied by the depletion of the clay fraction from the upper W horizon, presumably due to the predominant removal of smectite minerals. In the upper W horizon, transformations of layered aluminosilicates takes place: it involves the formation of illites from smectites and from smectitic layers in illite-smectite mixed-layered minerals and partial vermiculitization of chlorites. The technology used upon the excavation of the hollow can be recommended for growing woody-shrubby plants on soils of the solonetzic complex in the clay semidesert during a relatively short time period.

Biogeochemical cycling of soil phosphorus during natural revegetation of Pinus sylvestris on disused sand quarries in Northwestern Russia

Quarrying causes severe degradation of soils and vegetation that can be recovered partially when the quarries are abandoned and re-colonised by plants. To understand the recovery of soil functionality and nutrient cycling, we studied the development of soil phosphorus pools during Scots pine (Pinus sylvestris) revegetation in a disused sand quarry in Northwestern Russia. Sites that had been developing for different times since abandonment were compared to the parent sand and an adjacent undisturbed forest. Phosphorus speciation in genetic horizons of soil profiles was determined by sequential fractionation and solution phosphorus-31 nuclear magnetic resonance spectroscopy. Rapid transformations in soil properties occurred in 40 years, with a marked decline in pH and an accumulation of organic matter. Phosphorus transformations were shaped by geochemical processes, with a rapid release of inorganic phosphorus from primary minerals and accumulation of organic phosphorus to concentrations exceeding those found in the undisturbed site. Adsorbed and/or precipitated phosphorus increased rapidly, despite few reactive mineral colloidal surfaces. Natural succession of Scots pine in post-mining landscapes promotes ecosystem restoration through the rapid re-establishment of the biogeochemical cycles of organic matter and phosphorus. This study provides an important example of biogeochemical phosphorus cycling during the initial stages of pedogenesis.

Soil sulphur speciation in two glacier forefield soil chronosequences assessed by SK‐edge XANES spectroscopy

SummaryIn regions with little atmospheric input of sulphur (S) and S‐poor parent material, the bio‐availability of S, which is dependent on its speciation, may limit ecosystem production and succession. In our study, soil S speciation in two glacier forefield soil chronosequences (Hailuogou Glacier, Gongga Shan, China; Damma Glacier, Swiss Alps) was investigated for the first time. Different S species were quantified by synchrotron‐based X‐ray absorption near‐edge structure (XANES) spectroscopy at the S K‐edge. Both chronosequences show similar patterns and pedogenetic trends of their topsoil S status. Topsoil concentrations of total S were correlated with the concentrations of organic carbon and pedogenic Fe/Al oxyhydroxides. Both moraine materials contained inorganic sulphides, which in the topsoil were oxidized within 30 (Hailuogou) or 75 years (Damma) of soil development after deglaciation. About 50% of total S in the fresh moraine material at Hailuogou and 75% of that in the 15 year‐old soil at Damma was organically‐bound. During initial soil development, the contribution of organic S to total S increased at the expense of inorganic sulphide and sulphate, resulting in organic S percentages > 90% of total topsoil S after 30 (Hailuogou) and 75 (Damma) years of pedogenesis. Organic S compounds with electronic oxidation states of the S atom > + 1.5 (sulphoxides, sulphones, sulphonates and ester sulphates) dominated the organic S pool in all soils. Hence, microbial degradation of non‐sulphide organic S (sulphonates and ester sulphates) is probably important to mitigate S scarcity caused by limited availability of SO42−‐S in these soils. Changes in topsoil S speciation during initial stages of pedogenesis and ecosystem succession in glacier forefields under a cool, humid climate appear to be governed by combined effects of mineral weathering (oxidation of inorganic sulphides and formation of S‐adsorbing sesquioxides), accumulation and microbial turnover of soil organic matter and the type of vegetation succession.

Synchrotron-based P K-edge XANES spectroscopy reveals rapid changes of phosphorus speciation in the topsoil of two glacier foreland chronosequences

Phosphorus (P) is a crucial element for life on Earth, and the bioavailability of P in terrestrial ecosystems, which is dependent on the soil P stock and its speciation, may limit ecosystem productivity and succession. In our study, for the first time a direct speciation of soil P in two glacier foreland chronosequences has been conducted using synchrotron-based X-ray Absorption Near-Edge Structure (XANES) spectroscopy. The chronosequences are located in the forefields of Hailuogou Glacier (Gongga Shan, China) and Damma Glacier (Swiss Alps). The age since deglaciation of the investigated soils ranges from 0 to 120years at Hailuogou, and from 15 to >700years at Damma. Differences in climate conditions (cooler at Damma, in contrast to Hailuogou precluding the establishment of forest in advanced ecosystem succession stages) and in the chemical composition of the parent material result in different soil contents of total P and Fe/Al oxyhydroxides, which are much smaller at Damma than at Hailuogou. Nevertheless, both chronosequences show similar trends of their topsoil P status with increasing soil age. Our study reveals a rapid change of topsoil P speciation in glacier retreat areas already during initial stages of pedogenesis: Initially dominating bedrock-derived apatite-P and Al-bound P is depleted; Fe-bound P and particularly organically-bound P is accumulated. Organic P strongly dominates in the topsoil of the mature soils outside the proglacial area of Damma Glacier (age 700–3000years), and already 50years after deglacation in the topsoil of the retreat area of Hailuogou Glacier. A key factor for the change in topsoil P speciation is the establishment of vegetation, resulting in soil organic matter (SOM) accumulation as well as accelerated soil acidification and apatite dissolution by organic acids, which are produced by SOM-degrading micro-organisms, mykorrhiza fungi, and plant roots. Particularly the succession of grassland to forest seems to accelerate the transformation of topsoil P from apatite-P into organic P. The conceptual model developed by Walker and Syers (1976) to explain long-term (millennial) changes of P speciation, availability, and turnover in soils and terrestrial ecosystems seems to be valid to describe short-term changes of P speciation and P availability in proglacial topsoils already within a century of initial soil formation. Because the apatite-depleted topsoil horizons in the young proglacial soils are shallow, the change of topsoil P speciation should not seriously affect P availability and the P acquisition strategy of adult trees, whose roots can easily access apatite-containing C horizons. In contrast, P acquisition strategies of fungi, micro-organisms and plants confined to the topsoil probably change from apatite dissolution to mineralization of organic P already within <3000years in a proglacial ecosystem succession from bare soil to grassland (Damma Glacier Chronosequence) or even within <100years in a proglacial ecosystem succession to forest (Hailuogou Glacier Chronosequence).

Late Quaternary pedogenesis in periglacial zone of northeastern Europe near ice margins since MIS 3: Timing, processes, and linkages to landscape evolution

Two paleosol-sedimentary sequences Koskovo and Puzbol developed within the nearest periglacial zone of Valday glaciation of the East European Plain (56.7°–58.5° N, the Upper Volga River basin) were studied to reconstruct soil mantle and landscape evolution since Marine Isotope Stage (MIS) 3. The sequences are formed on terraces at 130–141 and 172m a.s.l., constituted by ancient (Early Valday (Würm) or Late Moscow (RissII)) lake clayey sediments. The buried paleosols are represented by system of horizons Hb–G3b (Histosol), Agb–G3b and AGb horizon (Umbric Gleysol). The 14C age of the paleosol humus and peat varied between 50,300–39,700 cal. BP. These paleosols were developed under forest-tundra and pine-spruce forests with the meadow plant communities and the areas of swampy vegetation according to palynological data from Puzbol. They represent the northernmost occurrence of the MIS3 fossil soil in Europe dominated by the features of gleyzation, cryogenic aggregation, cracking, and humus and peat formation. Clay coatings in the Middle Valday paleosols and pedosediments are products of Holocene pedogenesis.The upper lithological layers covering the MIS3 paleosols are loess-like (mantle) loams underlain by clayey Late Pleistocene lake deposits. They mark the presence of wide extraglacial lakes with existed within the Upper Volga basin during the maximum advance of the Valday glaciation (MIS2). Based on the stratigraphy of the studied sections, the highstands of these Late Quaternary lakes might exceed ≈170m a.s.l.For the first time it was possible to date the age of humus-clay coatings developed in the Bthk3 horizon (c.1.6–2.0m) of Puzbol where in the upper part of the section the Cutanic Albeluvisol formed. The Early Middle Holocene age of humic acid of humus-clay coatings (≈10,900 cal. BP) and carbonate nodules 7500–8180 cal. BP refer to the first stage of pedogenesis of this polygenetic soil, which occurred from pre-Boreal to the Atlantic period, and was characterized by dark humus accumulation and carbonate precipitation in a poorly drained landscape. The 14C age of the fulvic acids of these coatings (≈6130 cal. BP) is indicative of the beginning of the second stage, dominated by clay illuviation under a better drained, leaching environment.

Effect of weathering on abundance and release of potentially toxic elements in soils developed on Lower Cambrian black shales, P. R. China

This paper examines the geochemical features of 8 soil profiles developed on metalliferous black shales distributed in the central parts of the South China black shale horizon. The concentrations of 21 trace elements and 8 major elements were determined using ICP-MS and XRF, respectively, and weathering intensity (W) was calculated according to a new technique recently proposed in the literature. The data showed that the black shale soils inherited a heterogeneous geochemical character from their parent materials. A partial least square regression model and EF(bedrock) (enrichment factor normalized to underlying bedrock) indicated that W was not a major control in the redistribution of trace metals. Barium, Sn, Cu, V, and U tended to be leached in the upper soil horizons and trapped by Al and Fe oxides, whereas Sb, Cd, and Mo with negative EF values across the whole profiles may have been leached out during the first stage of pedogenesis (mainly weathering of black shale). Compared with the Chinese average soils, the soils were strongly enriched in the potentially toxic metals Mo, Cd, Sb, Sn, U, V, Cu, and Ba, among which the 5 first listed were enriched to the highest degrees. Elevated concentrations of these toxic metals can have a long-term negative effect on human health, in particular, the soils in mining areas dominated by strongly acidic conditions. As a whole, the black shale soils have much in common with acid sulfate soils. Therefore, black shale soils together with acid sulfate soils deserve more attention in the context of metal exposure and human health.

Behavior of major and trace elements during weathering of sericite–quartz schist

Two regolith profiles developed on the sericite–quartz schist in subtropical humid environment were selected to investigate behaviors of major and trace elements during weathering in Mengman gold deposit of Yunnan province, China. One profile located in the mining district sheared by a fault and the other was outside the mining area which represented the normal weathering profile on the schist. Regolith samples were collected in both profiles sequentially. Thirteen major oxides and 23 trace elements (including REE) were analyzed and their behaviors were compared in these two profiles. Based on the idea that immobile element is just a relative notion, we presented a method of immobile plateau to determine immobile elements during each stage in a progressive geochemical process and used mass ratio ( MR) to calculate the percentage of gain or loss ( X gp ) of each element during the whole process. In both profiles, only TiO 2 was immobile during the whole weathering. The regolith profile formed on the mineralized schist recorded the weathering process more sensitively than the regolith profile on the normal schist. REE was mobile and fractionated during the schist weathering. LREE was loss in mass during the soil development stage which resulted from the chemical leaching, but was gain in mass during the pedogenesis stage because of the preferential absorption of soil to LREE. The LREE depletion near the fault during weathering was the collective effects of chemical leaching and physical accumulation. HFSE were all mobile in the mineralized regolith profile especially near the fault. But Nb–Ta and Zr–Hf were covariant in both profiles during the schist weathering.

Behavior of REE Fractionation during Weathering of Dolomite Regolith Profile in Southwest China

Abstract:REE fractionation during the weathering of dolomite has been recognized for decades. A regolith profile on dolomite in southwest Yunnan of China was selected to investigate the behaviors of REE during weathering. The weathering of dolomite is divided into two stages: the pedogenesis stage and soil evolution stage, corresponding to the saprolites and soils respectively in the regolith profile. SiO2, TiO2, P2O5, Zr, Hf, Nb and Ta were immobile components during the weathering by and large, while Al2O3, K2O and Fe2O3 were lost during the soil evolution stage in the physical form (clay minerals probably). REE were fractionated during the whole weathering of dolomite. The field weathering profile and the lab acid‐leaching experiments on dolomite indicate that MREE were enriched clearly relative to other REE during the pedogenesis stage in a “capillary ascending‐adsorption” mechanism, but they did not fractionate clearly in the soil evolution stage. REE were lost and accumulated in the weathering front of dolomite during the soil evolution stage in a “physical‐chemical leaching” mechanism.