Fungal communities in the soils of early medieval settlements in the taiga zone

The difference between the mycobiota in anthropogenically transformed soils of the settlements of the 9th–14th centuries and in the background zonal Podzols and umbric Albeluvisols of the middle and southern taiga subzones in the European part of Russia is demonstrated. The mycological specificity of anthropogenically transformed soils with a cultural layer (CL) in comparison with the background soils is similar for all the studied objects. Its characteristic features are as follows: (1) the redistribution of the fungal biomass in the profile of anthropogenically transformed soils in comparison with zonal soils, (2) the lower amount of fungal mycelium in the CL with the accumulation of fungal spores in this layer, (3) the increased species diversity of fungal communities in the CL manifested by the greater morphological diversity of the spore pool and by the greater diversity of the fungi grown on nutrient media, (4) the change in the composition and species structure of fungal communities in the CL, (5) the replacement of dominant species typical of the zonal soils by eurytopic species, and (6) the significant difference between the fungal communities in the CL and in the above-and lower-lying horizons and buried soils of the same age. Most of the mycological properties of the soils of ancient settlements are also typical of modern urban soils. Thus, the mycological properties of soils can be considered informative carriers of soil memory about ancient anthropogenic impacts.     

Actinomycetal complexes in drained peat soils of the taiga zone upon pyrogenic succession

The number and diversity of actinomycetes in peat soils vary in dependence on the stage of pyrogenic succession. In the cultivated peat soil, the number of actinomycetes after fires decreases by three-four times, mainly at the expense of acidophilic and neutrophilic groups. An increase in the number of mycelial prokaryotes (at the expense of alkaliphilic forms) is seen on the fifth year of functioning of the pyrogenic peat soil. The species diversity of streptomycetes in peat soils also decreases after fires. An increase in the range of streptomycetal species at the expense of neutrophilic and alkaliphilic forms takes place on the fifth year of the pyrogenic succession. Parameters of the actinomycetal complex—the population density, species composition, and ecological features—are the criteria whose changes allow us to judge the state of peat soils in the course of their pyrogenic succession.     

Microbial biomass carbon in the profiles of forest soils of the southern taiga zone

In the mineral horizons of the soils under different southern taiga forests (oak, archangel spruce, and aspen in the Kaluzhskie Zaseki Reserve of Kaluga region and the green moss spruce and spruce-broadleaved forests of the Zvenigorod Biological Station of Moscow State University in Moscow region), the carbon content in the microbial biomass (C_mic), the rate of the basal respiration (BR), and the specific microbial respiration (qCO₂= BR/C_mic) were determined. The C_mic content was measured using the method of substrate-induced respiration (SIR). In the upper humus horizons of the soils, the C_mic content amounted to 762–2545 μg/g and the BR ranged from 1.59 to 7.55 μg CO₂-C/g per h. The values of these parameters essentially decreased down the soil profiles. The portion of C_mic in the organic carbon of the humus horizons of the forest soils was 4.4 to 13.2%. The qCO₂values increased with the depth in the soils of the Biological Station and did not change in the soils of the Reserve. The pool of C_mic and C_org and the microbial production of CO₂ (BR) within the forest soil profiles are presented.     

Microbial communities and transformation of carbon compounds in bog soils of the taiga zone (Tomsk oblast)

Two types of bogs were studied in Tomsk oblast—Maloe Zhukovskoe (an eutrophic peat low-moor bog) and Ozernoe (an oligotrophic peat high-moor bog). The gram-negative forms of Proteobacteria were found to be dominant and amounted to more than 40% of the total population of the microorganisms investigated. In the peat bogs, the population and diversity of the hydrolytic microbial complex, especially of the number of micromycetes, were lower than those in the mineral soils. The changes in the quantitative indices of the total microbiological activity of the bogs were established. The microbial biomass and the intensity of its respiration differed and were also related to the depth of the sampling. In the Zhukovskoe peat low-moor bog, the maximal biomass of heterotrophic microorganisms (154 μg of C/g of peat) was found in the aerobic zone at a depth of 0 to 10 cm. In the Ozernoe bog, the maximal biomass was determined in the zone of anaerobiosis at a depth of 300 cm (1947 μ g of C/g of peat). The molecular-genetic method was used for the determination of the spectrum of the methanogens. Seven unidentified dominant forms were revealed. The species diversity of the methanogens was higher in the oligotrophic high-moor bog than in the eutrophic low-moor bog.     

Automorphic taiga soils of the Sredneobskaya Lowland

The morphology of the profile, some chemical properties, and particle-size distribution of the automorphic soils developed from lacustrine-alluvial loamy-clayey deposits in the Sredneobskaya Lowland are considered. The soils of the West Siberian middle taiga zone remain poorly studied. A comparison of our data with data on podzolic soils in the northeastern part of European Russia and with diagnostic characteristics of the soil type of svetlozems included in the new classification system of Russian soils (2004) allows to argue that the studied soils cannot be classified as podzolic soils; most of them also do not fit the diagnostic criteria of svetlozems. The obtained data on the particle-size distribution in the studied soils do not agree with the concept of the sedimentation zonality in the West Siberian Plain.     

Changes in soil respiration in the course of the postagrogenic succession on sandy soils in the southern taiga zone

The dynamics of the CO₂ emission from sandy soils in the course of the postagrogenic succession in the southern taiga zone were studied. We measured total emission from the soil surface and, separately, respiration from the litter and mineral soil horizons during the warm (snowless) seasons of 2010 and 2011 on differently aged fallow plots: 0 years (cropland) and 7, 23, 55, 100, and 170 years. It was demonstrated that changes in the CO₂ emission in the course of the succession have a nonlinear pattern: the emission sharply increases in the first decade, then somewhat decreases, and then gradually increases again up to the maximum values. This is explained by the dependence of the rate of the emission on the soil carbon pools (humus + litter + underground phytomass) that are also subjected to nonlinear changes. Initially, the emission is mainly due to mineralization of labile organic substances added to the plowed soils in the form of organic fertilizers. Then, in parallel with a gradual increase in the pools of litter and underground phytomass, the total pool of soil organic carbon increases, and its role in the emission becomes more pronounced. The seasonal dynamics of the soil respiration are mainly controlled by the soil temperature; the soil moistening plays an important role only during the initial meadow stage of the succession.     

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.     

Microbial transformation of nitrogen compounds in middle taiga soils

The intensity of mineralization, nitrogen fixation, and denitrification in forest soils of the Karelian middle taiga ecosystems has been evaluated. Podzol-gleyish soil underlying a birch forest with gramineous plants and miscellaneous herbs was shown to have the highest nitrogen-fixing activity. The loss of gaseous nitrogen during denitrification was insignificant due to the low nitrifying activity of the soils named above. N₂O uptake by microorganisms was rather intensive in all the soils analyzed, and in illuvial-humo-ferric podzols underlying pine and spruce forests this process predominated. Podzolic sandy loam gley-like soil of a birch forest with gramineous plants and miscellaneous herbs had the highest potential for the mineralization of organic nitrogen; the rate of ammonification and nitrification in this soil was maximal.     

Comparison of field and laboratory measurement of denitrification and N2O production in the saturated zone of hydromorphic soils

We evaluated a new method to measure in situ denitrification under field conditions in a number of water-saturated subsoils that had a broad range of biogeochemical properties. A test solution containing ¹⁵NO₃⁻ and/or C₂H₂ was introduced to the subsoil and the subsequent production of dissolved denitrification products was measured to quantify denitrification activity. The method showed a clear production of denitrification products over time. Results were compared to laboratory-based measurements from the same soil incubated as anaerobic slurries with added ¹⁵NO₃⁻. Rates of denitrification with the in situ and the laboratory methods ranged from 1-2800 and 1-1700 μg N kg⁻¹ d⁻¹, respectively. Generally the methods gave good agreement and we consider both to be valid. However, there were some significant deviations, which we attribute to spatial heterogeneity and laboratory effects. Because the laboratory method is so much easier to perform, we suggest it should be the preferred method for large-scale studies of denitrification from the soil types we investigated. However, the two methods showed poor agreement in determining the proportion of N₂O in the total denitrification output. This was because this proportion is subject to delicate and complex control. We conclude that neither method was suitable for quantifying N₂O emission from the denitrification measurements.     

Methodologically controlled variations in laboratory and field pH measurements in waterlogged soils

We have tested the reliability and consistency of conventional pH measurements made on water‐soil mixtures with respect to sieving, drying, ratio of water to soil, and time of shaking prior to measurement. The focus is on a waterlogged soil where the preservation potential of archaeological artefacts is critical. But the study includes agricultural and forest soils for comparison. At a waterlogged site, laboratory results were compared with three different field methods: calomel pH probes inserted in the soil from pits, pH measurements of soil solution extracted from the soil, and pH profiles using a solid‐state pH electrode pushed into the soil from the surface. Comparisons between in situ and laboratory methods revealed differences of more than 1 pH unit. The content of dissolved ions in soil solution and field observations of O₂ and CO₂ concentrations were used in the speciation model PHREEQE in order to predict gas exchange processes. Changes in pH in soil solution following equilibrium in the laboratory could be explained mainly by CO₂ degassing. Only soil pH measured in situ using either calomel or solid‐state probes inserted directly into the soil was not affected by gas exchange processes. Variations on the order of 0.2–0.5 pH unit in different laboratory methods could not be explained by degassing and seem to be soil‐type specific and strongly influenced by drying and shaking. Further attention should be given to standardization of pH measurements, particularly before pH measurements from different soil types are compared.     

Difference in the pH values of hydromorphic soils in field and laboratory analyses

There are marked differences in the pH values determined in water suspension under laboratory conditions and in soil solution under field conditions in hydromorphic soils (gleysols and stagnosols). The value δpH = pH_susp–pH_sol can be either positive or negative. Among the main factors that affect the value of δpH are the laboratory preparation of soil samples and the suspension effect. The sign of the pH effect (value of δpH) depends on the participation of humus, carbonate, and exchange bases in the formation of aggregates destructed in the laboratory. The value of δpH is negative in noncalcareous soils with low content of exchangeable bases and fulvate composition of humus and positive in calcareous soils or soils enriched with exchangeable bases and humate composition of humus. In cases of a significant δpH effect, the value of pH_susp cannot be regarded as an adequate measure of soil acidity.     

The effect of dissolved organic substances on the genesis of gley-podzolic soils in the northern taiga zone,Arkhangelsk oblast

The effect of dissolved organic substances on the genesis and functioning of gley-podzolic soils in the lower reaches of the Northern Dvina River (Arkhangelsk oblast) has been studied. It is shown that polyphenols and low-molecular (<1000 a.u.) fractions of fulvic acids bound with Fe (II, III) and Mn (II) ions are present in the EL_g and B_fg horizons of these soils and participate in alternating downward and upward migration processes. The presence of these compounds colors the soil mass into the dark gray color resembling the color of the proper humus horizon.     

Ion transport through unsaturated soils: field experiments and regional simulations

This paper describes the movement of anions and cations through soils at the regional scale using block‐scale and regional simulations of one‐dimensional ion transport through cultivated soils. The simulations were based on field experiments in a region of about 10 km² in Lower Saxony, Germany. Transport was modelled with the convection–dispersion equation, and the cation exchange was described using the Gapon equation. We evaluated the spatial variation of cation exchange parameters, obtained estimates valid at the block scale, and simulated the one‐dimensional transport of anions and cations. The movement of anions and cations was simulated over blocks using effective transport parameters calculated from local transport parameters. The approach led to a good agreement between measured and predicted concentrations of Br^–, Na⁺, K⁺, Ca²⁺ and Mg²⁺ on four different 1 ha blocks. However, the mean concentrations of K⁺ in the soil solution in the uppermost horizons could not be described satisfactorily by the model. For the regional simulations, transport and exchange parameters were estimated by block kriging. All variograms of the exchange parameters were spatially structured with correlation lengths varying from 100 m to 300 m. Results of the regional simulations imply that Cl^– and K⁺ were transported substantially deeper in the southern part than in the northern part of the area. The transport depth of the ions strongly depended on the pore water velocities. The simulation of solute transport to the water table showed the influence of the depth of water table on the estimated travel times, superimposing the influence of the transport parameters in the region. The results of the regional simulations also emphasize the importance of careful fertilization, especially in regions with shallow water tables such as in the north of the area.     

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.     

Formation of polycyclic aromatic hydrocarbons in northern and middle taiga soils

An integrated study of the qualitative and quantitative composition of polycyclic aromatic hydrocarbons (PAHs) in the atmospheric precipitation-soil-lysimetric water system was performed using high performance liquid chromatography. It was shown that the accumulation of low-molecular PAHs (phenanthrene, anthracene, fluoranthene, pyrene, benz[a]anthracene, and chrysene) in soils is due to the transformation of organic matter and the regional transport and deposition of PAHs with atmospheric precipitation on the underlying surface. High-molecular polyarenes (benz[b]fluoranthene, benz[k]fluoranthene, benz[a]pyrene, dibenz[a,h]anthracene, benzo[ghi]perylene, and indeno[1,2,3-cd]pyrene) mainly result from the decomposition of soil organic matter.     

Biological activity of ant nests in the middle taiga zone

Ants are the most widespread social insects. Many species of ants influence a range of soil properties when building their nests in soil. The paper discusses the effects of ants on soil biological activity (nitrogen fixation, denitrification), as well as on biomass and the diversity of microorganisms. In many cases, these processes were more active in anthills. Changes in soil pH caused by nest-building activity of ants were also. There were no patterns in the distribution of pH values. Specific differences between microbial complexes of anthills and corresponding reference soils were revealed.     

Sorption of dimethylselenide by soils

Air-dry and moist soils were shown to possess the capacity to sorb substantial amounts of (⁷⁵Se)dimethylselenide produced by the yeast Candida humicola in culture, or by soil supplied with (⁷⁵Se)selenite, depending largely upon the organic matter content and selenium concentration of the soils. The sorption capacities of individual soil constituents followed the order; organic matter > clay minerals > manganese oxides > iron oxides > acid-washed sand.A chemical fractionation procedure applied to soils fumigated with (⁷⁵Se)dimethylselenide revealed that the majority of the selenium sorbed was converted after 1 month to other forms, extractable mainly with strong acid solutions. Experiments with sterilized (autoclaved and γ-irradiated) soils indicated that soil microorganisms played little, if any, part in the sorption process.The work reported here indicates that soil is an important natural “sink” for atmospheric dimethylselenide.     

Sorption and fate of perchlorate in arid soils

The mobility of perchlorate in soils depends on several factors, including soil mineralogy and the presence of other oxyanions that compete with perchlorate for the retention sites. Currently, there are no studies that evaluate the mobility of perchlorate in arid soils. The present study evaluated the mobility of ClO₄^– in three arid soils, Canchones, Humberstone and Pica, exposed to two ClO₄^– concentration ranges and different ionic strengths. In Humberstone (non-agricultural) and Pica (agricultural) soils, the sorption processes were not important for both concentration ranges, while Canchones soil (agricultural) showed a decrease in perchlorate concentration associated with microbial degradation processes. The increase of medium ionic strength by addition of Ca(NO₃)₂ only had an important effect on Humberstone soil, associated with the presence of kaolinite and muscovite (variable charge). A competition effect was observed between perchlorate, nitrate and other anions presents in solution by absorption sites generated from variable charge mineral and calcium. Considering the quite low sorption capacity of the soils and the high solubility, perchlorate can be absorbed by fruit and vegetables of export in concentrations over the healthy levels established by international organization.