A new method to determine the carbon content of water-soluble organic compounds in soils

The possibility to use the oxidation rate of different waters by dichromate as measured by photometry for the determination of the organic carbon content in water extracts from the organic horizons of soddy-podzolic soils (in the Republic of Komi) was confirmed. The advantages of the method proposed are discussed.     

Sulfate adsorption by variable charge soils: Effect of low-molecular-weight organic acids

Sulfate (SO₄ ^2–) movement and transport in soils has received considerable attention in recent years. In most soils, SO₄ ^2– coexists with a variety of natural organic compounds, especially organic acids. Studies were conducted to assess the effect of low-molecular-weight organic acids (eight aliphatic and five aromatic acids) on SO₄ ^2– adsorption by variable charge soils from Chile and Costa Rica. The effects of type of organic acid, pH, type of soil, and organic acid concentration were investigated. In one experiment, a 1.0 g soil sample was equilibrated with 25 ml 0, 0.5, 1.0, 2.0, 4.0, or 6.0 mM K₂SO₄ in 1 mM NaCl in the presence or absence of 5 mM citric acid. In the second set of experiments, the adsorption of 2 mM SO₄ ^2– in soils at pH 4 or pH 5 in the presence or absence of one of 13 organic acids at a concentration of 2 mM or 5 mM was studied. Results showed that citric acid significantly decreased SO₄ ^2– adsorption by the two soils. Sulfate adsorption decreased with increasing pH of the equilibrium solution. Aliphatic acids, with the exception of cis-aconitic acid, decreased the amount of SO₄ ^2– adsorbed by the two soils, with oxalic, tartaric, and citric acid showing the greatest effect. The differences in pH values of the equilibrium solutions in the presence and absence of organic acids were significantly, but negatively, correlated with the amount of SO₄ ^2– adsorbed, suggesting chemisorption of SO₄ ^2– and the release of hydroxide ions. The ionization fraction values of the organic acids at the equilibrium pH were correlated with the amounts of SO₄ ^2– adsorbed, suggesting that the protonation of surface hydroxyl groups of the mineral phase increased as the strength of the ionization of the acid increased, thus creating more positively charged surfaces. Received: 12 February 1997     

Psychrotolerant actinomycetes of plants and organic horizons in tundra and taiga soils

It has been revealed that in organic horizons and plants of the tundra and taiga ecosystems under low temperatures, actinomycetal complexes form. The population density of psychrotolerant actinomycetes in organic horizons and plants reaches tens and hundreds of thousands CFU/g of substrate or soil, and decreases in the sequence litters > plants > soils > undecomposed plant remains > moss growths. The mycelium length of psychrotolerant actinomycetes reaches 220 m/g of substrate. Application of the FISH method has demonstrated that metabolically active psychrotolerant bacteria of the phylum Actinobacteria constitute 30% of all metabolically active psychrotolerant representatives of the Bacterià domain of the prokaryotic microbial community of soils and plants. Psychrotolerant actinomycetes in tundra and taiga ecosystems possess antimicrobial properties.     

Effect of the natural reforestation of an arable land on the organic matter composition in soddy-podzolic soils

The dynamics of the organic matter composition in soddy-podzolic soils during the natural reforestation of an arable land in the southern taiga zone have been discussed. It has been shown that the contents of the total and labile carbon in the old plow horizon increase with the age of the fallow in the chronosequence of soils established in the Parfen’evo district of Kostroma oblast. The parameters characterizing the labile soil organic matter include the contents of the carbon extractable by mild chemical extractants (distilled water, 0.1 M K₂SO₄ solution, 0.1 M neutral Na₄P₂O₇ solution), the microbial biomass, and the light fraction. The granulo-densimetric fractionation has shown that the contents of carbon in the light and organomineral fractions of the soil vary in the course of the postagrogenic succession. The content of the clay-fraction carbon increases and its portion in the total carbon of the soil decreases at the transition from the plowland to the forest. The reforestation of agrosoddy-podzolic soils enhances the physical protection of the soil organic matter due to the increase in the portion of microaggregate carbon.     

Molecular composition of humic substances in tundra soils (13C-NMR spectroscopic study)

Functional groups and molecular fragments of humic substances (HSs) from cryohydromorphic peat gley tundra and surface-gley tundra soils have been identified by ¹³C-NMR spectroscopy. The analysis of HS preparations has shown that the molecules of humic acids (HAs) are enriched with aromatic fragments compared to fulvic acids (FAs). Aliphatic chains, carbohydrate- and amino acid-type structures prevail in the carbon skeleton of the FAs. An integrated parameter of the HS hydrophobicity has been proposed. The parameter represents the total portion of unoxidized carbon atoms and allows indirectly assessing the amphiphilic properties of HSs.     

Features of cryogenic environment in soils of continental tundra and arid steppe on the southern Khangai slope under electron microscope

Morphoscopic studies were conducted with the aid of SEM and TEM microscopes, on quartz grains and fractions not exceeding 2 μm, on soil samples from the continental tundra, alpine meadow and arid steppe. The aim of these studies was to define the features and properties of the quartz grains and fractions, produced by the environment of the cryoarid continental climate of Central Asia. It has been established that in cold and humid climates processes of cryogenic and hydrothermic splitting occur on the surface of quartz grains and in cold and dry climates processes of cryothermic scalling. The increase in the surface area of disintegrated minerals under continental climate conditions is accompanied by cryochemical coating by mineral-organic compounds.     

Dynamics of acid-soluble iron compounds in soddy-podzolic soils of the southern Komi Republic

The content of total iron and its contents in the Tamm, Mehra-Jackson, and 1 N H₂SO₄ extracts were determined for arable and forest soddy-podzolic soils with different degrees of gleyzation. The seasonal dynamics of the acid-soluble iron compounds in the soils were studied. It was found that the amount of iron extractable by 1 N H₂SO₄ was smaller than that passing into the Tamm and Mehra-Jackson solutions. The seasonal variation of the acid-soluble iron compounds in the humid years was significantly higher than in the dry years; it depended on the hydrological conditions of the year of observations and the soil density and degree of gleyzation. The temperature conditions of the year of observations had a lower effect on the content of the acid-soluble iron. The profile distributions of the acid-soluble and total iron depended on the vertical and lateral migration of water, as well as the meso- and microrelief conditions. An increase in the content of acid-soluble iron was observed under the decreased temperature in the spring and fall. The mobilization of iron under the effect of podzolization was activated during the period of the summer rains. In the third year of the agricultural development, the content of acid-soluble iron in the soils slightly decreased, which could be indicative of a decrease in the content of iron involved in the biological cycle under the development and drainage conditions. An exception was provided by the arable soils on the toeslope, where the content of acid-soluble iron was higher than that in the forest soils occupying analogous positions in the relief.     

Effect of wetting conditions on the fractional composition of heavy metal compounds in agrosoddy-podzolic soils contaminated with sewage sludge

Excessive wetting significantly affects the physicochemical, chemical, and biological properties of soils and changes the valence of Fe and Mn and the fractional composition of their compounds, as well as the compounds of the microelements and heavy metals bound to them. It was found that the metals are subdivided into three groups with respect to the soil wetting conditions: (1) the iron-group metals, the state of which is determined by the soil wetting conditions, the development of the reduction processes, and the status of the Fe and Mn compounds as the main sorption complexes closely bound to Co and Ni; (2) the Cu and Pb compounds, the status of which depends on the soil wetting and redox conditions and which are closely bound to organic matter and Fe and Mn compounds; and (3) the Zn and Cd compounds, the status of which little depends on the soil wetting and redox conditions and which are characterized by a low affinity for Fe, Mn, and organic compounds.     

Psychrotolerant actinomycetes in soils of the tundra and northern taiga

Actinomycetes adapted to low-temperature conditions are present in the cold soils of the tundra and northern taiga in quantities comparable to mesophylic forms and dominate in the soil actinomycete complex. Actinomycetes isolated from cold soils were identified as Streptomyces. Most actinomycetes relate to psychrotolerant forms according to habitation temperature. Two of them are conditionally psychrophilic. Specific properties of the investigated populations were identified by multirespirometrical testing.     

Relationship between lead uptake by lettuce and water-soluble low-molecular-weight organic acids in rhizosphere as influenced by transpiration

The relationship between Pb uptake by leaf lettuce ( Lactuca sativa L.) and water-soluble low-molecular-weight organic acids (LMWOAs) in rhizosphere, as influenced by transpiration (high and low), has been studied. Studies were carried out by culturing lettuce plants grown for 2 weeks in pots filled with quartz sand mixed with anion-exchange resin and then for 30 days in a greenhouse. The potted lettuce plants were subjected to stress by the addition of Pb(NO 3) 2 solutions (100, 200, and 300 mg of Pb L (-1)) and by high and low transpiration treatments for another 10-day period. Blank experiments (without addition of Pb(NO 3) 2 solutions to the pots) were also run. There were no significant differences in the growth of the plants with the addition of Pb(NO 3) 2 solutions in either of the transpirations studies. Uptake of Pb by the shoots and roots of the plants was found to be proportional to the concentration of Pb solutions added, and more accumulation was observed in the roots than in the shoots at the end of days 3 and 10. High transpiration caused more Pb uptake than did low transpiration. One volatile acid (propionic acid) and nine nonvolatile acids (lactic, glycolic, oxalic, succinic, fumaric, oxalacetic, d-tartaric, trans-aconitic, and citric acids) in rhizosphere quartz sand or anion-exchange resin were identified and quantified by gas chromatography analysis with a flame ionization detector. The amount of LMWOAs in rhizosphere quartz sand or anion-exchange resin increased with higher amounts of Pb in quartz sand solution and also with longer duration of the study. The total quantities of the LMWOAs in the rhizosphere quartz sand or anion-exchange resin were significantly higher under high and low transpiration with a 300 mg of Pb L (-1) solution addition at the end of day 10. Compared with our previous related studies (published work), the present study shows that the presence of LMWOAs in rhizosphere does not significantly affect Pb uptake by lettuce plants under high and low transpiration. A physiological mechanism of the roots of lettuce plants governing the relationship between Pb contamination level and quantity of water-soluble LMWOAs in rhizosphere quartz sand and resin, as influenced by transpiration, was proposed.     

Mobile aluminum compounds in soils of the southern taiga (soils of the central forest reserve as an example)

The profile distributions of aluminum extracted by the Tamm and Bascomb reagents and of the exchangeable aluminum were studied in soils of automorphic, transitive, and accumulative positions in the landscapes of the southern taiga. In the mineral horizons of the gleyic peaty-podzolic soils developed on poorly drained flat surfaces and in the floodplain soils, the distribution of oxalate- and pyrophosphate-soluble aluminum has a strongly pronounced accumulative character. In the podzolic soils of the automorphic positions and slopes, an eluvial-illuvial distribution was characteristic with the maximal aluminum content in the podzolic horizons. The strong differentiation of the upper part of the profile in the automorphic podzolic soils in terms of the Al content in the Tamm and Bascomb extracts is mainly related to an increase of the pedogenic chlorite content upon the transition from the AE to the E horizon. In the podzolic horizons of these soils, aluminum can accumulate in the form of proto-imogolite structures. The exchangeable aluminum displays an accumulative type of distribution. On the basis of calculating the reserves of the different aluminum compounds, two main accumulative zones for the mobile compounds of this element were recorded in the soils of the landscapes studied: the E horizon in the automorphic podzolic soils, where Al accumulates as soil chlorite or, probably, as proto-imogolite, and the A1 horizon of the floodplain soils, where Al accumulates in aluminoorganic complexes.     

Dissolved organic matter in lysimetric water of mountain forest soils in the southern Sikhote Alin

The fractional composition of dissolved organic matter and the chemical nature of humic and fulvic acids were studied in lysimetric waters from forest soils of different altitudinal zones in the Sikhote Alin Range. The elemental composition, infrared absorption spectra, concentrations of acid functional groups, and pK spectra of humic and fulvic acids were determined. Fulvic acids predominated in the upper soil horizons, and fraction of nonspecific dissolved organic substances predominated in the lower mineral horizons. The portion of humic acids in the humus horizons markedly decreased from the low-mountain soils to the high-mountain soils; the nitrogen content of humic and fulvic acids decreased in the same direction. Three classes of carboxyl and phenolic groups were determined in pK-spectra of humic and fulvic acids. The soils of high-mountain zones had stronger acidic properties of humic and fulvic acids in comparison with the soils of low-mountain zones. The determined characteristics of the composition of dissolved organic matter and the trends of their changes contribute to our knowledge of pedogenetic processes in the altitudinal sequence of forest landscapes of the Sikhote Alin Range.     

Individual organic compounds in water extracts from podzolic soils of the Komi Republic

The contents of organic compounds in water extracts from organic horizons of loamy soils with different water contents from the medium taiga zone of the Komi Republic were determined by gas-liquid chromatography and chromatography-mass spectrometry. The mass concentration of organic carbon in the extracts was in the range of 290?C330 mg/dm³; the mass fraction of the carbon from the identified compounds was 0.5?C1.9%. Hydrocarbons made up about 60% of the total identified compounds; acids and their derivatives composed less than 40%. Most of the acids (40?C70%) were aliphatic hydroxy acids. The tendencies in the formation of different classes of organic compounds were revealed depending on the degree of the soil hydromorphism. The acid properties of the water-soluble compounds were studied by pK spectroscopy. Five groups of compounds containing acid groups with similar pK_a values were revealed. The compounds containing groups with pK_a < 4.0 were predominant. The increase in the surface wetting favored the formation of compounds with pK_a 3.2?C4.0 and 7.4?C8.4.     

The elemental composition and amphiphilic properties of humic acids in southern taiga soils

This paper gives the characteristics of the elemental composition and amphiphilic properties of humic acids (HAs) extracted from different horizons of the most typical soils in the Central Forest Biosphere Reserve (CFBR, the Tver Oblast). An attempt at characterizing some properties of the structure of HAs is made based on the data of the elemental composition. The data on amphiphilic properties enable one to reveal whether components that are capable of migration are present.     

Soil microbial biomass and organic matter composition in soils under cultivation

To determine whether there is a relationship between the composition of soil organic matter and the activity of the soil microbial biomass, the composition of the organic matter in 12 typical arable soils in Northwest Germany was investigated by wet chemical analysis and CPMAS cross polarization magic angle spinning ¹³C-NMR spectroscopy. The data were correlated with the microbial biomass as estimated by substrate-induced respiration. A strong correlation between the microbial biomass and alkylic C compounds was observed (r=-0.960^***). Recalcitrant substances were enriched in this fraction, which were classified as humic acids according to the wet chemical procedure. The microbial decomposition of these humic acids is probably retarded, due to their chemical structure and/or physical bonding, when the soil microbial biomass activity is limited.     

Fractional composition of lead compounds in soils of Moscow and Moscow region

Sequential fractionation of lead compounds from the urban and suburban soils of Moscow and eastern Moscow region was performed using the Tessier method. It was found that strongly bound lead compounds retained by Fe and Mn hydroxides were predominant in the background (reference) soils of the Meshchera Lowland in Moscow oblast. The content of almost all the lead fractions, except for the hydroxide fraction, increased in the contaminated soils. The quantitative proportions of the particulate fractions varied depending on the distance from the city, the physicochemical properties of the soils, and the land use. The profile distribution of the lead was of accumulative character; the metal was fixed on the biogeochemical barrier, where the lead compounds of the fourth fraction bound to organic matter are mainly accumulated.     

Composition of humus in chronosequences of buried soils in the tundra zone

The humus characteristics in buried Holocene and Late Pleistocene paleosols of the tundra zone have been studied. It is shown that the paleosol sequences encompassing the time span from 55 to 2.5 ka BP contain paleosols with analogous types of humus, attesting to the cyclic repeatability of the corresponding stages of soil formation. A tendency for an increase in the degree of humification in the course of soil development has been revealed. Within the ultracontinental areas of East Siberia, the accumulation of salts accompanied soil formation in the Late Pleistocene and Holocene.     

Influence of low-molecular-weight organic acids on the solubilization of phosphates

A range of low-molecular-weight organic acids were identified in rhizosphere soil, leaf litter, and poultry manure compost. Laboratory and greenhouse experiments were carried out to examine the effects of seven low-molecular-weight organic acids on phosphate adsorption by soils, and the solubilization and plant uptake of P from soil pre-incubated with monocalcium phosphate and North Carolina phosphate rock. Acetic, formic, lactic (monocarboxylic), malic, tartaric, oxalic (dicarboxylic), and citric (tricarboxylic) acids were used in the study. The addition of organic acids decreased the adsorption of P by soils in the order tricarboxylic acid>dicarboxylic acid>monocarboxylic acid. The decreases in P adsorption with organic acid addition increased with an increase in the stability constant of the organic acid for Al (logK _Al). Organic acids extracted greater amounts of P from soils meubated with both monocalcium phosphate and phosphate rock than water did. Although more phosphate was extracted by the organic acids from monocalcium phosphate — than from phosphate rock — treated soils in absolute terms, when the results were expressed as a percentage of dissolved phosphate there was little difference between the two fertilizers. The amount of P extracted by the organic acids from both fertilizers increased with an increase in logK _Al values. The addition of oxalic and citric acids increased the dry matter yield of ryegrass and the uptake of P in soils treated with both fertilizers. The agronomic effectiveness of both fertilizers increased in the presence of organic acids and the increase was greater with the phosphate rock than with the monocalcium phosphate. The results indicated that organic acids increase the availability of P in soils mainly through both decreased adsorption of P and increased solubilization of P compounds.     

Phosphorus compounds in subarctic Fennoscandian soils at the mountain birch (Betula pubescens)—tundra ecotone

Nutrient availability will partly regulate the response of high latitude ecosystems to climate warming, but phosphorus biogeochemistry is poorly understood in Arctic soils. We used NaOH-EDTA extraction and solution ³¹P nuclear magnetic resonance (NMR) spectroscopy to determine phosphorus compounds in subarctic soils from three locations in the Fennoscandian mountains contrasting in latitude and continentality. Soils were taken from open tundra and mountain birch (Betula pubescens Ehrh.) forest at each location. Between 87 and 95% of the total phosphorus was extracted from the surface 2 cm of the organic soil horizons. Most of the extracted phosphorus was orthophosphate monoesters (44-55%), with smaller concentrations of inorganic orthophosphate (15-24%), orthophosphate diesters (12-16%), pyrophosphate (3-18%), inorganic polyphosphate (0-15%) and phosphonates (0-4%). The orthophosphate diesters were further subclassified into DNA (9-13% extracted phosphorus) and phospholipids (1-6% extracted phosphorus), although strong signals in the orthophosphate monoester region of the spectra, consistent with the degradation of phosphatidyl choline in alkaline solution, suggested that phospholipid concentrations were substantially underestimated. The phosphorus composition was broadly similar among soils from the three locations, although no phosphonates were detected in tundra soils from the most southerly site. Deeper organic horizons tended to contain a greater proportion of orthophosphate monoesters than at the surface. The abundance of phosphorus compounds that would be considered readily degradable in temperate environments probably reflects the slow organic matter decomposition in these cold, acidic soils, and suggests that phosphorus availability is unlikely to limit ecosystem productivity on mesic soils at the birch-tundra ecotone during changes induced by climate warming.     

Carbon in tundra soils in the Lake Labaz region of arctic Siberia

Large amounts of carbon are stored in permafrost‐affected soils of the Arctic tundra. The quantity, distribution and composition of this carbon are important, because much of the carbon is likely to be released as a result of global warming. We have studied soils of the central Siberian Arctic to determine the carbon content and the nature of the organic matter by density fractionation, and ¹³C‐NMR‐ and ¹³C‐stable‐isotope analyses. There are pronounced differences in the profile and variations from place to place in the quantity and nature of soil organic matter. We estimated that the mean stock of carbon was 14.5 kg m^–2 within the active layer. We found a total of about 30.7 kg C m^–3 in the entire upper metre of the soils. Carbon of the tussock tundra showed strong vertical differentiation, with a large proportion comprising decomposed, recalcitrant compounds. We identified within the soil several zones of aerobe and anaerobe decomposition. Mobile carbon fractions have precipitated under the influence of low temperatures.