Global climate changes and the soil cover

The relationships between climate changes and the soil cover are analyzed. The greenhouse effect induced by the rising concentrations of CO₂, CH₄, N₂O, and many other trace gases in the air has been one of the main factors of the global climate warming in the past 30–40 years. The response of soils to climate changes is considered by the example of factual data on soil evolution in the dry steppe zone of Russia. Probable changes in the carbon cycle under the impact of rising CO₂ concentrations are discussed. It is argued that this rise may have an effect of an atmospheric fertilizer and lead to a higher productivity of vegetation, additional input of organic residues into the soils, and activation of soil microflora. Soil temperature and water regimes, composition of soil gases, soil biotic parameters, and other dynamic soil characteristics are most sensitive to climate changes. For the territory of Russia, in which permafrost occupies more than 50% of the territory, the response of this highly sensitive natural phenomenon to climate changes is particularly important. Long-term data on soil temperatures at a depth of 40 cm are analyzed for four large regions of Russia. In all of them, except for the eastern sector of Russian Arctic, a stable trend toward the rise in the mean annual soil temperature. In the eastern sector (the Verkhoyansk weather station), the soil temperature remains stable.     

Microbial activity of peat soils of boggy larch forests and bogs in the permafrost zone of central Evenkia

The microbial activity of peat soils was studied in boggy larch forests and in an oligo-mesotrophic bog in the basins of the Kochechum and Nizhnaya Tunguska rivers (central Evenkia). It was found that the organic matter transformation in the peat soils of all the plots is mainly performed by oligotrophic bacteria composing 88–98% of the total bacterial complex. The major contribution to the organic matter destruction belonged to the heterotrophic microorganisms, the activity of which depended on the permafrost depth and the soil temperature, the soil acidity, and the botanical composition of the peat. Peat soils were characterized by different activities as judged from their microbiological and biochemical parameters. The functioning of microbial communities in the studied ecotopes of the permafrost zone was within the range of natural variations, which pointed to their ecological stability.     

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.     

Soils of northern spurs of the Cherskii Ridge in the area of the northern pole of cold: Morphology,properties, and classification

The soils in the area of the northern pole of cold located on the interfluve between the Yana and Adycha rivers within the spurs of Kisilyakh Ridge included in the mountain system of Cherskii Ridge have been studied for the first time. The profile-genetic approach has been applied to describe the soils and determine their classification position. It is found that the major soil types in this region are the soils of the postlithogenic trunk belonging to the orders of lithozems (Cryic Leptosols), gley soils (Gleyic Skeletic Cryosols), and Al–Fe-humus soils (Spodic Skeletic Cryosols). The ecological ranges of altitudinal zones— the taiga zone with various types of lithozems below 630–700 m a.s.l. and the tundra zone with combinations of gley and nongley cryogenic soils above these heights—have been established. The development of gley or nongley soils is specified by the local orogenic and lithological conditions and slope aspect, which, in turn, control the degree of drainage and the presence and character of permafrost. In the profile of mountainous gley soils (gleyzems) with shallow ice-rich permafrost, cryogenic processes and features typical of the analogues of these soils on plains—cryogenic cracking, cryoturbation, solifluction, thixotropy, oxiaquic features above permafrost, saturation of the soil profile with mobile humus, etc.—are typical.     

Increased snow depth affects microbial activity and nitrogen mineralization in two Arctic tundra communities

Microbial activity in Arctic tundra ecosystems continues through the winter and is an important component of the annual C budget. This activity is sensitive to climatic variation, particularly snow depth because that regulates soil temperature. The influence of winter conditions on soil N cycling is poorly understood. In this study, we used intact core incubations sampled periodically through the winter and following growing season to measure net N mineralization and nitrification in dry heath and in moist tussock tundra under ambient and experimentally increased snow depths (by use of a snowfence). In dry heath, we sampled soils under Dryas octopetela or Arctostaphylos alpine, while in tussock tundra, we sampled Eriophorum vaginatum tussocks and Sphagnum dominated areas between tussocks. Our objectives were to: (1) examine how different winter snow regimes influenced year-round N dynamics in the two tundra types, and (2) evaluate how these responses are affected by dominant species present in each system. In tussock tundra, soils with increased winter snow cover had high net N mineralization rates during the fall and winter, followed by immobilization during thaw. In contrast, N mineralization only occurred during the autumn in soils with ambient snow cover. During the growing season when N immobilization dominated in areas with ambient snow cover, soils with increased winter snow cover had positive net mineralization and nitrification rates. In dry heath tundra, soils with increased snow depth had high late winter net N mineralization rates, but these rates were: (a) comparable to early winter rates in soils under Arctostaphylos plants with ambient snow cover; (b) greater in soils under Arctostaphylos plants than in soils under Dryas plants; and (c) less than the rates found in tussock tundra. Our findings suggest under ambient snow conditions, low soil temperatures limit soil N mineralization, but that deeper snow conditions with the associated warmer winter soil temperatures dramatically increase over-winter N mineralization and thereby alter the amount and timing of plant-available N in tundra ecosystems.     

Approaches to the Classification of Soils of the Accumulative Seashores of Russian Northeast

Eurasian Soil Science - A specific group of diverse marsh soils forming on sea coasts in the permafrost zone is proposed to be included into the Russian soil classification system. These soils are...     

Organic carbon and total nitrogen variability in permafrost-affected soils in a forest tundra ecotone

Soils of the high latitudes are expected to respond sensitively to climate change, but still little is known about carbon and nitrogen variability in them. We investigated the 0.44‐km² Little Grawijka Creek catchment of the forest tundra ecotone (northern Krasnoyarsk Krai, Russian Federation) in order (i) to relate the active‐layer thickness to controlling environmental factors, (ii) to quantify soil organic carbon (SOC) and total nitrogen (NT) stocks, and (iii) to assess their variability with respect to different landscape units. The catchment was mapped on a 50 × 50 m grid for topography, dominant tree and ground vegetation, organic‐layer and moss‐layer thickness, and active‐layer thickness. At each grid point, bulk density, and SOC and NT concentrations were determined for depth increments. At three selected plots, 2‐m deep soil cores were taken and analysed for SOC, NT and ¹⁴C. A shallow active layer was found in intact raised bogs at plateaux situations and in mineral soils of north‐northeast (NNE) aspect. Good drainage and greater solar insolation on the south‐southwest (SSW) slopes are reflected in deeper active layers or lack of permafrost. Organic carbon stocks to a soil depth of 90 cm varied between 5 and 95 kg m^–2. The greatest stocks were found in the intact raised bogs and on the NNE slopes. Canonical correspondence analysis indicates the dominant role of active‐layer thickness for SOC and NT storage. The 2‐m soil cores suggest that permafrost soils store about the same amount of SOC from 90 to 200 cm as in the upper 90 cm. Most of this deep SOC pool was formed in the mid‐Holocene (organic soils) and the late Pleistocene (mineral soils). Our results showed that even within a small catchment of the forest tundra, active‐layer thickness and, hence, SOC and NT storage vary greatly within the landscape mosaic. This has to be taken into account when using upscaling methods such as remote sensing for assessing SOC and NT storage and cycling at a regional to continental level.     

Thermal regime of tundra soils under reclamation and restoration of natural vegetation

This paper covers the specifics of the temperature regime in reclaimed tundra soils under a sown perennial herb meadow and a restored (secondary) ecosystem as compared to the small-shrub yernik (birch)-willow-moss and shrub yernik-willow-moss tundra types. The taxonomic position of the anthropogenic soils and those of the secondary (restored) biogeocenosis is discussed as related to the transformation or regeneration of the biotic and thermal components of the biogeocenosis. The soil development causes profound changes in the freezing-thawing regime, which gives grounds to distinguish the developed soils as an individual soil type.     

Electrical resistance profiles of permafrost-affected soils in the north of Western Siberia according to their vertical electrical sounding

Vertical electrical sounding (VES) of soils and underlying permafrost was performed on key plots in the north of Western Siberia (the Yamalo-Nenets Autonomous Okrug). It was supposed that the values of apparent electrical resistivity should sharply change at the boundary between the active layer and permafrost. Gleyzems, peat gleyzems, podzols, and petrozems studied on the key plots within the Yamal and Gydan peninsulas were characterized by different depths of the active layer. It was found that the electrical resistivity in the permafrost is one to two orders of magnitude higher than that in the active layer of the soils of different textures. Our study suggests that the VES method can be used to diagnose permafrost without disturbance of the soil cover. This conclusion is of special interest for long-term permafrost monitoring programs on permanent key plots. In general, the data obtained by VES are in agreement with the results of determination of the active layer thickness by traditional field methods.     

Changes in the temperature regime of podzolic soils in the course of natural forest restoration after clearcutting

The results of temperature monitoring in podzolic soils under the middle-taiga bilberry spruce forest and secondary mixed forest of the Komi Republic performed in 2008–2014 are presented. The changes in characteristics of soil temperature in the litter horizon and in the mineral horizons at the depths of 20 and 50 cm are outlined. It is shown that soil temperature regimes differ under the native spruce forest, young growth, and middle-aged secondary mixed forest. The soils of secondary phytocenoses are warmed up to a greater depth and are characterized by the higher heat supply. The differences are seen in a number of temperature parameters, such as the accumulated temperatures above 5°C and above 10°C at the depths of 20 and 50 cm. The most significant differences between the studied plots manifest themselves in the values of temperature amplitudes during the warm season. Maximum values of daily temperature amplitudes were obtained on the plot under young growth, whereas the soil under the middle-aged mixed forest was characterized by minimum values of daily temperature amplitudes.     

Soils of the forest-tundra ecotone in the Khoseda-Yu River basin of the Bol’shezemel’skaya tundra

A detailed characterization of soils in the upper reaches of the Khoseda-Yu River (the Bol’shezemel’skaya tundra in the northeast of European Russia) is given. The classification position of these soils is considered. The specificity of soil formation under tundra communities and under forest groves within the tundra zone is examined. The polygenetic nature of the studied soils is shown; it is explained by the repeated shifts of zonal boundaries within the forest-tundra ecotone.     

Decomposition rates of buried substrates increase with altitude in the forest-alpine tundra ecotone

Decomposition rates were measured across the forest-alpine tundra ecotone on two mountains in the Colorado Front Range. Cotton strips decomposed in the surface soils of forest, krummholz, and tundra plots for one year. We expected decomposition rates to decline with altitude or be most rapid in the krummholz. Surprisingly, decomposition rates increased from forest to tundra on Mt. Evans and remained constant across the ecotone on Niwot Ridge, highlighting differences in biogeochemical processes between two nearby mountains with otherwise similar alpine and subalphine ecosystems. Our results support the concept that decomposition rates exhibit a curvilinear relationship with soil temperature and moisture. However, soil moisture was found to be the primary factor controlling cellulose decomposition rates in soils in the forest-alpine tundra ecotone. Cellulose decomposition rates increased with soil depth indicating greater microbial activity in the mineral soil than in the organic horizon due to greater soil moisture. In addition to microbial activity, decomposition rates in the tundra may be enhanced by physical degradation from freeze-thaw events and vigorous root growth.     

Procedural Approaches to Field Determination of Root and Microbial Respiration Contribution to CO<Subscript>2</Subscript> Emission by Permafrost-Affected Soils

In the discontinuous cryolithozone in the north of Western Siberia in forest and tundra biogeocoenoses, two field methods for individual determination of root and microbial soil respiration were tested: plant shading and root exclusion (comparison of the plots with vegetation and without it). The proportion of of root respiration in the total soil respiration in the forest biogeocoenosis was 7–50%; in the tundra, 10–50%. The plant shading method has been physiologically substantiated, is the least time-consuming, and the least damaging to soil function (moisture and temperature do not change). The proposed modification of the method (root exclusion on natural objects) demonstrated a satisfactory result, but it is not universal due to the specifics of objects.     

Soil carbon pools in tundra and taiga ecosystems of northeastern Europe

The mean pools of soil carbon were determined for the first time for twelve soil groups (according to the World Reference Base for Soil Resources, 2006) on four test plots with the use of the high-resolution (Landsat and QuickBird) satellite imagery, original field data on more than 200 soil profiles, and literature data included in the soil database. Three test plots belonged to the ecotone between tundra and forest-tundra zones, and the fourth plot characterized the middle taiga zone. Spatial distribution patterns of soil carbon in different soil subgroups and genetic horizons were characterized for the areas with the mosaic soil and vegetation covers. The mean soil carbon content for the first three test plots in permafrost area was estimated at 39.5 kg C/m², including 28.7 kg C/m² in the upper soil meter. The mean soil carbon pool of the taiga plot reached 16.7 kg C/m² (0–100 cm).     

Grazing intensity in subarctic tundra affects the temperature adaptation of soil microbial communities

Grazing by large ungulates, such as reindeer (Rangifer tarandus L.), in subarctic tundra exerts a considerable effect on the soil microclimate. Because of higher insulation by the aboveground vegetation in light versus heavily grazed areas, soil temperatures during the growing season are considerably higher under heavy grazing. Here, we hypothesized that these grazer-induced changes in soil microclimate affect the temperature sensitivity of soil microbial activity. To test this hypothesis, we conducted soil incubations at different temperatures (4 °C, 9 °C and 14 °C) for six weeks using soils from sites with contrasting long-term grazing intensities. Microbial respiration at low temperature (4 °C) was significantly higher in soils under light grazing than in soils under heavy grazing; however, grazing intensity did not affect respiration rates at 9 °C and 14 °C. In soils under light grazing, post-incubation β-glucosidase (BG) activity at 4 °C was higher in soils that had been incubated at 4 °C than in soils incubated at 14 °C, suggesting functional adaptation of the soil microbial community to low temperature. Similar adaptation was not detected in soils under heavy grazing. Ion Torrent sequencing of bacterial 16S rRNA genes showed major differences in the bacterial community composition in soils incubated at different temperatures. Overall, our results indicate that tundra soil microorganisms may be more cold-adapted under low than high grazing intensity. Due to this difference in temperature adaptation, the consequences of climate warming on soil microbial processes may be dependent on the grazing intensity.     

Temperature response of soil organic matter mineralisation in arctic soil profiles

Soil organic matter (SOM) in arctic and boreal soils is the largest terrestrial reservoir of carbon. Increased SOM mineralisation under increased temperature has the potential to induce a massive release of CO₂. Precise parameterisation of the response of arctic soils to increased temperatures is therefore crucial for correctly simulating our future climate. Here, we investigated the temperature response of SOM mineralisation in eight arctic soil profiles of Norway, Svalbard and Russia. Samples were collected at two depths from both mineral and organic soils, which were affected or not by permafrost and were incubated for 91 days at 4, 8, 12, and 16 °C. Temperature response was investigated through two parameters derived from a simple exponential model: the intensity of mineralisation, α, and the temperature sensitivity, Q10. For each sample, SOM quality was investigated by ¹³C-NMR, whereas bacterial and fungal community structure was characterised by T-RFLP and ARISA fingerprints, respectively. When estimated from the whole incubation period, α proved to be higher in deep permafrost samples than in shallow active layer ones due to the presence transient flushes of mineralisation in deep permafrost affected soils. At the end of the incubation period, after mineralization flushes had passed, neither α nor Q10 (averaging 1.28 ± 0.07) seemed to be affected by soil type (organic vs mineral soil), site, depth or permafrost. SOM composition and microbial community structure on the contrary where affected by site and soil type. Our results suggest that deep samples of permafrost affected soil contain a small pool of fast cycling carbon, which is quickly depleted after thawing. Once the mineralization flush had passed, the temperature response of permafrost affected soil proved to be relatively homogenous among sample types, suggesting that the use of a single temperature sensitivity parameter in land surface models for SOM decomposition in permafrost-affected soils is justified.     

Influence of land use changes on the soil temperature regime of Andosols on Tenerife, Canary Islands, Spain

Soil temperature influences both soil formation processes and land use possibilities, and is a classification criterion in some systems. Vegetation cover is one of the factors that affects temperature. In this paper, we estimate the classes of soil temperature regimes, using Soil Taxonomy, for Andosols located in parts of the island of Tenerife, Canary Islands, Spain, which are influenced by the trade winds. The study focuses on soils under three types of natural vegetation – cloud forest, tree‐heath woodland and pine forest – and adjacent plots where the vegetation has been replaced with, respectively, pine forest, herbaceous plants and cropping, and herbaceous plants. Temperature was measured monthly at 50‐cm depth for a period of 2–4 years at three sites, both in the natural vegetation plots and in the plots where the vegetation was modified. Under natural vegetation the soil temperature regimes are all ‘iso’ (difference < 6°C between summer and winter temperatures) and reflect tropical conditions. The switch to shorter vegetation, and particularly to use of the land for cropping, causes the soil temperature regime to change from iso to non‐iso.     

CO2 and N2O emissions from gleyic soils in the Russian tundra and a German forest during freeze-thaw periods—a microcosm study

Knowledge is scarce on mineralization of soil organic carbon (SOC) in and N₂O emissions from tundra soils in periods of alternate freezing and thawing. Our objectives were to study the CO₂ and N₂O emissions from two silty gleyic soils formed in different climate zones (a gleyic Cryosol located in the Russian tundra, and a stagnic Gleysol located in an oak stand in central Germany) during freeze-thaw events. Soils were adjusted to a matric potential of −0.2 kPa and emissions were measured in 3-h intervals during an incubation period of 50 days including three freeze-thaw cycles. CO₂ emissions from the German oak forest soil were twofold higher than those of the tundra soil. The ratios of the mean CO₂ production rate before the freezing to the mean CO₂ production rate after thawing ranged from 0.63 to 0.73 for the forest soil and from 0.85 to 0.89 for the tundra soil. The specific CO₂-C production rate (CO₂-C/SOC) was 0.16 for the tundra soil and 0.57 for the forest soil. The results indicate that bioavailability of SOC was markedly smaller in the tundra soil than in the forest soil. Large N₂O emissions were found for the German forest soil, but no N₂O emissions were observed for the tundra soil. The main reason for the absence of N₂O emissions was most likely the negligible availability of nitrate for denitrification. There was some indication that the initial increase in mineralization of SOC induced by freezing and thawing differs between soils from various climatic regions, probably mainly due to a differing bioavailability of the SOC and differing releases of nutrients after thawing.     

Particle-size distribution in soils of West Antarctica

The particle-size distribution in soils sampled near Russian polar stations in West Antarctica has been studied. It is shown that the soils of the Subantarctic zone (the Bellingshausen Station on King George Island) are characterized by a higher content of silt and clay in the fine earth fraction and by a higher content of the fine earth fraction in comparison with the soils of the proper Antarctic tundra barrens near the Lenin-gradskaya Station and the Antarctic cold desert near the Russkaya Station. In the latter soils, the content of rock fragments is higher than that in the soils of the Antarctic tundra barrens. In the soils of the tundra barrens, a considerable accumulation of fine earth may take place in large cavities (hollows) on the stony bedrock surface. Desert pavements are formed in both types of Antarctic landscapes.     

Morphology and properties of the soils of permafrost peatlands in the southeast of the Bol’shezemel’skaya tundra

The morphology and properties of the soils of permafrost peatlands in the southeast of the Bol’shezemel’skaya tundra are characterized. The soils developing in the areas of barren peat circles differ from oligotrophic permafrost-affected peat soils (Cryic Histosols) of vegetated peat mounds in a number of morphological and physicochemical parameters. The soils of barren circles are characterized by the wellstructured surface horizons, relatively low exchangeable acidity, and higher rates of decomposition and humification of organic matter. It is shown that the development of barren peat circles on tops of peat mounds is favored by the activation of erosional and cryogenic processes in the topsoil. The role of winter wind erosion in the destruction of the upper peat and litter horizons is demonstrated. A comparative analysis of the temperature regime of soils of vegetated peat mounds and barren peat circles is presented. The soil–geocryological complex of peat mounds is a system consisting of three major layers: seasonally thawing layer–upper permafrost–underlying permafrost. The upper permafrost horizons of peat mounds at the depth of 50–90 cm are morphologically similar to the underlying permafrost. However, these layers differ in their physicochemical properties, especially in the composition and properties of their organic matter.