Chemical characterization and decomposition of organic matter from two contrasting grassland soil profiles

Particle size fractions of soils from the surface 6 cm of two adjacent grassland plots which, as a result of different fertilizer treatments since 1897, have either a mor or a mull humus form were analysed using solid-state ¹³C nuclear magnetic resonance spectroscopy and fractionation of organic N by steam distillation. In the mor humus soil, which had received 180 kg (NH⁴)²SO⁴ ha^?1 annually and was pH 4.3, there was more C and N in the larger particle size fractions than in the mull humus soil (pH 5.8). The NMR spectra of correspondingly sized soil fractions were similar for both soils. The intensities of NMR signals between 0 and 40 ppm (alkyl-C) and between 160 and 200 ppm (carbonyl-C) increased with decreasing particle size. The intensities of the NMR signals between 60 and 90 ppm (0-alkyl-C) and between 90 and 110 ppm (acetal- and ketal-C) decreased with increasing particle size. Comparison of the NMR spectra of the >2000 um fractions from both soils with those of dried grass litter from the same plots indicated the exclusive plant origin of the C in the largest size fraction of the soils. NMR resonances between 40 and 60 ppm were attributed to alkyl-amino-C because their intensities agreed with the amino-N determinations obtained during organic N fractionation. During incubation in soil microcosms, the larger sized fractions decomposed more rapidly than the smaller fractions. However, all the correspondingly sized particle fractions from the two soils decomposed at the same rate except the >2000 pm fractions. The largest size fraction from the mor humus soil decomposed faster than that from the mull humus soil. This difference in decomposition rate could not be attributed to differences in the chemical composition of the >2000 pm fraction.     

Polycyclic Aromatic Hydrocarbons Content in Contaminated Forest Soils with Different Humus Types

The aim of the study was to determine polycyclic aromatic hydrocarbon (PAH) content in different forest humus types. The investigation was carried out in Chrzanów Forest District in southern Poland. Twenty research plots with different humus types (mor and mull) were selected. The samples for analysis were taken after litter horizons removing from a depth of 0–10 cm (from the Of- and Oh-horizon total or A-horizon). pH, organic carbon and total nitrogen content, base cations, acidity, and heavy metal content were determined. In the natural moisture state, the activity of dehydrogenase was determined. The study included the determination of PAH content. The conducted research confirms strong contamination of study soil by PAHs and heavy metals. Our experiment provided evidence that different forest humus types accumulate different PAH amounts. The highest content of PAHs and heavy metals was recorded in mor humus type. The content of PAHs in forest humus horizon depends on the content and quality of soil organic matter. Weaker degradation of hydrocarbons is associated with lower biological activity of soils. The mull humus type showed lower content of PAHs and at the same time the highest biological activity confirmed by high dehydrogenase activity.     

Spatial and temporal variation in podzol organic matter studied by pyrolysis-gas chromatography/mass spectrometry and micromorphology

A well‐developed podzol hydrosequence that has been partially covered with drift sand, and partially subjected to improved drainage, provides new insights into the causes of variation in soil organic matter chemistry in such soils. While E horizons invariably move towards a dominance of aliphatic components reflecting residual accumulation, the chemistry of organic matter in well‐drained B horizons is determined mainly by decaying roots, which are transformed by microorganisms to humus aggregates. In poorly drained, stratified B horizons, humus coatings dominate and the chemistry is very close to that of dissolved organic carbon. When a sand cover inhibits the supply of fresh litter, microbial decomposition in the A horizon causes a shift in chemistry towards that of the E horizon. Similarly, upon improved drainage and removal of complexed metals from the top of the B horizon, microbial decomposition of all palatable organic matter in the top of the B horizon causes a shift towards E‐horizon chemistry. This is probably the mechanism by which most E horizons in podzols are formed, and not by re‐solution. Marked chemical changes upon improved drainage may take only decades. During microbial decay, small polysaccharide‐derived pyrolysis products (mainly furans, furaldehydes and acetic acid) remain abundant due to the contribution of microbial sugars. Both micromorphology and factor analysis on quantified results of pyrolysis‐gas chromatography/mass spectrometry contribute significantly to the interpretation of the humus chemistry of these profiles and thus to our understanding of soil genesis. Organic chemistry of the investigated podzols can be understood only in the context of their genesis.     

Chemistry of soil organic matter as related to C : N in Norway spruce forest (Picea abies(L.) Karst.) floors and mineral soils

Due to high nitrogen deposition in central Europe, the C : N ratio of litter and the forest floor has narrowed in the past. This may cause changes in the chemical composition of the soil organic matter. Here we investigate the composition of organic matter in Oh and A horizons of 15 Norway spruce soils with a wide range of C : N ratios. Samples are analyzed with solid‐state ¹³C nuclear magnetic resonance (NMR) spectroscopy, along with chemolytic analyses of lignin, polysaccharides, and amino acid‐N. The data are investigated for functional relationships between C, N contents and C : N ratios by structural analysis. With increasing N content, the concentration of lignin decreases in the Oh horizons, but increases in the A horizons. A negative effect of N on lignin degradation is observed in the mineral soil, but not in the humus layer. In the A horizons non‐phenolic aromatic C compounds accumulate, especially at low N values. At high N levels, N is preferentially incorporated into the amino acid fraction and only to a smaller extent into the non‐hydrolyzable N fraction. High total N concentrations are associated with a higher relative contribution of organic matter of microbial origin.     

Humus forms and metal pollution in soil

Smelters in northern France are a serious source of soil pollution by heavy metals. We have studied a poplar plantation downwind of an active zinc smelter. Three humus profiles were sampled at increasing distance from the smelter, and the thickness of topsoil horizons was measured along a transect. We analysed the vertical distribution of humus components and plant debris to assess the impact of heavy metal pollution on the humus forms and on soil faunal activity. We compared horizons within a profile, humus profiles between them, and traced the recent history of the site. Near the smelter, poplar trees are stunted or dead and the humus form is a mor, with a well‐developed holorganic OM horizon. Here faunal activity is inhibited, so there is little faecal deposition and humification of plant litter. At the distant site poplar grows well and faunal activity is intense, so there are skeletonized leaves and many organo–mineral earthworm and millipede faecal pellets. The humus form is a mull, with a well‐developed hemorganic A horizon. The passage from mor to mull along the transect was abrupt, mor turning to mull at 250 m from the smelter, though there was a progressive decrease in heavy metal deposition. This indicates that there was a threshold (estimated to be 20 000 mg Zn kg^?1) in the resilience of the soil foodweb.     

A PYROLYSIS-GAS CHROMATOGRAPHY METHOD FOR DISCRIMINATION OF SOIL HUMUS TYPES

Principles governing the choice of a pyrolysis-gas chromatography method for work on soils and organic macromolecules are reviewed, and the method is applied to the discrimination of mull and mor humus in freely drained soils. Relatively undecomposed surface humus shorizons yield pyrolysis products characteristic of lignin, but these are not present in mineral horizons apart from traces persisting in some podzol A horizons. Mor humus incorporated in A horizons is characterized by a high pyrolysate content of furfurals and phenols whilst mull humus yields proportionately more pyrrole. Humus in B horizons yields a low furfural content with respect to pyrrole and a low content of polar heteroatomic molecules with respect to benzene, toluene, and light molecules of low polarity.     

Origin of the nitrogen assimilated by soil fauna living in decomposing beech litter

We investigated the nitrogen source for main taxa of soil fauna in two beech forests of contrasted humus type using ¹⁵N-labelled beech litter and ¹⁵N analysis of soil fauna. ¹⁵N-labelled beech litter was deposited on the topsoil in December 2000 in four stands of different ages at Leinefelde (Germany) with mull humus and in one mature stand at Sorø (Denmark) with moder humus. The fate of the tracer isotope was measured in litter and soil, as well as in the soil fauna, and for each taxa, we calculated the proportion of N in the animal derived from the labelled substrate. Of the original N contained in the litter, 20-41% was lost after 9 months at Leinefelde, and only 10% at Sorø. This loss was counterbalanced by the incorporation of 24-31% external N at Leinefelde, and 31% at Sorø, partly originating from fungal colonisation of the added litter. The proportion of N assimilated from the labelled litter by the different soil animals varied in relation to their mobility and feeding preferences. Large and mobile soil animals, especially predators, derived on average less ¹⁵N because they were also able to feed outside the labelled litter boxes. Detritivores assimilated at most 15% of their nitrogen content at Leinefelde and 11% at Sorø from the decomposing labelled litter. The most labelled taxa at Leinefelde were small fungivorous and coprophagous species, mainly isotomid Collembola such as Isotomiella and Folsomia. At Sorø, best labelled taxa were saprophagous species such as Enchytraeidae, Glomeridae and Phthiracaroidea. These low rates of ¹⁵N assimilation indicate that fresh litter is not directly the main N source for soil animals. The results obtained suggest that soil fauna fed preferentially upon microorganisms colonising the litter at Leinefelde (mull) and from litter itself at Sorø (moder).     

Humus Forms in Forest Soils: Concepts and Classifications

The concepts and classifications of humus forms developed since the time of scientific pedology formation are critically discussed. The concept of humus forms (types) relates to the classification of a set of topsoil organic and organomineral horizons, which reflects morphologically distinct phases of plant litter and soil organic matter decomposition, but not to the fractions of soil organic matter. Humus forms reflect various types of transformation and accumulation of organic matter in the soil. The stages of development and modern classifications of humus forms abroad are described. The taxonomy of humus forms in Russian literature and its application for the mapping and evaluation of forest soils are considered, as well as its use for the mathematical simulation of soil organic matter mineralization and humification. Prospects for the development of the classification of humus forms in combination with the basic soil classification of European Russia are discussed. A call for an understanding and a common language in soil science at the international level is underlined.     

Monitoring of the humus status of soils of the Ingulets irrigation system

The results of long-term studies (1957–2007) of the changes in the morphology of soil profiles and in the reserves and fractional composition of the humus in the soils of the Ingulets irrigation system are discussed. After 50 years of irrigation, the boundaries of the genetic horizons shifted downward by 15–30 cm. The redistribution of the humus took place: its content decreased to a low level in the plow layer of the irrigated and rainfed soils and significantly increased in the layer of 60–100 cm so that the reserves of humus in the layer of 0–100 cm somewhat increased and corresponded to a moderate level. The distribution of humus in the soil profiles was characterized by the gradual lowering down the soil profile. The concentration of nitrogen in the humus of the irrigated southern chernozems was very low. The degree of humification of the soil organic matter was high. The humus was of the humate type in the upper horizons and of the fulvate-humate type in the lower horizons.     

Distribution pattern of total lipids and lipid fractions in forest humus

Mull, moder, and mor humus profiles were investigated for their total lipid contents and the behaviour of lipid-phosphorus and of five neutral lipid classes identified by HPTLC. The quantitative distribution of total and neutral lipids among the humus types is, besides by natural differences between the various parent litter materials, mainly controlled by soil physicochemical properties. In particular strongly acidic conditions, i.e. conditions corresponding to a reduced biological activity, inhibit significantly the decomposition of lipid compounds in (moder and) mor humus. A feature of the lipid depth functions is the input of microbial and root litter-derived lipid material in the fermentation layers and a considerable lipid accumulation in the A horizons, probably at least partly due to mechanical transport processes. Phospholipids show no distinct variation dependent on the humus type, as far as the organic layers are concerned. But obviously, lipid-P in the mineral, soil is closely correlated with, and therefore is a valuable measure for, the overall biological activity increasing from mor to moder and mull humus.     

Climatic effects on soil trophic networks and the resulting humus profiles in holm oak (Quercus rotundifolia) forests in the High Atlas of Morocco as revealed by correspondence analysis

Multivariate methods have been widely used for revealing the structures of communities, and in this paper we explore one particular method, namely correspondence analysis (also called reciprocal averaging), for studying humus profiles by the ‘method of small volumes’. The present study was done on humus profiles under holm oak (Quercus rotundifolia), an evergreen Mediterranean species, in the High Atlas of Morocco. Three sites (1500 m, 1700 m, 1900 m altitude) and 2 years (1999 and 2002) were compared. The humus form is Dysmull (mull with thick litter horizons), with variations in the thickness of the OL (entire leaves), OF (fragmented leaves with faecal pellets) and A (hemorganic) horizons according to altitude and year. The dead leaves are rapidly incorporated into holorganic (earthworm, insect) and hemorganic (enchytraeid) animal faeces, which form the bulk of the OF and A horizons. The S horizon (weathering parent rock) shows the greatest development of the root system. As altitude increases more fresh litter (OL) or more humified organic matter (OF, A) is accumulated. Variation from year to year is depicted by opposite differences in the amount of entire oak leaves and of dead roots. Humus components (classes) are used as active (main) variables, after standardization of their means and variances. The addition of numerous passive (additional) variables, standardized in the same way as active variables, enabled us to understand the influence of biological and climatic effects on the composition of humus profiles and soil trophic networks.     

Polycyclic aromatic hydrocarbons in different forest soils: Mineral horizons

The objective of this study was to assess the behavior of PAH in mineral soil horizons of different forest soils (Allersdorf, All: Inceptisol, mull humus type; Geisberg, Geis: Entisol, mull; Hohe Matzen, HoM: Spodosol, mor). At the mor site, the highest PAH loading was observed in the forest floor (HoM L to Oh, ΣX 20 PAH: 829 g ha^?1), whereas at the mull sites the humified mineral soil horizons were the main sink for PAH (All aAxh, Σ 20 PAH: 522 g ha^?1). In all soils, there was a significant PAH translocation into subsoil horizons (Σ 20 PAH in the subsoil: 76–195 g ha^?1). In order to delineate possible transport mechanisms, double-logarithmic relationships were established between the translocation of the distinct PAH from the surface soil to the subsoil and the PAH's K_ow values. The data suggested that transport of low-molecular PAH into the subsoil was primarily a function of the water solubility of each compound. In the biologically active All and Geis soils, high-molecular PAH were translocated independently from their K_ow value, and particle-bound transport probably by soil burrowing animals was assumed to control translocation of the penta- and hexacyclic PAH. In contrast, at HoM transfer of high-molecular PAH increased with increasing hydrophobicity, suggesting dissolved organic matter (DOM)-mediated transport of PAH. Fractionation of soil into a floatable fraction and into sand- (20–2000 μm), silt- (2–20 μm), coarse clay- (0.2–2 μm), and fine claysized (< 0.2 μm) separates revealed that more than 80% of the PAH loading could be assigned to silt- and coarse clay-sized separates, irrespective of the soil's texture (loamy sand to silty clay loam). Silt generally showed the highest C_org?related PAH concentrations. PAH profiles (relative proportion of each PAH on the sum of 20 PAH) revealed increasing proportions of high-molecular, more refractory PAH from the floatables and the sand-sized separates to the finer particles, corresponding with an increasing degree of SOM alteration in the same direction. At HoM, depth gradients of high-molecular PAH suggested co-transport of penta- and hexacyclic PAH with DOM and subsequent co-sorption selectively to the silt- and coarse-clay sized separates of the Bsh horizon.     

Postpyrogenic Polycyclic Soils in the Forests of Yakutia and Transbaikal region

Periodical forest fires are typical natural events under the environmental and climatic conditions of central and southern Yakutia and Transbaikal region of Russia. Strong surface fires activate exogenous geomorphological processes. As a result, soils with polycyclic profiles are developed in the trans-accumulative landscape positions. These soils are specified by the presence of two–three buried humus horizons with abundant charcoal under the modern humus horizon. This indicates that these soils have been subjected to two–three cycles of zonal pedogenesis during their development. The buried pyrogenic humus horizons accumulate are enriched in humus; nitrogen; total and oxalate-extractable iron; exchangeable bases (Са⁺² and Mg⁺²); and the fractions of coarse silt, physical clay (<0.01 mm), and clay (<0.001 mm) particles in comparison with the neighboring mineral horizons of the soil profile. The humus of buried pyrogenic horizons is characterized by the increased content of humic acids, particularly, those bound with mobile sesquioxides (HA-1) and calcium (HA-2) and by certain changes in the type of humus.     

Components of soil organic matter under grass and arable cropping

Components of the organic matter have been studied in three soils from adjacent sites with different long-term treatments: soil I, prolonged arable cultivation; soil II, 17 years under grass after prolonged arable cultivation; and soil III, old pasture. Contents of total organic C in the top 15cm were 0.9% in soil I. 1.7% in soil II and 4.8% in soil III. The light fraction, comprising partially decomposed materials with a specific gravity < 2.06, represented greater proportions of the organic C in soils II and III (20–23 per cent) than in soil I (8.5 per cent). The light fraction of soil III had a relatively high N content.The proportions of the soil organic C released, by hydrolysis, as neutral sugars, uronic acids, amino sugars, amino acids and phenolic acids were generally similar in the three soils, although uronic acids and phenolic acids constituted somewhat greater proportions in soils II and III than in I.The light fractions contained greater proportions of neutral sugars and phenolic acids, and smaller proportions of amino sugars and amino acids than the whole soils.     

Fluoride-induced changes in chemical properties and microbial activity of mull,moder and mor soils

Summary Fluoride-induced changes of chemical properties and microbial activities in humus soils were investigated in 12-week lysimeter experiments. The mull soil showed the highest F-adsorption capacity, in which 94% of the fluoride added was retained after addition of 4.5 mg F/cm² as NaF. The moder and mor soils only adsorbed 52% and 41%, respectively. F-additions induced leaching of organic matter, Fe, Al and P and increases in soil pH in the moder and mor. In contrast no Al, Fe and P was leached from the mull and only minor amounts of organic matter dissolved after a single application of 4.5 mg F/cm². Treatments with NaF up to 3700 mg F/kg did not significantly reduce respiration in any of the humus forms. Dehydrogenase, alkaline phosphatase and arylsulfatase activities as well as nitrification were inhibited at much lower F-additions in the moder and mor soils. A significant decrease in ammonification was observed in the moder. In contrast, microbial processes in the mull soil were not inhibited. This is due to its high adsorption capacity and the relatively low toxicity of F-ions. According to computations using GEOCHEM, the F-ion was the most abundant species in mull lysimeter leachates. Leachates of moder and mor soils contained mainly AIF-complexes (90%–99%). The lack of any effects from NaF treatment on soil respiration is attributed to the observed positive effects, e.g. dissolution of organic matter, desorption of P and increases in soil pH.     

Characteristics of soil organic matter in temperate soils by Curie point pyrolysis-mass spectrometry.

This series of papers examines some significant differences in the constitution of organic matter found amongst major soil groups and their genetic and morphological horizons, as determined by the dynamic pyrolysis-mass spectrometry of whole soil samples. Multivariate methods of data analysis identify groups of co-variant mass ions which successfully partition samples in terms of the above soil categories, and correlate with other major properties such as humification and hydromorphism. This first study covers the A horizons from a group of 22 Scottish soils chosen from the major temperate soil groups including brown forest soils, podzols, and noncalcareous, peaty and humic gleys (phaeozems, cambisols, podzols and gleysols). The principal components analysis of 52 mass ion intensities was found to partition the soils successfully in terms of two main factors which represented 62% of the total statistical variance. The first factor was found to correspond closely to the extent of hydromorphism, being high for highly gleyed A horizons, and depended chiefly on the presence of aromatic hydrocarbon ions. The second factor corresponded to the extent of mull humus formation, being high for brown forest soils (phaeozems, cambisols) and low for podzols, and depended chiefly on the abundance of polypeptide products relative to polysaccharide products. This second factor was evidently a more comprehensive expression of a humification factor found in previous studies. The relationships of these factors with C and N content and with base status properties were examined.     

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

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

Phenolic and carbohydrate signatures of organic matter in soils developed under grass and forest plantations following changes in land use

Comparisons were made between the phenolic and carbohydrate signatures of soil profiles developed under grass, spruce and ash stands. Samples were collected from a brown earth soil which was originally under the same land use, but over the past 43 years has supported different monocultures. Distinct signatures associated with each litter type were recorded in individual profiles. A relatively undecomposed phenolic fraction from lignin and hydrolysable carbohydrate fraction from plants had accumulated in the soils under spruce and ash. This largely reflected the quantity and quality of the litter inputs from the spruce and ash compared with the grass. The phenolic and hydrolysable carbohydrate fractions accounted for as much as 60% of the total organic carbon concentration in the deep horizons. In the grassland profile both fractions were more decomposed than under ash and spruce suggesting that the forest profiles had rapidly accumulated a carbon pool with a comparatively slow rate of decomposition. This was most apparent from the spruce profile (which contained 398 mg g^?1 C carbohydrate hydrolysed using trifluoracetic acid (TFA) in the C horizon compared with 165 and 45 mg g^?1 C under ash and grass respectively). We conclude that the decay rate of these fractions is a function of the vegetation type.     

Soils with complex organic profiles on the Vasyugan Plain

Soils with intricate patterns of their humus profiles developing in the neutral-calcium landscapes of the southern taiga of Western Siberia under highly dynamic paleogeographic, climatic, and weather conditions are characterized. The specific features of these soils comprise the diverse modern humus horizons along with the relic ones of different preservation rates, shallow leaching of carbonates, and a weak development of the middle-profile soil horizons. Specifying these organo-accumulative soils is substantiated by their high humus content against the geochemical background of the clayey calcareous parent rocks. The conjugated series of soils reflect different stages of the soil evolution (the humus profile degradation, the development of eluvial process, and the increase of contrasts in the acid-base conditions) and the hydromorphic transformation accompanied by the formation of organic horizons making the humus profile more complicated. In accordance with the diagnostic horizons, the position of the soils studied was determined in the Classification and Diagnostics of Soils of Russia. The relic enrichment of the humus horizon is proposed to be used as a specific feature of these soils.     

Fate of microbial residues in sandy soils of the South African Highveld as influenced by prolonged arable cropping

Long‐term cultivation of former grassland soils results in a significant decline of both living and dead microbial biomass. We evaluated the effect of duration of cropping on the preservation of fungal and bacterial residues in the coarse‐textured soils of the South African Highveld. Composite samples were taken from the top 20 cm of soils (Plinthustalfs) that have been cropped for periods varying from 0 to 98 years in each of three different agro‐ecosystems in the Free State Province. Amino sugars were determined as markers for the microbial residues in bulk soil and its particle‐size fractions. Long‐term cultivation reduced N in the soil by 55% and the contents of amino sugars by 60%. Loss rates of amino sugars followed bi‐exponential functions, suggesting that they comprised both labile and stable fractions. With increased duration of cropping the amino sugars attached to silt dissipated faster than those associated with the clay. This dissipation was in part because silt was preferentially lost through erosion, while clay particles (and their associated microbial residues) remained. Erosion was not solely responsible for the reduction in amino sugar concentrations, however. Bacterial amino sugars were lost in preference to fungal ones as a result of cultivation, and this effect was evident in both silt‐ and clay‐sized separates. This shift from fungal to bacterial residues was most pronounced within the first 20 years after converting the native grassland to arable cropland, but continued after 98 years of cultivation.