Diagnostic parameters of soil formation in gray forest soils of abandoned fields overgrowing with pine forests in the middle reaches of the Angara River

The content, differentiation in the profile, and dynamics of the mobile iron compounds can serve as adequate diagnostic parameters of the direction of the pedogenesis upon the overgrowing of abandoned fields with pine forests in the middle reaches of the Angara River Region in the area affected by the Bratsk water reservoir. The bulk chemical composition of the soil remains relatively stable in the entire profile against the background of the eluvial-illuvial redistribution of the finest particle-size fractions and mobile iron compounds under the impact of the long-term seasonal freezing, the percolative soil water regime, and the alternating redox conditions. The development of accumulative processes in the soil is accompanied by the weak manifestation of eluvial and pulsating gley processes as the initial stages of podzolization under the influence of the growing pine forests.     

The influence of pine forests of different ages on the biological activity of layland soils in the middle Angara River basin

The influence of pine forests of different ages (from 25 to 85 years) restoring on old plow land soils is reflected in the biological processes proceeding in them. The drastic decrease in the absolute and relative number of actinomycetes, along with an increase of the fungal population in the microbial complexes of the soils (within the whole profiles), indicates that the microbocenoses acquire “forest” properties. In the soils under the younger pine forests, the processes of microbiological mineralization and specific respiration activity are more active than in the soils under the older pine forests. With the age of the pine forests, the soil profiles become more differentiated according to the eluvial-illuvial type.     

Post-fire transformation of the microbial complexes in soils of larch forests in the lower Angara River region

The postfire transformation of the functional activity of the microbial cenoses and the main soil properties under mixed larch forests were studied in the lower reaches of the Angara River. It was shown that the intensity of the postfire changes in the population density, biomass, and activity of the microorganisms in the dark podzolized brown forest soil depended on the degree of burning of the ground cover and the surface litter during the fire. The maximum effects of the fire on the microbial cenoses were observed in the litter and the upper 5-cm-thick layer of the dark-humus horizon in the areas of intense burning. The postfire restoration of the structural-functional activity of the microbial cenoses was determined by the degree of transformation of soil properties and by the postpyrogenic succession in the ground cover. The microbial complexes of the dark podzolized brown forest soils under mixed larch forests in the studied region restored their functional activity after the fires of different intensities quicker than the microbial cenoses of the sandy podzols in the pyrogenic lichen-green-moss pine forests of the same zone.     

Transformation of forest litter properties under controlled burning of fir forests defoliated by Siberian moths in the Lower Angara River basin

The results of studying the dynamics of forest litter properties in the loci of a Siberian moth (Dendrolimus sibiricus) mass outbreak are considered. As a fir forest defoliated by this pest burns, the reserves and fractional composition of the forest litter, its actual acidity, and its chemical composition drastically change. Upon the burning out of such forests, the litter complex of invertebrates is fully destroyed and begins restoring only two years after the fire.     

Microbiological diagnostics of the status of pyrogenically changed pine forests in the Lower Angara River basin

The structure and functions of the microbial complexes in the soils after surface fires of different intensity were studied. The fires of high and medium intensity were found to lead to a significant decrease in the number and functional activity of microorganisms participating in the nitrogen-carbon cycle. The degree of changes in the postfire status of the soil microbocenoses was revealed to be related to the joint action of pyrogenesis and the hydrothermal conditions at the moment of the fire rather than to the fire intensity. The favorable combination of the elevated soil moisture and soil heating stimulates the microbiological processes of organic matter mineralization, thus, improving the forest-growing conditions for the pine forests. The microbial biomass, basal respiration, and the microbial metabolic coefficient are shown to adequately reflect the postfire status of the microbial complexes.     

Transformation of microbial cenoses in soils of light coniferous forests caused by cuttings and fires in the Lower Angara River basin

The influence of surface fires and cutting on the quantitative and functional parameters of microbial cenoses in the soils of light coniferous forests in the Lower Angara River basin was studied. In the litters of soddy-podzolic soils under pine forests, the microbial biomass was 4080–4700 μg C/g; the basal respiration was 17.00–20.32 μg C-CO₂/g/h; and the qCO₂, 4.17–4.33 μg C-CO₂/mg C_mic/h. In the humus-accumulative horizon, these values were 880–1160 μg C/g, 2.48–4.12 μg C-CO₂/g/h, and 2.83–3.55 C-CO₂/mg C_mic/h, respectively. In the litter of the one-year-old felled area, the content of microbial biomass carbon was by two times lower; in the litter of burned plots, it was by 60–70% lower than in the litter of the control area. The intensity of the microbial respiration did not change proportionally to the microbial biomass content, which resulted in an imbalance between the processes of the organic matter mineralization-immobilization towards a release of CO₂ as evidenced by the increase of the qCO₂ values by 2–4 times. In the five-year-old felled area, at the stage of restoring the herbaceous vegetation, a tendency towards the stabilization of the destructive microbiological processes was revealed. In the felled areas, the high number of heterotrophic microorganisms, the reduced oligotrophy of the soil organic horizons, and the more intense microbiological mineralization of the organic matter were observed. The surface fires in the felled areas and forests significantly affected the structure and the number of ecological-trophic groups of microorganisms in the litters, the humus-accumulative horizons, and in the upper mineral soil layers. The maximal structural and functional disturbance in the soil microbial complex was found in the logged areas affected by fires.     

Transformation of organic matter and clay minerals in cultivated gray forest soils

Mechanisms of the agropedogenic transformation of cultivated gray forest soils are discussed. It is shown that the loss of organic carbon from these soils upon their cultivation is mainly due to the intense mineralization of an easily decomposable fraction having a density of less than 2 g/cm³ and a characteristic size above 50 μm. Simultaneously, a certain portion of soil microaggregates is destroyed. Several additional indices of the processes of soil erosion and sediment accumulation on the soil surface (soil aggradation) are suggested. These indices take into account the character of soil clay minerals and soil organic matter. Indicative characteristics of the second humus horizon are suggested on the basis of published materials and new analytical data.     

Carbon budget in agroecosystems on gray forest soils in the Lake Baikal region

The carbon budget in agroecosystems with spring wheat was studied in long-term (1997–2004) field experiments on gray forest soils in the forest-steppe of the Lake Baikal region, including soils polluted with the fluorides emitted by an aluminum plant. Pollution was revealed to increase the deficit in the carbon budget due to the more intense mineralization of organic matter and CO₂ emission from the soils. Raising of the crops’ productivity upon permanent application of fertilizers may provide maintenance of a positive carbon budget.     

Quantitative approach to classification of gray forest soils in the Volga-Kama forest-steppe region

On the basis of factual data obtained by the Soil Science Department of the Privolzhskii Federal University and available from literary, virtual reference “images” of gray forest soils as distinguished in classification systems of 1977 and 2004 have been obtained with the use of the methods of multivariate statistics for the Volga-Kama forest-steppe region. Discriminant functions and have been obtained, and classification functions have been developed with the help of numerical methods to diagnose new representatives of gray forest soils. The virtual “images” of the soils can be used for the improvement of soil systematization and for solving various applied problems of land use.     

Nitrogen budget in agroecosystems on gray forest soils under long-term fertilization

Long-term stationary field experiments were performed to study the efficiency of increased rates of nitrogen fertilizer in crop rotations with cereal crops, perennial grasses, clover, and plow fallow on gray forest soils. It was found that an excess of mineral nitrogen (mainly of nitrates) accumulated in the soil in the case of unbalanced nitrogen fertilization and long-term fallowing creates conditions for the development of unfavorable processes in the nitrogen cycle. Significantly increasing nitrogen losses from the agroecosystem because of leaching and denitrification constitute a depletion hazard for the soil nitrogen pool.     

Carbon budget in arable gray forest soils under different land use conditions

The effect of different land-use practices on the carbon budget in old arable gray forest soils of Russia was studied in field experiments. A short-term (for 6–7 years) cessation of mineral fertilization had no negative effects on the carbon budget in the agrocenoses studied. Only the combination of zero fertilization with the return to monoculture and the introduction of black fallows created a negative budget of humus in the soil. The regrassing of the eroded arable soil for 24 years increased the humus reserve in the 0- to 60-cm layer by a factor of 1.6–1.7. The average annual accumulation of carbon and nitrogen after the restoration of the perennial vegetation was 106–128 g C/m² and 11–16 g N/m², respectively.     

The influence of tree species on the biomass of denitrifying bacteria in gray forest soils

The biomass of two groups of microorganisms was studied in gray forest soils under six tree species (spruce, Scotch pine, Arolla pine, larch, birch, and aspen) and in the soil of a layland (a clearing in the forest) using kinetic methods. The biomass was the highest in the soil of the layland. The lowest (19.4 μg C/g of soil) biomass of heterotrophic microorganisms was found in the soil under the birch trees, and the highest one (41.7 and 32.0 μg C/g), under the pine and spruce ones. The biomass of denitrifying microorganisms was lower by thirty times than that of the heterotrophic ones. In the soils under the pine and spruce trees (8.4 and 9.2 μg C/g, respectively), the biomass of the denitrifying microorganisms was the lowest; under the birch and larch trees, it was the highest (16.7 and 13.7 μg C/g).     

Iron compounds in sulfate-carbonate soils on red-colored Cambrian rocks in the southern Angara region

In some regions of Irkutsk oblast in the southern Angara region, brown carbonate-sulfate soils have been formed on red-colored Cambrian rocks. In the automorphic soils, even a low content of hematite strongly affects the soil color, and the increase in its content only slightly enhances the red color of the soil. The brown color of carbonate soil is due to the partial preservation of lithogenic hematite in the upper part of the soil profile. The abundant gypsum “preserves” the lithogenic hematite in the carbonate-sulfate soil; the oxidation of iron is also hampered in this soil. Important changes occur in the wetted dark solonchak: lithogenic hematite is dissolved, the structure of iron chlorite loses order, and coarse and crystallized magnetite is formed in the humus horizon.     

Post-pyrogenic changes in the hydrothermal parameters of soils in middle-taiga pine forests

Results of long-term studies in middle-taiga pine forests on sandy podzols after controlled surface fires are presented. The changes in the soil hydrothermal conditions caused by the pyrogenic transformation of the soil and the pyrogenic and postpyrogenic changes in other components of the forest biogeocenoses were revealed. Along with the general character of the changes in the soils’ hydrothermal conditions, some differences in the degree of their manifestation between different regions due to the different fire intensities were revealed. It was concluded that the pyrogenic impact disturbed the existing material and energy exchange between the atmosphere and the soil, which is the main process of soil formation and development. Consequently, forest fires are a powerful and active factor of recent pedogenesis.     

Changes in the properties of cultivated gray forest soils after their abandoning

Changes in the physical, physicochemical, and biological properties of cultivated gray forest soils after their abandoning and overgrowing with meadow and forest vegetation for 8–10 years are clearly seen in the upper part of the former plow layer. The organic matter content and the content of available forms of phosphorus and potassium increase; a significant increase in the root biomass and in the soil biological activity is observed. Changes in the physical properties—an increase in the degree of soil aggregation and a decrease in the bulk density values—are seen in the upper and middle parts of the former plow layer. The biological factor is the major factor of transformation of formerly cultivated gray forest soils upon their abandoning and overgrowing with meadow and forest vegetation. At the same time, a significant role in the improvement of the structural state of the soils belongs to the physical shrink-swell and freezing-thawing processes.     

Transformation of gray forest soils upon technogenic salinization and alkalization and subsequent rehabilitation in oil-producing regions of the southern Urals

The technogenically induced salinization and alkalization (solonetzization) of gray forest soils results in their transformation into soils similar to natural solonchaks and solonetzes. Their density increases, the structure is disturbed, and the water stability of the aggregates becomes poorer. The humus content decreases, the nutrition regime is deteriorated, and the enzymatic activity is hindered. Under natural conditions, soil desalinization is seen within a ten-year-long period after its contamination with strongly saline oil-field waste water, while soil solonetzization remains very high. The soil properties are regenerated after application of an adequate rate of phosphogypsum and manure. Phosphogypsum applied alone causes a deterioration of the agrophysical properties as it produces an extremely high water stability of aggregates and strong soil compaction.     

The role of soils in the regional carbon budget of pine forests in Karelia

The carbon pool and its fluxes were studied in Karelian pine forests of automorphic sites for the characterization of the regional carbon cycle. On the permanent sample plots arranged in pine stands (dominant forest types) of the middle and northern taiga, the structure and dynamics of the phytomass, as well as the composition of the soil organic matter, were investigated. The contribution of different components of the forest ecosystems to the regional carbon budget was studied. The carbon pools in the soils of the middle and northern taiga subzones were 330–440 × 10² and 440–550 × 10² kg/ha, respectively. The share of soil carbon in the total carbon pool of the forest biogeocenoses studied amounted to 46–35 and 33–24%, respectively. The period of considerable carbon fixation in the pine ecosystem (nearly 20 × 10² kg/ha/yr) turned out to be limited to the middle-aged stands. In the mature and overmature pine forests, only 4 × 10² kg of C/ha/yr were fixed. The main part of carbon in the soil (65–75%) was contained in the illuvial horizons, although its content there was less that 1% as compared to 30–50% in the forest litters. On industrial harvesting of wood, the main reserves of soil carbon are not spent; only the fund of mobile carbon in organic horizons of poor soils is exhausted or carbon accumulates intensely due to the development of continuous plant cover on fertile soils.     

Clear-cutting affects the ammonia-oxidising community differently in limed and non-limed coniferous forest soils

The effects of clear-cutting on the ammonia-oxidising bacterial community were studied in the soil of limed and non-limed spruce forest plots located in the central part of southern Sweden. The communities were studied using denaturing gradient gel electrophoresis (DGGE) profiling after polymerase chain reaction (PCR) amplification from total DNA with primers reported to be specific for -subgroup ammonia-oxidising bacteria. The bands on the DGGE were sequenced and each unique sequence was interpreted as representing one ammonia-oxidising population. The relative abundance of each population was determined by measuring the fluorescence of the respective DGGE bands. In both limed and non-limed soil, the same two Nitrosospira populations were found, one belonging to cluster 2 (NScl2) and one to cluster 4 (NScl4). However, while NScl4 first appeared a year after the clear-cutting in the non-limed plot, it was present both before and after the cutting in the limed plot. Irrespective of previous liming, clear-cutting caused a shift in the ammonia-oxidiser community, from dominance by the NScl2 population to a community with approximately equal relative abundance of NScl2 and NScl4. In both plots the total size of the community increased after clear-cutting (based on increased DGGE band intensity), most likely due to increased NH₄⁺ availability, but the growth response was faster in the limed plot. Hence, the prior liming increased the responsiveness of the ammonia-oxidisers to the changes caused by cutting. This is the first study to report the effects of clear-cutting on the ammonia-oxidising community, and the results show a clear correlation between increased potential nitrification and a shift in the ammonia-oxidiser community.