Modeling of the thermal influence of fires on the physicochemical properties and microbial activity of litter in cryogenic soils

Periodic surface fires in the cryolithozone (the northern taiga subzone) are the main factor determining the qualitative and quantitative characteristics of the soil organic matter. The specific features of the changes in the physicochemical parameters and microbial activity of the organic horizons in the cryogenic soils under larch forests of the northern taiga after the impact of high temperatures were revealed. The temperatures of fires of different intensity were simulated in laboratory conditions. The thermal impact on the litter organic matter during the surface fires may increase the CO₂ emission from the surface of the soil in the postfire communities due to the destruction of organic compounds only for a short time. After fires of high intensity with strong mineralization of the litters, during a period of more than 1 month, the pyrogenic effect on the organic horizons of the soils under the larch forests of the cryolithozone determined the reduction of the CO₂ emissions in the freshly burned areas as compared to the intact stands.     

Characteristics of Clay Minerals in Podzols and Podzolic Soils

The clay minerals in Podzols and podzolic soils developed under coniferous forests in the Subarctic and Cool-temperate zones are characterized by the predominance of smectite and/or mica-smectite interstratified minerals in the eluvial horizons and chlorite-vermiculite intergrade in the illuvial horizons. A large amount of vermiculite is present in the eluvial horizons of some podzolic soils in the Cool-temperate zone. The illuvial horizons of these soils also contain free iron oxides such as goethite. Imogolite and allophane are present in the illuvial horizons of several soils derived from volcanic ashes. It is suggested that the critical bioclimate for the release of interlayered aluminum from the 2:1-type minerals lies between the Cool- and Warm-temperate zone. In the eluvial horizons of Podzols and podzolic soils, mica minerals and chlorite, as primary minerals, have been transformed to smectite through the pedogenic process. Based on previous studies on the structure and degradation of the dioctahedral mica minerals, it is considered that smectite is transformed from 1M-type mica minerals directly, and from 2M-type mica minerals via mica-smectite interstratifled minerals. The formation of a smectite lattice in the eluvial horizon should be a clay-mineralogical indicator of podzolization.     

Soils of postpyrogenic larch stands in Central Siberia: Morphology,physicochemical properties,and specificity of soil organic matter

Morphological features, physicochemical properties, and specific characteristics of the organic matter of cryozems (Cryosols) under postpyrogenic larch forests affected by fires 2, 6, 22, 55, and 116 years ago are considered. The morphological changes in the soils affected by fires are manifested by the burning of the upper organic horizons with preservation of pyrogenic features in the soils for more than a century after the fire. In the first years (2 and 6 years) after the fire, the acidity of the organic horizons and their base saturation become lower. The postpyrogenic soils are characterized by the smaller contribution of the organic horizons to the total pools of soil organic carbon. In the studied cryozems, the organic carbon content is correlated with the contents of oxalate-extractable iron and aluminum. A decrease in the content of water-soluble organic compounds in the soils is observed after the fires; gradually, their content increases upon restoration of the ground cover.     

Soil horizons as the basis for classification of alluvial soils

The horizons of different types in alluvial soils of central Russia are compared with respect to their morphological characteristics using the method of dendrograms. It is argued that diagnostic soil horizons should clearly reflect in their properties the character of pedogenic processes and, thus, be the basis for classification of alluvial soils. Overall, seven types of soil horizons are suggested as diagnostic horizons for flood-plain soils of the Russian Plain.     

Soils of Mountainous Forests and Their Transformation under the Impact of Fires in Baikal Region

Data on postpyrogenic dynamics of soils under mountainous taiga cedar (Pinus sibirica) and pine (Pinus sylvestris) forests and subtaiga–forest-steppe pine (Pinus sylvestris) forests in the Baikal region are analyzed. Ground litter–humus fires predominating in this region transform the upper diagnostic organic soil horizons and lead to the formation of new pyrogenic organic horizons (Opir). Adverse effects of ground fires on the stock, fractional composition, and water-physical properties of forest litters are shown. Some quantitative parameters of the liquid and solid surface runoff in burnt areas related to the slope gradient, fire intensity, and the time passed after the fire are presented. Pyrogenic destruction of forest ecosystems inevitably induces the degradation of mountainous soils, whose restoration after fires takes tens of years. The products of soil erosion from the burnt out areas complicate the current situation with the pollution of coastal waters of Lake Baikal.     

长白山北坡原始林采伐对土壤性质影响的研究

长白山北坡是我国中纬度地区保持得比较完好的著名原始林区。林木组成复杂,成林树种丰富,每公顷蓄积量可达300—600立方米。而适合采伐的成过熟林已占绝大部分。据白河林业局资料:其林分蓄积中成过熟林占90.1%,这些成过熟林的林木生长量已大为减退,平均生长率为3.96%,而自然枯损率却占1.87%。特别是针叶树种平均自然枯损率高达3.79%,几乎与平均生长率相等¹⁾,这表明该局的森林资源应及时开发利用。另一方面,这些可采伐的原始林,地处熔岩高原,是第二松花江的源头,现有森林覆被对于调节气候、涵养水源、保持水土的作用是难于估量的。若采伐方式不当,是否会引起森林立地条件恶化而不利于更新造林,导致生态失去平衡并带来极大的灾难。为此,1982年吉林省林学会联合我院等十多个单位,针对上述问题,从各方面进行考察。笔者等用设立标准地调查对比的方法,于落叶松纯林和阔叶红松林采伐迹地上进行研究,现将初步结果报道如下。     

Postpyrogenic transformation of soils under Pinus sibirica forests in the southern Lake Baikal basin

The results of experimental investigations of the postpyrogenic dynamics of the widespread rawhumus podzols under Pinus sibirica forests in the southern Lake Baikal basin are discussed. Ground fires transform the diagnostic surface organic soil horizons into organic pyrogenic horizons (Opir, OL/Opir, and AOpir). The adverse effect of ground fires of different intensities on the changes in the reserves, the fractional composition of the litters, and the chemical composition of the organic horizons is shown. The soils of dark coniferous forests are inclined to long-lasting restoration. The Pinus sibirica regrowth under the canopy of deciduous species serves as the basis for the restoration of native stands and the formation of the soils characteristic of the southern part of the Lake Baikal basin.     

Effects of Exotic Plant Species on Soil Properties in Hardwood Forests of New Jersey

Two exotic plant species, Berberis thunbergii and Microstegium vimineum, recently have invaded deciduous hardwood forests in the Northeast. We examined changes in soil properties that may be associated with this invasion in three parks in northern New Jersey. In each park, we collected soil and vegetation data along transects that were established across heavily infested areas and extended into uninvaded forest. The data were analyzed statistically by ANOVA and Canonical Correspondence Analysis (CCA). Significant differences were found between invaded and uninvaded plots in both soil and vegetation characteristics. Invaded areas have fewer oaks (Quercus spp.) in the canopy, and lack the native understory shrubs (Vaccinium spp.). The pH of soils in the invaded areas is significantly higher than in the uninvaded areas, and the litter and organic horizons are thinner. The data cannot show that the exotic species have caused these changes. However, the occurrence of contrasting soils in adjacent areas of native vegetation, with no evidence of differences in land-use history between areas, suggests that such a cause-and-effect relationship exists. We propose a feedback loop involving the exotic plants, and the presence of earthworms to explain these dramatic soil differences.     

The genesis of vertisols with gilgai microtopography: A review

Different hypotheses about the genesis of gilgai microtopography and corresponding soil complexes with clayey swelling soils are considered in this review. Their diversity is stipulated by specificities of the objects themselves and by the history of studies of the composition, properties, regimes, and landscape conditions of the areas with Vertisols in different countries. Most of the hypotheses about the genesis of Vertisols with the gilgai microtopography suggest that strong swelling–shrinking processes take place in these soils in the course of moistening–drying cycles; the origin of shear stress in the soils, its spatial patterns, and the particular ways of translocation of the soil material are discussed. At the early stage of Vertisol studies, a hypothesis about the leading role of the process of “self-swallowing” of the soils as a result of filling of open cracks with the material from the upper soil horizons was popular. However, numerous facts suggest that the intensity of this process is relatively low, so that it cannot play the major role in the gilgai formation and cyclic changes in the thickness and properties of the soil horizons in Vertisols. Another important mechanism is the uneven moistening and drying of the whole soil volume resulting in the irregular distribution of inner tensions in the soil with the development of shear stress and plastic deformation of the soil mass. The hypotheses suggested in the recent decades are based on the models of soil mechanics. A number of hypotheses consider possible alternation and duration of evolutionary stages of the development of Vertisols with the gilgai microtopography.     

Transformation of peat horizon in swampy southern taiga forests under the impact of surface drainage

The results of stationary studies of swampy southern taiga forests in Yaroslavl oblast are presented. Estimates of changes in the thickness of peat horizon in peat podzolic gley soils (Folic Albeluvisols) of forests subjected to clearcutting and further intensive forest management in the past 30 years are given. The mean annual precipitation in these three decades has been 116 mm higher than that during the preceding three decades, which has led to a progressive swamping of spruce stands on heavy loamy soils within virtually flat (with slopes up to 0.0035) surfaces and an increase in the organic matter storage in the peat soil horizon with the mean annual rate of 22–68 g/m². On more pronounced slopes (0.0050), no swamping of spruce and pine stands growing on sandy soils has taken place. Surface drainage of swampy forests through the network of shallow ditches has led to an increase in the productivity of forests; in most cases, the pool of organic matter in the peat horizon has been decreasing with the mean annual rate of 32–46 g/m². This attests to the reversible character of swamping in dependence on climatic fluctuations and forestry measures. Changes in the carbon pool of swampy soils during short (several years) excessively wet or excessively dry periods may be significantly higher than the average values for 30 years in different types of forests. This allows us to consider swampy forests as the source of significant errors in the estimates of the current contribution of biota to the carbon cycle, because their role (as well as the role of other forests) is assessed without taking into account considerable short-term fluctuations in the carbon pool of their soils.     

Microstructure of genetic horizons in automorphic soils of the Timan Ridge

Data are presented on the physicochemical composition and specific macro-, meso- and micro-morphological features of automorphic soils formed on silty loams in the northern and middle taiga subzones of the Timan Ridge. These soils have a texture-differentiated profile and are well aggregated, which is manifested at all levels of structural organization of the soil mass. The morphological structure of the middle soil horizons is characterized by the presence of specific nongleyed cryometamorphic horizon CRM. Its formation is due to the development of long-term seasonal cryogenic processes in relatively deep (up to 40 cm) light and medium loam deposits under conditions of the northern and middle taiga subzones. The processes of cryometamorphism, combined with Al-Fe-humus and textural differentiation, result in the formation of podzolic, iron-illuvial, cryometamorphic, and textural horizons (O-E-BF-CRM-BT). The textural horizons have a set of micromorphological features indicating that recent clay illuviation is a weak process.     

The humus status of modern and buried volcanic soils in Mexico and its role in the paleogeographic interpretation of tephra-paleosol sequences

Chemical and optical characteristics of soil humus have been analyzed as “memory” components of the Pleistocene volcanic paleosols in Mexico. We have studied the A1 horizons of buried Andosols of the Nevado de Toluca series and of the modern Andosols formed under different bioclimatic conditions. Data on the organic matter of buried paleosols suggest that Andosols of the Nevado de Toluca series were formed in humid forest ecosystems. Optical characteristics of the humic acids and data on the molecular-mass distribution of the humus make it possible to assume that these soils were formed under pine forests rather than under fir forests.     

Soil cover pattern on the northern macroslope of the Tsagan-Daban Ridge in the Transbaikal region

Regularities of soil distribution in the basin of the Vorovka River on the northern macroslope of the Tsagan-Daban Ridge are discussed, and the grouping of soil cover patterns in this area is suggested. Dissected middle-mountain areas covered by taiga forests are characterized by a combination of predominate soddy podburs with small homogeneous areas of podburs and lithozems. Within the piedmont part of the basin, components of soil combinations are different. The major areas are occupied by sandy soils under dry grassy pine forests; poorly developed soils are formed on recent alluvial and colluvial deposits in the depressions and hollows.     

Population and biomass of soil microorganisms in old-growth primary spruce forests in the Northern Taiga

The number and biomass of microorganisms in the soils under lichen, grass-bilberry, and grass spruce forests of old age were studied on the Kola Peninsula. The dry biomass of microorganisms in the organic soil horizons was shown to reach 28 mg/g with a predominance (96 to 99%) of micromycetes. At tree trunk sites, in the organic horizons of all the soils studied, where the contents of organic carbon and mineral nutrients were higher, the number and biomass of all the groups of microorganisms was lower than in those in the soils of the gaps. The factors limiting the functioning of microorganisms in the soils under spruce tree crowns are thought to be the high acidity of the water flowing down the tree trunks and the high phenol content in it. In the mineral horizons of the soils, the patterns of the microorganisms were opposite: in all the spruce forests, the fungal biomass was the highest in the soils of the trunk zones, as well as the bacterial population and biomass in the grass spruce forest. In the latter, the maximal length of the actinomycete mycelium was also recorded in the soil of the trunk zones with the elevated contents of carbon and mineral nutrients.     

THE PEDOGENESIS OF SOME GIBBSITIC SOILS FROM THE SOUTHERN UPLANDS OF SCOTLAND

The mineralogy of ten profiles developed from hornfelsic rocks on the summit areas of the Merrick and Kells Hills has been investigated by X-ray powder diffraction, thermal, infra-red, and optical methods. The soil clays of the C horizons of all profiles contain 6 to 37 per cent of gibbsite but this mineral is not found in the A horizons. Optical observations reveal that gibbsite is associated with hematitic rock fragments which are considered to represent older soil material–i.e. are pedorelicts. It is suggested that the Merrick soils are polygenetic and consist of two soil stratigraphic units, recent pedogenic effects being superimposed on a basal horizon that has been strongly influenced by preglacial or interglacial weathering.     

Morphometric profiles of pore space in loamy soils of the forest and steppe zones of European Russia

A computer-based image analysis of vertically oriented thin sections was applied to study changes in the shape and orientation of fine soil macropores (d = 0.2−2.0 mm) in the profiles of soddy-podzolic soils and typical (migrational-mycelial) chernozems. Generalization of the obtained morphometric data was based on the theory of mereology, a scientific discipline studying the structure (part-whole relationships) of classified objects. As a first approximation, generalized data characterized archetypes of morphometric porespace profiles of the studied soils. The archetype of the pore-space profile of the soddy-podzolic soil consists of four components (meronyms) corresponding to the humus-accumulative, eluvial, textural (clay-illuvial), and transitional to the parent material (BC) horizons. Sharp boundaries between the upper horizons specify sharp changes in the studied meronomic indices of the shape and orientation of soil pores. The pore-space profile of the migrational-mycelial chernozem consists of two major components: specific pores in the granular dark-humus (AU) horizon and complex pore space of the BCA and BCca horizons that are poorly differentiated with respect to the shape and orientation of their fine macropores despite clear genetic differences between these horizons. Pore-space patterns in the lower (transitional to the parent material) horizons of the studied soils are characterized by the high degree of similarity (>75%). Pore-space patterns in the upper horizons of the studied soils are different; the level of their similarity does not exceed 24–41.5%. The results obtained in this study hold promise in the use of morphometric characteristics of the pore space in separate genetic soil horizons as meronyms composing archetypes of the pore-space profiles of different soils. Such archetypes may be used for diagnostic purposes as reference pore-space profiles of the particular types of soils.     

Chemical time bombs related to forestry practice: Distribution and behaviour of pollutants in forest soils

Heavy metals and persistent organic pollutants from atmospheric deposition and from fertilizer and pesticide applications are important hazardous substances in forest soils. Data are presented showing that these substances preferentially accumulate in the upper humic horizons of the soils. Another group of substances to be considered in relation to the chemical time bomb concept are the components of humus and soil minerals, mainly nitrogen and metals, which May, be mobilized and thus threaten groundwater quality. Forestry management practices such as thinning, cropping, fertilization and liming are discussed as potential triggers for the mobilization of harmful substances. in this context, The turnover (build-up and mineralization) of organic matter plays a crucial part. It will be shown, however, that even more danger arises from soil acidification induced by the atmospheric deposition of acidifying pollutants such as sulphates and nitrates.     

Humus Horizons of Soils in Urban Ecosystems

The origin, structure, composition, and properties of soil humus horizons in functional zones of St. Petersburg have been studied. The radiocarbon age of organic matter in the humus horizons varies from 500 to 2700 years, which attests to the natural origin of humus. The structure of microbiomes in the humus horizons of soils under different plant communities has its specific features. The taxonomic structure of microbial communities at the phylum level reflects both genetic features of natural soils and the impact of anthropogenic factors, including alkalization typical of the studied urban soils. Tomographic studies have shown that the transporting system of humus horizons is less developed in the anthropogenically transformed soils in comparison with the natural soils. It can be supposed that the intensity of water and gas exchange in the anthropogenic soils is much lower than that in the natural soils. The fractional and group composition of humus in the urban soils is specified by the long-term pedogenesis, on one hand, and by the impact of metabolic products of the city and the factors of soil formation in the megalopolis, on the other hand. Bulk density of the humus horizon in the urban soils is higher than that in the natural soils; the portion of overcompacted humus horizons in the urban soils reaches 44%. Humus horizons of the lawns along highways are most contaminated with heavy metals: Pb, Zn, and Cu. There are no definite regularities in the distribution of major nutrients (NPK) in the humus horizons of anthropogenic soils.     

Population and biomass of microorganisms in soils of pyrogenic succession in the northern taiga pine forests

In the organic horizons of the Al-Fe-humus podzols under the old pine forests of the northern taiga, the biomass of all the groups of microorganisms, the length of the fungal and actinomycete mycelium, the number of fungal spores, and the bacterial population were maximal (13 mg/g) irrespectively of the stage of pyrogenic succession. The share of fungi (mainly, of basidiomycetes) exceeded 90%. In the mineral root-inhabited soil horizons, the biomass of microorganisms was not greater than 1.0 mg/g. The soil under the lichen pine forest had the smallest biomass of microorganisms as compared to the soil under the pine forests that were not exposed to fire for a long time. At all the stages of the pyrogenic succession, the most favorable conditions for the functioning of microorganisms were in the root-inhabited horizons of the soils in near-stem sites due to the accumulation of nutrients there. In the soils of these zones, the basidiomycete biomass was greater than that in the soils of the gaps. In the mineral soil horizons, buckleless micromycetes demonstrated the same trend. No distinct parcella differences, with respect to the soil nutrient regime, were found only for the prokaryotes. The fungi in the Al-Fe-humus podzols may be used as indicators for the pyrogenic succession stages of forest ecosystems. At the early stages, micromycetes without buckles prevailed, and, in the course of succession, the share of basidiomycetes clearly increased. The density and structure of mycorrhiza were tightly related to the nutrient regime of the soils. The increase in the concentration of available biogenic elements in the root-inhabited soil horizons did not cause the necessity of developing complex mycorrhiza forms.     

Specific features of the development of soils of hydromorphic ecosystems in the northern taiga of Western Siberia under conditions of cryogenesis

Differently directed and heterochronous cryogenic processes have contributed to the contrasting soil cover patterns and spatial heterogeneity of the properties of soils in hydromorphic ecosystems of the discontinuous permafrost zone of the northern taiga in Western Siberia. Frost heave and permafrost thawing within ecosystems of highmoor bogs have led to the development of specific cryogenic landforms, such as flat-topped and large peat mounds. A set of cryogenic soils is developed in these ecosystems; it includes different variants of cryozems, gleyzems (Cryosols), and peat soils (Histosols). The distribution of these soil types is controlled by the local topography and thawing depth, other factors being insignificant. Alternation of peat horizons of different types and ages, whirl-like patterns of horizon boundaries, considerable variations in the thickness of soil horizons, and inversions of soil horizons under the impact of frost cracking, frost heave, and cryoturbation are typical of the considered soils. Thawing depth is the most significant factor affecting the thickness of organic horizons, the soil pH, and the degree of decomposition of peat. As a result of the upward movement of bog ecosystems under the impact of frost heave, peat soils are subjected to considerable transformation: peat horizons undergo mineralization, and the thickness of organic horizons decreases; in some cases, eluvial–illuvial differentiation of the mineral horizons takes place, and peat podzols are developed. However, the opposite process of the return of the soils to the bog stage of pedogenesis with peat accumulation may take place in any time in the case of activation of thermokarst processes.