Initial Stages Of Soil Development Research Articles

Changes of soil organic matter stock in meadow ecosystems in the south of Western Siberia

The study was conducted on the Baraba plain in the southern part of Western Siberia. Soil samples in meadow ecosystems that are at different stages of succession after drying of the lake bottom were analyzed. The conducted research allowed us to establish that the content of soil organic matter and microbial biomass (the active part of soil organic matter) in successional ecosystems formed in the floodplain of the drying salt lake gradually increases and in the last stages of development reaches the values of zonal chernozem soils. The process of accumulation of carbon stocks of humus and microbial biomass slows down against the background of a high concentration of salts in individual horizons of young soil profiles. This may be the reason for the revealed pattern, according to which the main carbon stock of humus and microbial biomass are concentrated in the upper (0-10 cm) layer of the emerging soils. This is especially noticeable at the very first initial stage of soil development and the next stage of the salicornia community (Salicornia perennans). In the last stages of succession, solonetz and chernozem-meadow soils are formed under meadow ecosystems. The carbon stock of humus and microbial biomass at these stages of soil development significantly increase against the background of active processes of reducing the amount of salts in the profiles of meadow soils. And only at these last stages there is a significant increase in carbon stocks of humus and microbial biomass in a layer of 10-20 cm.

Microbial Community Structure and Metabolic Potential at the Initial Stage of Soil Development of the Glacial Forefields in Svalbard.

Microbial communities have been identified as the primary inhabitants of Arctic forefields. However, the metabolic potential of microbial communities in these newly exposed soils remains underexplored due to limited access. Here, we sampled the very edge of the glacial forefield in Svalbard and performed the 16S rRNA genes and metagenomic analysis to illustrate the ecosystem characteristics. Burkholderiales and Micrococcales were the dominant bacterial groups at the initial stage of soil development of glacial forefields. 214 metagenome-assembled genomes were recovered from glacier forefield microbiome datasets, including only 2 belonging to archaea. Analysis of these metagenome-assembled genomes revealed that 41% of assembled genomes had the genetic potential to use nitrate and nitrite as electron acceptors. Metabolic pathway reconstruction for these microbes suggested versatility for sulfide and thiosulfate oxidation, H2 and CO utilization, and CO2 fixation. Our results indicate the importance of anaerobic processes in elemental cycling in the glacial forefields. Besides, a range of genes related to adaption to low temperature and other stresses were detected, which revealed the presence of diverse mechanisms of adaption to the extreme environment of Svalbard. This research provides ecological insight into the initial stage of the soil developed during the retreating of glaciers.

Carbon Sequestration Related to Soil Physical and Chemical Properties in the High Arctic

AbstractArctic soils are an important reservoir of soil organic carbon (SOC) and their role in determining arctic ecosystem functioning in global carbon budgets requires closer attention. We investigated the coupling of soil properties and SOC stabilization mechanisms in high Arctic terrestrial habitats differing in vegetation cover and organic matter input. We focused on soil physical and chemical properties in glacier foreland, soil crust, dry tundra, wet tundra, and bird cliff meadow habitats on Svalbard (Norway). Concurrently, we performed physical fractionation to determine the amount of SOC stabilized by mineral associations or occlusion in macro and microaggregates. Initial stages of soil development (glacier foreland and soil crust habitats) exhibited characteristically high bulk density and pH, and low moisture and nutrient contents, whereas more developed soils (dry and wet tundra habitats) showed opposite trends. Contrastingly, bird cliff meadow showed low bulk density, intermediate moisture, and very high nutrient content. The amount of SOC stabilized by mineral associations and occlusion in aggregates generally increased with vegetation cover; hence, the more developed habitats supported higher contents of stabilized SOC. However, SOC was stabilized in aggregates even in initial stages of soil development. SOC content in most fractions correlated positively with contents of dissolved organic carbon and nitrogen, suggesting that both dissolved organic carbon and nitrogen might have provided some degree of SOC stabilization through increased formation of aggregates and suppression of microbial mineralization of soil organic matter, respectively. Our findings underscore the notion that models of SOC sequestration in the Arctic should account not only for total SOC content, but also SOC stabilization mechanisms, as represented by SOC content in respective soil fractions.

Magnetic properties of black cotton soils and lateritic soils developed on the Late Cretaceous Deccan flood basalts of northern Karnataka, India

The magnetic properties of black cotton and lateritic soils developed on Deccan basalts in northern Karnataka, India, have been studied to determine magnetic mineral sources and decipher their relative age. These soils are highly magnetic, indicating lithogenic contribution. The results show that black cotton soils are characterized by coarse-grained stable single-domain (SSD) lithogenic magnetic minerals, and in lateritic soils, it is superparamagnetic (SP) pedogenic magnetic minerals. The main magnetic minerals in black cotton soils are titano-magnetite/maghemite, while in lateritic soils, it is magnetite/maghemite and/or hematite/goethite. The variability of these soils’ magnetic properties is due to changes in the concentration of magnetic minerals, the size of their magnetic grains, or magnetic mineralogy. Black cotton soils are younger and are at the initial stage of soil development, while laterite soils are older and are at the latter stage of soil development.

Napier Grass: A Model Crop for Developing Partially Weathered Gravelly Land in the Central Deccan Plateau Region

The gravel content in the landscape varies in time and space for the interaction of external factors namely climate and vegetation. The vegetation plays a greater role on gravel disintegration in the landscape at initial stage of soil development can be studied keeping other factors as constant. The objective of this study was to account the change of particle content, particle movements, regolith depth, bulk density, soil organic carbon, cation exchange capacity, pH, mineralizable nitrogen and quantification of both above and below ground biomass production of grasses/fodder crops on the gravelly land. In this regard, locally suitable fodder crops such as napier grass, stylo grass, marvel-stylo grass intercrop and marvel grass were raised. Representative soil samples (45–50 kg) were collected from the surface as well as subsurface layers and separated into different sizes for four consecutive years i.e. 2012–13, 2013–14, 2014–15 and 2015–16. The amount of gravel disintegration decreased with increase in gravel size, time and depth. Overall, the gravel reduction under napier grass, stylo-marvel inter cropping system, stylo and marvel grass cultivation were 91, 65, 52 and 21 g kg−1, respectively higher than that of native fallow land. The increase of soil content, regolith depth, soil organic carbon content and mineralizable nitrogen were highly associated with lowering of gravel content, bulk density and soil pH observed across the treatments. To conclude, cultivation of napier grass may be preferred in barren land for faster disintegration of gravels as well as more fodder production and benefit for the subsequent crops to be taken.

Development of microbial community during primary succession in areas degraded by mining activities

AbstractTogether with plants, soil microbial communities play an essential role in the development of stable ecosystems on degraded lands, such as postmining spoil heaps. Our study addressed concurrent development of the vegetation and soil fungal and bacterial communities in the course of primary succession in a brown coal mine spoil deposit area in the Czech Republic across a chronosequence spanning 54 years. During succession, the plant communities changed from sparse plants over grassland and shrubland into a forest, becoming substantially more diverse with time. Microbial biomass increased until the 21st year of ecosystem development and later decreased. Although there was a close association between fungi and vegetation, with fungi mirroring the differences in plant community assemblages, the development of the bacterial community was different. The early succession community in the barren nonvegetated soil largely differed from that in the older sites, especially in its high abundance of autotrophic and free‐living N2‐fixing bacteria. Later in succession, bacterial community changes were minor and reflected the chemical parameters of the soil, including pH, which also showed a minor change with time. Our results show that complex forest ecosystems developed over 54 years on the originally barren soil of the temperate zone and indicate an important role of bacteria in the initial stage of soil development. Although the arrival of vegetation affects substantially fungal as well as bacterial communities, it is mainly fungi that respond to the ongoing development of vegetation.

Rapid changes in phosphorus species in soils developed on reclaimed tidal flat sediments

Phosphorus (P) plays a key role in the global biogeochemical cycle. The dynamics of P in soils is of considerable importance to the management of soil fertility. However, little is known about P dynamics in reclaimed land at the centennial scale during the initial stage of soil development, when the ambient conditions undergo substantial changes. In this study, conducted in Eastern China, we used a sequential extraction method to analyze the changes in P species in sediments and soils in a coastal reclaimed area representing a sequence of soil ages. Significant accumulation of total P accompanied by organic matter enrichment, desalination, and decalcification were observed in the initial pedogenesis of reclaimed tidal flat sediments. A rapid change in top soil P species within a century of pedogenesis was revealed, which was characterized by a marked decline in P contained within primary minerals (DeP) and an increase in loosely absorbed P, Fe-bound P, authigenic P (CaP), and organic P. DeP decreased from 67.3% to 25.3% of total P, whereas CaP increased from 8.4% to 32.9% along the reclamation gradient. Dissolution of primary minerals and a high rate of fertilization were identified as the major causes of this P trajectory. A key factor controlling the evolution of soil P speciation is the marked change in ambient conditions following land conversion, resulting in a shift in anaerobic conditions, a decrease in pH, accumulation of organic matter, and depletion of carbonates. Under the strong interference of human activities, the P dynamics in soils derived from tidal flat sediments differ from those predicted by the Walker and Syers model. Our results indicate that current nutrient management practices in the studied area can not only avert soil P depletion but also increase P availability.

Changes in small organic N during early stages of soil development

During the early stages of ecosystem development there are increases in plant and soil microbial biomass, nutrient availability and rates of nutrient cycling; but little is known about how pools of small organic N vary during the initial stages of soil development. The aim of this study was to examine how the pool of small organic N compounds varies during the initial stages of soil development, and if age differentially affects D- and L-enantiomers of protein amino acids. Measurements were made at a soil chronosequence on the east coast of Tasmania that comprised a series of sub-parallel beach dunes and ridges varying in age from <100 years to 5500 years. Capillary electrophoresis-mass spectrometry was used to identify and quantify the main small organic N compounds in free, adsorbed and microbial fractions of the soil; while chiral liquid chromatography-mass spectrometry was used to quantify amino acid enantiomers in hydrolysed soil and the free, adsorbed and microbial fractions of soil.CE-MS detected 66 small (<250 Da) organic N compounds of which 63 could be positively identified. Small organic N was dominated by protein amino acids, while there were also large amounts of quaternary ammonium compounds and alkylamines. There were differences among chronosequence sites in the profile of small organic N, but these differences were not monotonically related to age and there was no evidence for a build-up of recalcitrant compounds over time. Differences were instead site-specific and related to presence/absence of particular non-protein amino acids which probably related to the presence/absence of specific plants and/or microbes that produce and/or can metabolise different non-protein amino acids.In free solution and microbial biomass D enantiomers of many amino acids were below detection limits (i.e. < 0.125 nmol g−1) and D-enantiomers were at low concentrations relative to L enantiomers such that across all ages and replicates the summed concentration of d-amino acids was 0-3-0.6% of L amino acids. There was no evidence that absolute or relative concentrations of D-enantiomers in free solution, microbial biomass or hydrolysates were larger at the older chronosequence sites. The consistent lack of an effect of soil age on D/L probably indicates that the turnover of soil proteins is comparatively rapid and thus soil proteins are similarly young even among sites in which soil age is vastly different.

Fungi contribute more than bacteria to soil organic matter through necromass accumulation under different agricultural practices during the early pedogenesis of a Mollisol

Living and dead microbial organisms contribute to the sequestration of soil organic carbon (SOC). The contributions of different community compositions are not well understood, particularly at the initial stage of soil development. Using an eight-year field experiment established on exposed parent material (PM) of a Mollisol, our objectives were (1) to differentiate microbial biomass and necromass of different microbial communities, and (2) to elucidate their contributions to SOC under different agricultural practices compared to PM and an arable Mollisol without C amendment (MO). The field treatments included two no-tilled soils supporting perennial plants (Alfalfa, and natural fallow), and four tilled soils under rotation between maize and soybean in alternate years, with or without chemical fertilization and crop residue amendment. Bacterial and fungal derived necromass were estimated by comparing amino sugars (ASs) contained in living and dead cell walls and phospholipid fatty acids (PLFAs) contained in living cell membranes, assuming that the conversion factor between cell membrane and wall for all microbes was one. The ratio of living microbial biomass estimated in ASs to that as indicated by total PLFAs was 0.76–0.87, indicating a high reliability of the estimation. Microbial biomass parameters in the field treatments were lower than those in MO and higher than those in PM. Both PLFAs and ASs demonstrated that bacteria dominated over fungi (70.2% v.s. 12.6%), but the fungal derived necromass were larger than bacterial derived necromass (70.7% v.s. 25.9%) in the studied soils. The microbial contribution to SOC was larger in necromass than in living biomass. The contribution of fungal derived necromass to SOC was dominant in soils and showed the same order among the soils as the fungal biomass, i.e. being larger under alfalfa than under natural fallow and in the tilled soils with organic C amendment than those without organic C input. These results suggested that only shift in fungal community due to land use change and organic C input could influence microbial contribution to soil organic carbon stabilization.

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.

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.

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.

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.

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.

Influence of landslides on biophysical diversity — A perspective from British Columbia

Landslides have long been overlooked or underestimated as important natural disturbance agents. In particular the ecological role of landslides in maintaining biological diversity has been largely ignored. Here we provide a western Canadian ( British Columbian) perspective on the influences of landslides on biophysical diversity, which is related in several ways to biological diversity. We recognize several types of biophysical/ecological diversity: site diversity, soil diversity, and the derivative habitat or ecosystem (including aquatic ecosystems) diversity. There are also a variety of landslide types, depending on materials and on the rate and style of movement. We discuss the roles of different landslide types on various aspects of terrestrial diversity. Landslides are simultaneously depositional and erosional processes that influence sites by redistributing materials and changing surface expression — usually creating a complex microtopography that can include very dry ridges and hummocks, and sometimes depressions with standing water. Landslide impacts to site also influence soil and soil development. Portions of landslides with exposed parent material are set back to the initial stages of soil development and ecological succession. Landslides can also change soil density, structure, porosity, surface texture, chemistry and microclimate. By changing site and soil, landslides also influence habitat. Landslides influence habitat diversity by engendering a mosaic of seral stages (often both primary and secondary), and in overwhelmingly forested landscapes often create nodes or hotspots of non-forested habitat and biota. In some areas, like the boreal forest, there is an important interplay between landslides and fire, while on the coast of British Columbia debris and snow avalanches can be the dominant disturbance agent. Low-gradient and deep-seated landslides are often opportunistically colonized by beaver and other water and shrub-loving fauna. Sag ponds and impounded streams provide aquatic habitat — often with standing dead trees. Landslide rubble and scarps provide denning/nesting habitat, escape terrain, and cliff habitat for vertebrates.

Microbial Properties of Mine Spoil Materials in the Initial Stages of Soil Development

The early years of soil genesis during mine spoil reclamation are critical for vegetative establishment and may help predict reclamation success. Mine spoils in the Halle‐Leipzig region of Germany were analyzed for microbial changes following a hay mulch‐seeding treatment without topsoil or fertilizer application. Microbial biomass carbon (Cmic) and dehydrogenase activity (DHA) of spoils were measured each year in the first 3 yr after treatment. In the third year, bacterial community DNA fingerprints were compared with those from a reference soil. Microbial indicators were measured at three depths in the upper 10 cm of spoils at three sites with contrasting parent materials: glacial till (sandy loam), limnic tertiary sediments (high‐lignite sandy clay loam), and quaternary sand and gravel (loamy sand). Before reclamation, Cmic means and standard deviations of surface spoils (0–1 cm) were 9 ± 6, 39 ± 11, and 38 ± 16 mg kg−1 for the loamy sand, high‐lignite sandy clay loam, and sandy loam spoils, respectively. Within one year, mean Cmic at the surface increased to 148 ± 70, 229 ± 64, and 497 ± 167 mg kg−1, respectively, and was significantly higher at 0 to 1 cm than at lower depths. Highest DHA and DNA yields were obtained in the 0‐ to 1‐cm depth of the sandy loam spoils. Microbial biomass C values exhibited significant correlations with DHA, DNA yield, and extractable C for all three mine spoils. Soil microbial indices were more responsive than plant measurements to differences in parent materials.

EVALUATION OF THE ARYA-PARIS MODEL FOR ESTIMATING WATER RETENTION CHARACTERISTICS OF LIGNITIC MINE SOILS

Mine soil materials may be viewed as man-made systems that consist of spatially disordered soil and sediment components, which are in an initial stage of soil development. A question is whether methods and approaches developed for natural soils may also be used for such artificially created soil materials. The applicability of the Arya and Paris pedotransfer function to obtain hydraulic properties from the particle size distribution and bulk density was tested for lignitic mine soil material of the Lusatian Lignite Mining District in eastern Germany. The scaling factor α in this model was evaluated by (i) fitting of the water retention curves estimated with the Arya-Paris model (APM) to measured water retention data and (ii) interpretation of α as a fractal dimension of the pore channels and derivation of this fractal dimension from the fractal dimension of the particle size distribution. The two tested fractal approaches resulted in relatively inaccurate predictions of the water content. The use of a single fitted α value for each depth yielded α values between 1.05 and 1.47. Because of the inability of the APM to account for residual water contents in this sandy soil material, a correction was applied. The cumulative mass fraction fractal method did not improve the estimation in comparison with the retention curves calculated with a constant α value of 1.38. The closest fits with the data were obtained by using a variable α value that depended on the particle size. The accuracy of the predictions of the APM in the higher suction range could be improved (lower mean deviations and root mean square deviations of water content) by using a linear water content-dependent correction factor. Better estimates of water retention in the relatively dry range may be significant for simulation of water budgets of mine spoil sites in the Lusatian Mining District.

Stand composition affects soil quality in oak stands on reclaimed and natural sites

In many afforested reclamation sites as well as in commercial forests naturally settled shrubs or trees (“non-target species”; NTS) are cut down to improve the growth of the target trees (TT). In afforested oak plantations ( Quercus robur) of the Rhineland (Germany) the NTS broom ( Cytisus scoparius) and birch ( Betula pendula) can occur in high densities during the first decades of succession. Hazel ( Corylus avellana) is a common shrub in the understory of commercial oak forests ( Quercus petraea). We studied the influence of these NTS on selected physical, chemical and biotic soil properties in cultures of oak (TT). Soil samples taken under single oak trees were compared with samples taken under broom and birch at afforested reclamation sites of different age (2, 9, 13 years) and with samples taken under hazel in an 80-year-old oak forest. At initial stages of succession (2 years) all of the investigated soil properties indicated a higher soil quality under broom than under oak. However, the advantage of broom was less evident in a later stage of succession (9 years). Birch (13 years) and hazel (80 years) only improved soil chemical properties. The soil pH and the content of Mg 2+ were significantly higher under birch, the contents of Ca 2+, Mg 2+ and PO 4 3− were significantly higher under hazel than under oak ( p=0.05). The results demonstrate that the selected NTS improve soil quality in afforested and commercial oak forests. This effect is pronounced under the influence of broom at initial stages of soil development.

Effects of climate and landscape development on the terrestrial phosphorus cycle

Past variations in the terrestrial cycle of phosphorus (P), a biolimiting nutrient, are poorly understood. Detailed geochemical analysis of P in lake-sediment cores spanning the late Pleistocene to the present from the western Appalachian Plateau, the Coast Mountains of British Columbia, and the San Bernardino Mountains of southern California reveal large changes in terrestrial P cycling. P is transformed from a mineralized form to more bioavailable forms with increased soil development and landscape stability in the catchments. This process occurs relatively rapidly (i.e., within 3,000--5,000 yr) and can be reset quickly; the degree of transformation depends on local climate and the starting point of the soil system. The release of solid-phase P from these landscapes follows modeled patterns of high rates during the initial stages of soil development and low rates upon soil and landscape stabilization. Changes in weathering style were confirmed for the southern California catchment by analysis of Ge/Si ratios of lake diatoms, which revealed substantially higher values during an interval of high P release and low values at present. These records point to significant variability in the terrestrial P mass balance on glacial time scales, a feature that needs to be incorporated into models of nutrient andmore » carbon cycling in the past.« less