Stages Of Soil Development Research Articles

Vertical distribution of the soil microbiota along a successional gradient in a glacier forefield.

Spatial patterns of microbial communities have been extensively surveyed in well-developed soils, but few studies investigated the vertical distribution of micro-organisms in newly developed soils after glacier retreat. We used 454-pyrosequencing to assess whether bacterial and fungal community structures differed between stages of soil development (SSD) characterized by an increasing vegetation cover from barren (vegetation cover: 0%/age: 10 years), sparsely vegetated (13%/60 years), transient (60%/80 years) to vegetated (95%/110 years) and depths (surface, 5 and 20 cm) along the Damma glacier forefield (Switzerland). The SSD significantly influenced the bacterial and fungal communities. Based on indicator species analyses, metabolically versatile bacteria (e.g. Geobacter) and psychrophilic yeasts (e.g. Mrakia) characterized the barren soils. Vegetated soils with higher C, N and root biomass consisted of bacteria able to degrade complex organic compounds (e.g. Candidatus Solibacter), lignocellulolytic Ascomycota (e.g. Geoglossum) and ectomycorrhizal Basidiomycota (e.g. Laccaria). Soil depth only influenced bacterial and fungal communities in barren and sparsely vegetated soils. These changes were partly due to more silt and higher soil moisture in the surface. In both soil ages, the surface was characterized by OTUs affiliated to Phormidium and Sphingobacteriales. In lower depths, however, bacterial and fungal communities differed between SSD. Lower depths of sparsely vegetated soils consisted of OTUs affiliated to Acidobacteria and Geoglossum, whereas depths of barren soils were characterized by OTUs related to Gemmatimonadetes. Overall, plant establishment drives the soil microbiota along the successional gradient but does not influence the vertical distribution of microbiota in recently deglaciated soils.

Short-term effects of plant litter addition on mineral surface characteristics of young sandy soils

Initial stages of soil development are characterized by structural changes of mineral surfaces over time. The specific surface area (SSA) is closely related to pedogenic properties and soil organic matter (SOM). Interactions between SOM and mineral surfaces induce quantitative and qualitative changes in SSA and corresponding soil properties. However, the knowledge about ranges, effects and mechanisms of organic coverage in the very initial phase of pedogenesis is very limited. Therefore, our objective was to study these processes in young sandy soils and the effects of plant litter addition. Soil samples taken from the constructed catchment “Chicken Creek” were used in a microcosm experiment over 80weeks. The silt and clay fractions of samples (<63μm) were analyzed before the experiment and after 40 and 80weeks. The effects of litter addition and weathering on SSA were assessed using the BET-N2 sorption approach. We found increases of SSA between 16.4% and 41.6% within the 80week experimental period, but a relative reduction in SSA due to organic coverage of these new surfaces after plant litter addition. The removal of the soil organic matter (SOM) by muffling increased SSA (6.8–12.9%). The results for SSA corresponded to changes in surface specific parameters like cation exchange capacity (CEC), surface enthalpy and the fractional coverage of mineral surfaces by SOM. In conclusion, the results showed that the soils were clearly in a very initial state of soil development. However, the potential of these young sandy soils to adsorb nutrients and soil organic matter as one of the main important soil functions clearly increased within the relatively short experimental period and changes in SSA indicate relatively large increases in mineral surfaces within short time periods during the initial phase of soil development compared to long-term pedogenesis.

Apatite Loss in Pothwar Loess Plain (Pakistan) Fits a Simple Linear Reservoir Model

Apatite is the dominant phosphorus (P) mineral in early stages of soil development, and its redistribution as labile forms under pedogenesis controls terrestrial bioavailability. Quantitative distribution of labile forms of P and apatite-P was examined in Pothwar Loess Plain, Pakistan where the degree of pedogenesis varied with relief. Four soil types, Typic Ustorthents (Rajar), Typic Calciustepts (Missa), Udic Calciustepts (Basal), and Udic Haplustalfs (Guliana), were sampled from three replicated locations at genetic horizon level. With the exception of total P value at surface, the mean total and apatite-P decreased towards the surface in Udic Haplustalfs and Udic Calciustepts where dicalcium and octacalcium phosphate increased toward surface. Iron (oxides and oxyhydroxides) adsorbed and occluded P forms were also in greater quantities in Udic Haplustalfs and increased toward the surface, whereas they were lowest and uniform in the Typic Ustorthents. Aluminum- and organic P correlated with soil organic matter. Apatite-P decreased exponentially with an increase in the sum of iron adsorbed and occluded P fractions, and fitted the equation M(x) = M0[1 – exp(–wx)] with r2 = 0.996, where M(x) is the mean apatite-P concentration in solum, M0 is the apatite-P content in the loess sediments, x is the cumulative iron adsorbed and occluded P, and w is an empirical factor indicating the change rate of apatite-P in the loess. From the calculated apatite-P of 740 mg kg−1 at the time of deposition, mean apatite-P loss was 60% in Udic Haplustalfs, 33% in Udic Calciustepts, 23% in Typic Calciustepts, and 8% in Typic Ustorthents. The transformation of soil P to labile forms was faster and deeper in level or slight depressions followed by gently sloping areas in wide plains, and was the least in the gullied land.

Nutrient addition dramatically accelerates microbial community succession.

The ecological mechanisms driving community succession are widely debated, particularly for microorganisms. While successional soil microbial communities are known to undergo predictable changes in structure concomitant with shifts in a variety of edaphic properties, the causal mechanisms underlying these patterns are poorly understood. Thus, to specifically isolate how nutrients – important drivers of plant succession – affect soil microbial succession, we established a full factorial nitrogen (N) and phosphorus (P) fertilization plot experiment in recently deglaciated (∼3 years since exposure), unvegetated soils of the Puca Glacier forefield in Southeastern Peru. We evaluated soil properties and examined bacterial community composition in plots before and one year after fertilization. Fertilized soils were then compared to samples from three reference successional transects representing advancing stages of soil development ranging from 5 years to 85 years since exposure. We found that a single application of +NP fertilizer caused the soil bacterial community structure of the three-year old soils to most resemble the 85-year old soils after one year. Despite differences in a variety of soil edaphic properties between fertilizer plots and late successional soils, bacterial community composition of +NP plots converged with late successional communities. Thus, our work suggests a mechanism for microbial succession whereby changes in resource availability drive shifts in community composition, supporting a role for nutrient colimitation in primary succession. These results suggest that nutrients alone, independent of other edaphic factors that change with succession, act as an important control over soil microbial community development, greatly accelerating the rate of succession.

Effect of plant litter addition on element leaching in young sandy soils

AbstractThe knowledge about element leaching and biogeochemical cycles during initial stages of soil development is very limited. Therefore, we studied the effects of parent material characteristics and plant litter addition on element leaching from young sandy soils in a microcosm experiment. Our objective was to evaluate the function of young soils as a source and/or sink for nutrients during initial pedogenesis and to identify main processes which are involved in the initial development of biogeochemical cycles. The main research questions were: (1) How do differences in parent material characteristics affect nutrient leaching?; and (2) How is nutrient leaching of young soils influenced by litter addition of different plant functional groups (e.g., legume and grass species)? Combined treatments of two minimally weathered parent materials (pure sand and loamy sand) with plant litter of two plant species (Lotus corniculatus L. and Calamagrostis epigejos L.) were investigated in a soil column experiment. In addition, control columns with parent material or plant litter only were included. Carbonate weathering as a main source for calcium leaching was induced by the moderately acidic irrigation solution used in the experiment. It was 7.5 fold greater for the loamy sand parent material compared to the pure sand despite lower carbonate contents in the loamy sand. Leaching of K was very low for both parent materials but greater for the loamy sand parent material, likely due to transfer processes from fixed to exchangeable potassium forms in the clay minerals of the loamy sand. Plant litter addition generally increased leaching losses. Carbonate dissolution was intensified by both plant litter types, especially by L. corniculatus, very likely due to H+ released during nitrification of N released from plant litter and an increase in partial pressure of CO2 from microbial respiration. In contrast, K was largely retained in the soils, probably due to fixation by clay minerals and microbial immobilization. Only the pure sand treated with L. corniculatus litter leached K, resulting in 4–6 fold greater leaching losses compared to all other treatments. Nitrogen released from L. corniculatus litter was almost completely nitrified and was nearly doubled as compared to that from C. epigejos, resulting in greater N leaching. The results of our study allow identifying the general function and processes of vegetation patches in young ecosystems formed as a result of initial parent material characteristics and invading vegetation with respect to litter decomposition, soil solution composition, nutrient retention and leaching, and effects on the soil mineral phase. These patterns are not mere additive effects of parent materials plus plant litter, but reflect differences in biogeochemical process intensities and could result in an increasing heterogeneity of soil properties, nutrient availability, and element leaching fluxes with time.

Dynamics of bacterial community succession in a salt marsh chronosequence: evidences for temporal niche partitioning.

The mechanisms underlying community assembly and promoting temporal succession are often overlooked in microbial ecology. Here, we studied an undisturbed salt marsh chronosequence, spanning over a century of ecosystem development, to understand bacterial succession in soil. We used 16S rRNA gene-based quantitative PCR to determine bacterial abundance and multitag 454 pyrosequencing for community composition and diversity analyses. Despite 10-fold lower 16S rRNA gene abundances, the initial stages of soil development held higher phylogenetic diversities than the soil at late succession. Temporal variations in phylogenetic β-diversity were greater at initial stages of soil development, possibly as a result of the great dynamism imposed by the daily influence of the tide, promoting high immigration rates. Allogenic succession of bacterial communities was mostly driven by shifts in the soil physical structure, as well as variations in pH and salinity, which collectively explained 84.5% of the variation concerning community assemblage. The community assembly data for each successional stage were integrated into a network co-occurrence analysis, revealing higher complexity at initial stages, coinciding with great dynamism in turnover and environmental variability. Contrary to a spatial niche-based perspective of bacterial community assembly, we suggest temporal niche partitioning as the dominant mechanism of assembly (promoting more phylotype co-occurrence) in the initial stages of succession, where continuous environmental change results in the existence of multiple niches over short periods of time.

Early stages of soil development on serpentinite: the proglacial area of the Verra Grande Glacier, Western Italian Alps

PurposeClimate change is driving strong variations in mountain habitats, such as glacier retreat, which is releasing large surfaces soon colonized by vegetation and attacked by weathering and pedogenesis. Many proglacial soil chronosequences have been studied in different parts of the world, but no study is available on early soil development and pedogenesis on serpentinite.Materials and methodsWe analysed the development of the main chemical (pH, organic matter, nutrients and exchangeable cations) and morphological properties in three soil chronosequences in the Verra Grande Glacier forefield (Italian side of the Monte Rosa Group, Western Alps), characterized by slightly different parent materials (pure serpentinite or serpentinite with small gneiss inclusions) and topography (steep lateral moraines or flat basal till).Results and discussionOrganic matter accumulation, acidification and base and metal leaching are the most important pedogenetic processes active during early stages of soil formation on serpentinite in the upper subalpine altitudinal belt. These processes are associated with minor changes in color and structure showing weak mineral weathering. Biocycling of nutrients is limited on pure serpentinite because of weak primary productivity of the plant community. Pedogenesis is quite slow throughout the forefield, and it is slowest on pure serpentinite. On flat surfaces, where slow erosion permits a fast colonization by Ericaceae, the podzolization process begins after few centuries since moraine deposition, while on steep slopes more time is required.ConclusionsPedogenesis on serpentinite is extremely slow. The fast colonization by grassland species increases the speed of pedogenetic trends where serpentinitic till is enriched by small quantities of P-rich gneiss. The encroachment of forest-shrub species increases the speed of pedogenetic trends thanks to a strong nutrient biocycling.

Nutrient Biogeochemistry During the Early Stages of Delta Development in the Mississippi River Deltaic Plain

Nutrient biogeochemistry associated with the early stages of soil development in deltaic floodplains has not been well defined. Such a model should follow classic patterns of soil nutrient pools described for alluvial ecosystems that are dominated by mineral matter high in phosphorus and low in carbon and nitrogen. A contrast with classic models of soil development is the anthropogenically enriched high nitrate conditions due to agricultural fertilization in upstream watersheds. Here we determine if short-term patterns of soil chemistry and dissolved inorganic nutrient fluxes along the emerging Wax Lake delta (WLD) chronosequence are consistent with conceptual models of long-term nutrient availability described for other ecosystems. We add a low nitrate treatment more typical of historic delta development to evaluate the role of nitrate enrichment in determining the net dinitrogen (N2) flux. Throughout the 35-year chronosequence, soil nitrogen and organic matter content significantly increased by an order of magnitude, whereas phosphorus exhibited a less pronounced increase. Under ambient nitrate concentrations (>60 μM), mean net N2 fluxes (157.5 μmol N m−2 h−1) indicated greater rates of gross denitrification than gross nitrogen fixation; however, under low nitrate concentrations (<2 μM), soils switched from net denitrification to net nitrogen fixation (−74.5 μmol N m−2 h−1). As soils in the WLD aged, the subsequent increase in organic matter stimulated net N2, oxygen, nitrate, and nitrite fluxes producing greater fluxes in more mature soils. In conclusion, soil nitrogen and carbon accumulation along an emerging delta chronosequence largely coincide with classic patterns of soil development described for alluvial floodplains, and substrate age together with ambient nitrogen availability can be used to predict net N2 fluxes during early delta evolution.

The role of microorganisms at different stages of ecosystem development for soil formation

Abstract. Soil formation is the result of a complex network of biological as well as chemical and physical processes. The role of soil microbes is of high interest, since they are responsible for most biological transformations and drive the development of stable and labile pools of carbon (C), nitrogen (N) and other nutrients, which facilitate the subsequent establishment of plant communities. Forefields of receding glaciers provide unique chronosequences of different soil development stages and are ideal ecosystems to study the interaction of bacteria, fungi and archaea with their abiotic environment. In this review we give insights into the role of microbes for soil development. The results presented are based on studies performed within the Collaborative Research Program DFG SFB/TRR 38 (http://www.tu-cottbus.de/ecosystem ) and are supplemented by data from other studies. The review focusses on the microbiology of major steps of soil formation. Special attention is given to the development of nutrient cycles on the formation of biological soil crusts (BSCs) and on the establishment of plant–microbe interactions.

A quantitative model for integrating landscape evolution and soil formation

AbstractLandscape evolution is closely related to soil formation. Quantitative modeling of the dynamics of soils and landscapes should therefore be integrated. This paper presents a model, named Model for Integrated Landscape Evolution and Soil Development (MILESD), which describes the interaction between pedogenetic and geomorphic processes. This mechanistic model includes the most significant soil formation processes, ranging from weathering to clay translocation, and combines these with the lateral redistribution of soil particles through erosion and deposition. The model is spatially explicit and simulates the vertical variation in soil horizon depth as well as basic soil properties such as texture and organic matter content. In addition, sediment export and its properties are recorded. This model is applied to a 6.25 km2 area in the Werrikimbe National Park, Australia, simulating soil development over a period of 60,000 years. Comparison with field observations shows how the model accurately predicts trends in total soil thickness along a catena. Soil texture and bulk density are predicted reasonably well, with errors of the order of 10%, however, field observations show a much higher organic carbon content than predicted. At the landscape scale, different scenarios with varying erosion intensity result only in small changes of landscape‐averaged soil thickness, while the response of the total organic carbon stored in the system is higher. Rates of sediment export show a highly nonlinear response to soil development stage and the presence of a threshold, corresponding to the depletion of the soil reservoir, beyond which sediment export drops significantly.

Morphology of physical soil crusts and infiltration patterns in an artificial catchment

Hydraulic properties of the soil surface control the partitioning of rainfall between infiltration and runoff. For agricultural soils in humid climate regions, physical soil crusts have mostly been reported to reduce water infiltration. For initial soils developing in such climate on unstructured sediments without organic carbon, effects of soil crusting and slaking on infiltration was largely unknown. The objective was to compare initial soil and porous system formation with infiltration from three locations in a constructed hydrological catchment that has been left to undirected ecological succession for three years. We expected to find characteristic, mainly textural, effects of physical soil crusts during this initial stage of soil development. The three-dimensional (3D) micro-morphology was described using the X-ray computed tomography (CT); two-dimensional (2D) infiltration patterns were obtained from drip infiltration experiments using time-resolved neutron radiography (NT). Selected samples from three locations represent major sediment types of the catchment. The CT data indicated structural crusts on soil consisting of sandy to loamy sediments and depositional crusts on more sandy sediments. A combination of these two types developed at locations with silt to fine sand sediments; probably as a result of aeolian deposition on a structural crust. Moreover, isolated vesicle-shaped pores mostly reported from soils in arid environments were observed in most samples. The 2D infiltration patterns reflected the structural alteration by crusts only in samples containing silt and fine sand. Infiltrating water tended to pond within the aeolian deposits above the underlying structural crust. For all other samples, 2D infiltration pattern were relatively uniform; only negligibly small effect of structural crusts and vesicular pores on infiltration and redistribution could be observed in NR experiments although field measured infiltration rates were different. The relatively small differences in moisture patterns observed using NT suggest that the texture-related differences in physical soil crusts indicated by pore structure images using CT had only little effects on infiltration. The study improved understanding soil structure and water distribution relations in a hydrological catchment during initial ecosystem development.

Changes of soil phosphorus speciation along a 120-year soil chronosequence in the Hailuogou Glacier retreat area (Gongga Mountain, SW China)

The Hailuogou Glacier (Gongga Mountain, SW China) has been retreating in response to global warming. A soil chronosequence (Hailuogou Chronosequence) has developed in the retreat area, and a primary plant succession has developed on it. To investigate the changes of soil phosphorus (P) fractions along the young soil chronosequence in the cold and humid climate, soil samples were collected at seven sites of different ages (0 to 120years). In all soil samples, concentrations of total P and of different P fractions (Bioavailable P, Al/Fe-bound P (P bound by Al and Fe oxides or hydroxides), Ca-bound P, and residual P) were determined using a sequential extraction technique. Organic P was determined using the high temperature ignition method. For the youngest (0years, 12years) soils, P forms were dominated by residual P, and topsoil forms of Ca-bound P, Al/Fe-bound P, organic P, microbial biomass P and bioavailable P were less than 1.86%. From 30 to 120years, for the topsoil, concentrations of Ca-bound P and organic P gradually increased; the concentration of bioavailable P in surface soil also showed a trend of increase, with percentages of 5–11.5% to total soil P; the concentration of residual P decreased; the concentration of Fe/Al-bound P contributed less than 5% to total soil P at all sites. Ca-bound P and organic P were the dominant P fractions at the older sites (ages: 80 and 120years). Soil P bioavailability and solubility were influenced by the changes of pH, and concentrations of Fe and Al oxide and hydroxide. The variations of vegetation and microbial activity are also considered as the impact factors of soil P forms. In the later stage of soil development (80~120years), plenty of soil P was transformed into biomass P pool (299.3kgha−1).

Biogeochemical changes during early development of restored calcareous wetland soils

Preservation and restoration of wetlands is critical to maintain their key functional roles of improving water quality, carbon sequestration, and mitigation of greenhouse gas emissions. Restoration of former agricultural wetlands often requires severe measures including removal nutrient-enriched soil followed by natural succession involving changes in nutrient storages and transformations. The focus of this study was to assess changes in biogeochemical parameters during the early stages of soil development following complete soil removal in a calcareous subtropical wetland. Results indicated that significant changes occur in the first 16years including increased soil depth, accumulation of organic matter, carbon (C), nitrogen (N), and phosphorus (P). Early development of soils showed a shift from initial N limitation towards a state of co-limitation by N and P after 16years. Functional responses of these changes were determined by monitoring the microbe-driven processes (enzyme activities and soil oxygen demand) with respect to the nutrient changes. Soil β-glucosidase activity increased in the first few years and then declined with age of the soils. Alkaline phosphatase activity was inversely correlated to the P concentration in soils. When compared with an undisturbed reference site, these parameters indicate that N processes recover more rapidly than those of P and C, but functional attributes related to P limitation should begin to mimic restored conditions within the next century.

Microbial cell-envelope fragments and the formation of soil organic matter: a case study from a glacier forefield

Genesis of soil organic matter (SOM) during pedogenesis is still a matter of controversy in soil science. Recently, it was hypothesized that microbial cell-envelope fragments contribute significantly to SOM formation. We tested the relevance of this process during pedogenesis by evaluating the development of SOM along a chronosequence of a glacier forefield (Damma glacier). Samples of increasing soil age collected along the forefield were analyzed for C and N contents, phospholipid and total fatty acids (PLFA and tFA), water contact angle, micro-hydrophobicity and surface coverage by microbial cell-envelope residues. The surface coverage was visualized and quantified by analysis of representative, equally-scaled scanning electron micrographs (SEM). Increasing SOM contents were accompanied by increasing coverage and overall abundance of microbial cell-envelope fragments as evaluated on the basis of scanning electron microscopy; this is also reflected in the amounts of tFA and PLFA, the trend of C/N ratios, and the increasing hydrophobicity and water contact angles of the soil samples. Using SEM and the image analysis approach, we can provide a process-based description of the development of SOM in the newly developing ecosystem of the glacier forefield. The majority of small-sized SOM visible with scanning electron microscopy appears to consist of bacterial cell envelope fragments that remain stable after cell death, such that their shape does not change with soil age. Our results show the importance of microbial processing of SOM, and highlight the existence of microbial necromass as a significant part of the fine-particulate SOM even in later stages of soil development.

Bacterial communities in soil mimic patterns of vegetative succession and ecosystem climax but are resilient to change between seasons

Organism succession during ecosystem development has been researched for aboveground plant communities, however, the associated patterns of change in below-ground microbial communities are less described. In 2008, a study was initiated along a developmental sand-dune soil chronosequence bordering northern Lake Michigan near Wilderness Park (WP). It was hypothesized that soil bacterial communities would follow a pattern of change that is associated with soil, plant, and ecosystem development. This study included 5 replicate sites along 9 soils (n = 45) ranging in age from ∼105 to 4010 years since deposition. Soil bacterial community composition and diversity were studied using bacterial tag-encoded FLX amplicon pyrosequencing of the 16S rRNA gene. Bray–Curtis ordination indicated that bacterial community assembly changed along the developmental soil and plant gradient. The changes were not affected by seasonal differences, despite likely differences in plant root C (e.g. exudates), temperature, and water availability in soil. Soil base cations (Ca, Mg) and pH declined, showing log-linear correlations with soil age (r ∼ 0.83, 0.84 and 0.81; P < 0.01). Bacterial diversity (Simpson's 1/D) declined rapidly during the initial stages of soil development (∼105–450 y) and thereafter (>450 y) did not change. Turnover of plant taxa was also more rapid early during ecosystem development and correlated with bacterial community structural change (P < 0.000001; r = 0.56). It is hypothesized that plants help to drive pedogenic change during early (<450 y) soil development (e.g. pH decline, cation leaching) which drive selection of soil bacterial communities. In mature soils (∼450–4000 y), resilient and stable soil bacterial community structures developed, mimicking steady-state climax communities that were observed during latter stages of primary plant succession. These relationships point to possible feedbacks between plant and bacterial communities during ecosystem development.

Eco-environmental spatial characteristics of Fildes Peninsula based on TuPu models

This study applies a TuPu analysis to investigate ecological and environmental aspects of an Antarctic ice-free area,using Fildes Peninsula as an example. The TuPu unit was determined using a vector-grid mixed data model. Information from theeco-environment elements was effectively extracted, and was generalized into different classes by means of data mining technology.A series of single-factor thematic information TuPu models, such as topography, soil, animal and vegetation, and human activitiesfor Fildes Peninsula were built in this study. The topography TuPu model contained information on elevation and slope.The soil TuPu model involved soil development stages and soil thickness information. The animal and vegetation TuPu modelcontained the distribution of animals, plant types, lichen cover and lichen height. The human activities TuPu model included populationdensity and human disturbance index information. The landscape comprehensive information TuPu model of Fildes Peninsulaalso was established, and contains twenty-nine landscape units and twelve types of combined environments. The study quantitativelyrevealed the spatial morphology and correlation of the regional eco-environment based on the analysis of these TuPumodels. From these models, we can draw the conclusion that there is a regular differentiation of eco-environment from the coastalbands to the central hills in Fildes Peninsula, and that the eco-environment condition of the eastern coasts is different from that ofthe western coasts. The eco-environmental spatial variation also differs greatly from north to south. Based on analysis of spatialcorrelation, the vegetation in Fildes Peninsula has the greatest correlation with human activity, and has a certain correlation withtopography and soil. This research may provide a new technical approach and scientific basis for the in-depth study of Antarcticeco-environments.

Landscape evolution and changes in soil hydraulic properties at the decadal, centennial and millennial scale: A case study from the Campine area, northern Belgium

Soil hydraulic properties evolve over time as a result of soil formation processes. We investigated the rate and circumstances of change in soil hydraulic properties as a result of soil and landscape evolution that took place over a period of a few decades to several thousands of years. To this end, a sediment-soil sequence in which different sandy landscapes and associated soils are preserved was studied with respect to its geomorphological and pedohydrological characteristics. Three stages of soil development corresponding to specific landscapes were observed within a 2-m deep profile: 1) a stabilisation surface within an active drift sand landscape, 2) an A-horizon that developed on a stabilised drift sand landscape and 3) a pronounced podzol that developed in a stabilised landscape from the last glacial. Measurement of soil physical properties was conducted including grain size analysis, organic carbon content, soil water retention characteristic and hydraulic conductivity using constant head and air permeability analyses. Age control of soil horizons and vegetation history were obtained from optically stimulated luminescence (OSL) dating, radiocarbon ( 14 C) dating, pollen analysis and historical archives. The results suggest a strong relationship between landscape evolution, soil development and hydraulic properties. Small changes in hydraulic properties may already be observed on a decadal and centennial scale, while long-term podzolisation processes may decrease the hydraulic conductivity of parent material up to three orders of magnitude in several thousands of years. It is concluded that combination of geomorphological and pedohydrological analyses of sediment-soil archives may provide a unique means to gain insight into the rate and extent of past changes in soil hydraulic properties and the consequences of future hydrological changes as a result of these evolving properties. ► The influence of evolving sandy landscapes on soil hydraulic properties is investigated. ► Landscape reconstruction techniques and pedohydrological methods are used. ► Below and above order of magnitude K sat changes can be observed on various timescales.

Effects of Ground‐Dwelling Beetle Burrows on Infiltration Patterns and Pore Structure of Initial Soil Surfaces

By modifying the soil structure, flora and fauna play a major role in controlling water infiltration and erosion. Little is known, however, about local feedback effects during the initial stage of soil development. Initial soil formation was studied in an artificial catchment where coarse‐textured, sandy sediments were left to undirected succession. In a patchy moss‐covered area, the surface was colonized by larvae of the ground‐dwelling beetle Cylindera arenaria viennensis [Schrank, 1781], as indicated by millimeter‐sized cylindrical burrows. Our objective was to study the effects of both moss vegetation and beetle larvae on pore structure and infiltration. The pore structure of sparsely and densely moss‐vegetated and unvegetated samples containing a single burrow was characterized by x‐ray computed tomography (CT). Flow patterns of infiltration experiments were visualized using neutron radiography (NR). The micro‐CT scans revealed a variety of more unstable pore systems in the bare soil, locally compacted regions in the moss‐covered samples, and isolated vesicular pores similar to those reported for desert soils. The NR series showed water flow around the cylindrical burrow under initially moist conditions and pronounced preferential flow within the burrow under initially dry soil conditions. Water‐repellent regions in the initially dry sample explained pressure buildup before gravity‐driven flow in the burrow started. The moss cover seemed to stabilize the surface soil, visible in the absence of a depositional sediment layer. The results suggest that moss vegetation and ground beetle burrowing activity control initial soil development by modifying pore structure and water infiltration.

Testing a soil development model against southern Norway soil chronosequences

The first results of modeling soil development in marine sediments in S Norway using the model SoilGen are compared to measured properties of two soil chronosequences, on the western and eastern side of Oslofjord, respectively. The aim of this work is to test how well soil development under well-defined environmental conditions can be modeled. Such testing reveals to what degree soil-forming processes are understood, allowing formulation of adequate calculations reflecting these processes.The model predicts particle size distribution reasonably well, although clay depletion in the upper parts of the soils as a result of clay migration is overestimated. The model tends to underestimate contents of organic carbon and CEC in the A horizons: below, modeled CEC matches well with measured CEC. Base saturation is overestimated in the upper 40 cm and underestimated below. Apparently, leaching of bases proceeds less rapidly in reality than is predicted by the model, due to strong soil structure of the B horizons, causing preferential flow and base leaching around the aggregates, whereas bases inside the aggregates are only slightly affected by leaching.Difficulties and possibilities for improvements are identified, some related to model input data and some to the model itself. Input data could be improved by determining the amounts of organic carbon in organic surface horizons and by quantifying effects of bioturbation. A big challenge is the implementation of soil structure formation in the model. Quantitative data on the development of soil structure with time that can be included in a model are required. Amounts, distribution and connectivity of macro pores need to be defined for each stage of soil development, and zones of low and high base leaching need to be distinguished in the model for each time step.The long-term aim of this work is to model soil development with different sets of soil-forming factors, e.g. different climatic conditions in order to reliably predict soil development under different climate scenarios and related sets of soil-forming factors. The results of the first model runs and the identified possible improvements suggest that this aim is generally achievable.

Microbial food web dynamics along a soil chronosequence of a glacier forefield

Abstract. Microbial food webs are critical for efficient nutrient turnover providing the basis for functional and stable ecosystems. However, the successional development of such microbial food webs and their role in "young" ecosystems is unclear. Due to a continuous glacier retreat since the middle of the 19th century, glacier forefields have expanded offering an excellent opportunity to study food web dynamics in soils at different developmental stages. In the present study, litter degradation and the corresponding C fluxes into microbial communities were investigated along the forefield of the Damma glacier (Switzerland). 13C-enriched litter of the pioneering plant Leucanthemopsis alpina (L.) Heywood was incorporated into the soil at sites that have been free from ice for approximately 10, 60, 100 and more than 700 years. The structure and function of microbial communities were identified by 13C analysis of phospholipid fatty acids (PLFA) and phospholipid ether lipids (PLEL). Results showed increasing microbial diversity and biomass, and enhanced proliferation of bacterial groups as ecosystem development progressed. Initially, litter decomposition proceeded faster at the more developed sites, but at the end of the experiment loss of litter mass was similar at all sites, once the more easily-degradable litter fraction was processed. As a result incorporation of 13C into microbial biomass was more evident during the first weeks of litter decomposition. 13C enrichments of both PLEL and PLFA biomarkers following litter incorporation were observed at all sites, suggesting similar microbial foodwebs at all stages of soil development. Nonetheless, the contribution of bacteria, especially actinomycetes to litter turnover became more pronounced as soil age increased in detriment of archaea, fungi and protozoa, more prominent in recently deglaciated terrain.