No 11 (2024)

On the basis of data from 67 sample plots located in different natural-climatic zones on the territory of Krasnoyarsk region and in mountain forests of the western and eastern Baikal region (Irkutsk region and Republic of Buryatia), the contribution of belowground plant residues to the soil carbon stock was estimated and the main factors influencing the stock of root detritus were analyzed. The studies were carried out both in undisturbed old-growth forests and in forest ecosystems affected by clear-cutting, forest fires and aerotechnogenic pollution. It has been shown that the carbon stock accumulated in root detritus can be quite comparable to that in forest litter, and in some cases can exceeding it by a factor of 1.3–1.9, and accounting for between 3.6 and 167% of the carbon stock in soil humus. This stock and its contribution to the soil carbon pool depends on the forest forming species, the soil type and the natural climatic zone, and can increase significantly after the impact of disturbances that destroy above-ground vegetation and plant residues on the soil surface. Underestimating this component in the assessment of forest ecosystem carbon budgets can lead to an underestimation of total soil carbon stocks by 5–32% in undisturbed forest ecosystems and up to 40% after various types of disturbance.

A research polygon with the area of 15 ha was established as an object of climatic monitoring in 2022 in Shchelkovsky district of Moscow region. Within the polygon, representing one forest survey unit, а high taxonomic diversity of soil cover was revealed: 18 taxonomic unit of various hierarchical levels, from subtype to variation. Microrelief is regarded as a leading factor of carbon stock diversity: soils of drainless micro-depressions under sphagnum moss cover significantly differ from the main sampling by carbon stock in litter and upper 10 cm of soil. For the greater part of the polygon, the most important factors determining carbon stock are the percent of physical clay in the subsoil, the composition and phytomass of forbs. The largest coefficient of variation of C stocks (40%) was obtained for the layer 10–30 cm and is related, first of all, to the variation of thickness of incorporated soil horizons. The geospatial analysis allows us to make spatial evaluation of soil properties diversity, model and forecast soil carbon stock dynamics considering spatial heterogeneity of the territory. Detecting the factors controlling soil carbon stocks would be helpful in the formulation of modelling scenarios; the latter simulate the activities aimed at the increase in carbon accumulation in forest ecosystems via the management of vegetation structure.

Integrated surveys were carried out in a carbon testing ground in the Kivach State Strict Nature Reserve, which represents relatively undisturbed East Fennoscandian mid-boreal ecosystems. The forest floor is a heterogeneous body with considerably variable composition and condition. In the study area there predominate (80% of all sampling points) coarse-humus fermentation-type forest floors with an average thickness of 5.2 ± 0.2 cm and stock of 48.0 ± 2.0 Mg/ha. As the residues decompose, they gradually lose organic matter. The highest С_org levels (52.8 ± 0.6%) in the testing ground’s most common subshrub-true moss habitats are found in the top layer of the forest floor. In the lower sub-horizons, carbon content declines – 40.8 ± 2.0%. In habitats with a higher contribution of forbs, С_org content decreases considerably – to 19%. Average С_org stock in the forest floor of the surveyed ecosystems is estimated at 20.9 ± 0.9 Mg С_{org /}ha. The data exhibit high spatial variation – from 1.5 to 45 Mg С_{org /}ha. The variation of С_org stock in the forest floor across the study area is predicated on the following: ground cover characteristics, prevalence of a tree species and position within the tree’s impact zone.

The purpose of this study was to study the structure of microbial communities, the physicochemical characteristics of the soil profile of brown soils and the soil material of humus pockets. Brown soils (Cambisols), located in the south of the Vitim Plateau, are characterized by a peculiar morphological structure – the presence of frost cracks, which form wedge-shaped humus pockets, sharply tapering down the profile. Humus pockets are filled with dark brown humus material with black stripes that contrast sharply in color and properties with the surrounding soil profile. Compared to the profile of brown soils at corresponding depths, the soil mass from humus pockets is less compacted. An increase in total porosity leads to an increase in water permeability of the humified mass of frost cracks. Features of the structure of microbial cenosis and carbon of microbial biomass of brown soils in the soil profile and in the soil material of pockets were revealed. In the soil material of the pockets, the content of organic carbon and the amount of absorbed bases are distributed relatively evenly, while in the soil profile the indicators sharply decrease down the profile. Experimental data obtained during the study will replenish the database on the properties and state of microbial cenosis in brown soils and in the soil material of humus pockets of brown soils in the south of the Vitim Plateau.

The results of a quantitative assessment of carbon pools and fluxes in a mid-taiga coniferous-deciduous forest and their changes after clear-cutting are presented. It was shown that up to 14.7 kg C/m² accumulated in the original forest. The main reserves are concentrated in the biomass of the tree stand (62.4%), soil (35.5%), biomass of ground cover plants (1.1%) and large woody debris (1.0%). During the cutting process, 6.57 kg C/m² is removed as part of the stem wood (44.8% of the total carbon reserves of the ecosystem or 71.79% of the carbon of the biomass of the tree stand). In the first year after logging, 8.1 kg C/m² was detected in the ecosystem. Of these, 7.1% of carbon reserves are in forest vegetation, 66.8% (5.4 kg C/m²) are concentrated in the soil. During clearing, the share of large woody residues increases significantly (1.9 kg C/m²) (23.4% of ecosystem reserves) due to the appearance of logging residues that have died as a result of felling, which in the future will have an impact on the flow of carbon dioxide into the atmosphere from its territory. As a result of clear cutting, the supply of wood litter to the soil surface is reduced by 42 times. The decomposition of organic matter inherited and produced during wood harvesting slightly (≈ 10%) increased the supply of carbon through soil respiration. Logging leads to a decrease in carbon removal from litter. The data obtained will be used in assessing the impact of clear-cutting on the carbon cycle of taiga ecosystems.

In the coastal zone of Lake Shira (Republic of Khakassia), in forty-year-old artificial forest plantations of Siberian larch, elm and Scots pine growing on dark light and medium loamy accumulative-calcareous agrozem (Chernozems), the state of microbial communities in the soil, as well as the degree of their degradation and the production ability after strong ground fire 2015 were assesed. Soil condition was investigated by physicochemical, microbiological, enzymological and respirometric research methods. In 2015 (after the fire), due to the significant supply of pyrogenesis products into the soil studied plots, high values of microbial biomass (MB, 3458 mg C/g soil) and intensity of microbial respiration (BR, 12.23 μg C–CO₂/(h d)) were recorded. In the first years after the fire (2017–2019), a decrease in the content of humus and biophilic elements was observed in the soil, as well as a slowdown in the activity of carbohydrate and phosphorus metabolism. At the same time, in 2017 the highest level was recorded for the entire observation period cellulose-decomposing activity due to intensive mineralization of burnt plant residues. By 2023, a gradual increase in humus content and activation of mineralization processes led to an increase of the total number of soil microorganisms, the content of microbial biomass, and a significant decrease in the values of the microbial metabolic coefficient All these marks indicate a tendency to restore the functional activity of the soil microbocenoses. It was shown that the soil biological activity in the postfire areas were restored faster than in the postconflagration areas, while the stand species influenced the main soil parameters, which differed from each other, as confirmed by principal component analysis.

The natural structure of the ecosystems in the lower-middle mountain belt of the North-Western Caucasus is predominantly represented by secondary woody communities, with a minor presence of steppe ecosystems. The soil cover of this area consists of a combination of natural types: Cambisols and Rendzic Leptosols. Cambisols dominate under downy oak forests, while Rendzic Leptosols, which were once formed under hemitherme (Mediterranean) steppes, have undergone significant changes and are now found under downy oak shrublands, ash communities, and lime groves, as well as under preserved steppe vegetation. Consequently, there is a decrease in soil organic carbon (SOC) content in the soil-successional series: Rendzic Leptosols leached soils under herbaceous communities, Rendzic Leptosols leached soils under woody communities, and Cambisols. The functioning of Rendzic Leptosols soils under woody phytocenoses and their further succession according to the cambisol type reliably reduces SOC content to a depth of up to 60 cm. In contrast, SOC content in Rendzic Leptosols soils under herbaceous phytocenoses is higher not only in the humus-accumulative horizon but throughout the entire profile. The most significant changes in the humus composition affect its water-soluble fraction, extracted by cold and hot extraction. Cambisols and Rendzic Leptosols soils under woody phytocenoses are characterized by a similar accumulation pattern in the surface horizons of the easily soluble fraction of water-soluble organic matter (cold extraction) and its profile distribution. Meanwhile, the absolute values of water-soluble organic matter (hot extraction) in the profile of Rendzic Leptosols soils under woody formations are almost halved compared to soils under herbaceous phytocenosis. The decrease in humification of Rendzic Leptosols soils during the formation of forest communities occurs due to the destruction of the organic part, which was once strongly associated with calcium and undergoes maximum transformations due to the change in plant litter and microclimate under the trees. Soil acidity affects the degree of water-soluble organic matter extraction – the proportion of the hot fraction of water-soluble organic matter in SOC significantly increases with a decrease in solution pH.

This study aims to assess the relationships between SOC content and main soil-forming factors and identify key factors explaining the spatial distribution of SOC. The research was conducted in the Southern Ural Mountains throughout 420 km from north to south in the Republic of Bashkortostan. The predominant soil types are mountainous gray forest (Eutric Retisols (Loamic, Cutanic, Humic)), dark gray forest (Luvic Retic Greyzemic Someric Phaeozems (Loamic)) soils, and gray-humus lithozems (Eutric Leptosols (Loamic, Humic)). Forest stands are mainly composed of birch (Betula pendula), pine (Pinus sylvestris), spruce (Picea obovata Ledeb.), and fir (Abies sibirica Ledeb.). A data set of 306 soil samples taken from the top layer (0–20 cm) was studied using the “random forest” machine learning method. Ninety-four spatial environmental covariates were used as explanatory variables, including remote sensing data, climate (temperature, precipitation, cloudiness, etc.), digital elevation model and its derivatives, land uses, bioclimatic zones, etc. The results showed that the SOC content varied widely from 0.8 to 32%. The random forest predictive model explained 55% of SOC variation (R2) with a root mean squared error (RMSE) of 1.35%. Key variables included surface temperature, absolute elevation, precipitation, and cloudiness, which together reflect the Dokuchaev vertical and horizontal zonality laws. The findings emphasize the importance of considering multiple environmental factors in subsequent research focused on assessing the spatial distribution of SOC.