Soil respiration (SR) is one of the largest fluxes in the global carbon cycle, exceeding anthropogenic CO2 emission by more than an order of magnitude. Estimation of the heterotrophic component of SR is necessary to assess the carbon balance on the ecosystem and on the regional, national, and global scales. Within the framework of the most important national innovation project “Development of a System of Ground-based and Remote Monitoring of Carbon Pools and Greenhouse Gas Fluxes on the Territory of the Russian Federation,” the first Russian national network is organized to monitor CO2 emission from soils and other linked parameters. The SR values and the relationship with the temperature of the upper 5- to 10-cm layer of soil (TS) are analyzed for the first time on the territory of Russia based on methodologically identical field measurements conducted simultaneously in the summer period (June–August 2023) at 75 monitoring sites in the different ecosystems in the main Russian bioclimatic zones from the tundra to the semidesert. The positive effect of soil temperature on the mean summer SR rate and the maximum monthly SR values is observed in the interval of mean TS from 10 to 20°C. Among the ecosystems studied, the lowest SR values are recorded in tundra and bog ecosystems, while the highest values are in the forest–steppe. Amongst the forest ecosystems, the lowest SR rates are characteristic of larch forests, while the highest SR values are observed in broadleaved forests of the forest–steppe zone. To clarify the regularities obtained, it is necessary to expand studies in all bioclimatic zones, but mainly in agrocenoses, tundra, and steppe ecosystems.

— The eluvozems and soddy eluvozems on two-layered deposits dominating in the soil cover of the Zvenigorod Biostation of Moscow State University, contain, on average, 65–83 t/ha of organic carbon in the organic layer and the upper meter of mineral strata. Carbon stock is minimal (59–68 t/ha) in the coarser-textured soddy eluvozem of the spruce forest and reaches 76–92 t/ha in soils of birch–spruce and pine–spruce forests. Organic layers store 3.3–5.8 t C/ha or 4–9% of the total soil organic carbon stock; the upper mineral layer (0–20 cm) stores 64–69%. Different levels and profile distribution of organic carbon in soils are determined by lithological and textural features of the soil profiles and by the nature of vegetation. The contribution of water-extractable organic carbon to the total organic carbon content in the upper mineral horizons does not exceed 1.3–1.8%; the contribution of microbial carbon is 1.7–2.4%. In acidic loamy soils, the enrichment in calcium and potassium, the cation exchange capacity, the content of exchangeable bases, and the degree of base saturation can serve as indicators of the content and stocks of organic carbon at the ecosystem level. The relationship with the content of clay fractions and oxalate-extractable Al and Fe is manifested to a lesser extent due to the similar origin and properties of soils. The variability of organic carbon stocks in soils is largely determined by its content, the influence of which decreases with depth. Accounting for spatial heterogeneity, field measurements of the soil bulk density and proportion of fine earth, and correct analytical determinations are essential components of the assessment of carbon stocks in soils of forest ecosystems as a part of the national monitoring system for carbon pools and greenhouse gas fluxes.

A reliable assessment of the composition and properties of soils in forest ecosystems is the basis for environmental monitoring, including monitoring of carbon pools and fluxes, which is of particular importance in the context of global changes in the natural environment and climate. Ecological and genetic features and classification of soils are analyzed at permanent sites of intensive monitoring in the main types of forest ecosystems of the state nature reserve “Zvenigorod Biostation of Moscow State University and the Sima Quarry” (Moscow Region, Russia). Soil monitoring is organized and conducted on the basis of national experience and recommendations of the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests). Eluvozems and soddy-eluvozems on two-layer deposits dominating in the soil cover of the reserve are characterized by a sandy loam texture (content of clay fraction 0.002 mm 3.3–7.0%), acidic reaction (\({\text{{р}}}{{{\text{{Н}}}}_{{{{{\text{{Н}}}}_{{\text{2}}}}{\text{{О}}}}}}\) 4.6–5.7), low cation exchange capacity, low content of exchangeable bases (30–52 cmolс/kg in organic and 0.6–7.5 cmolс/kg in mineral horizons) and low base saturation (49–67 and 11–51%, respectively). The content of potentially toxic metals (Pb, Cd, Cu, Ni and Zn) in the soils of the reserve does not exceed background levels. The ecological state of soils improves in the series of contact-albic eluvozem – pseudofibrous soddy eluvozem – ferruginous soddy eluvozem, determining the stability of forest ecosystems to external effects under conditions of increasing anthropogenic pressure and climate change.

At the international level, the concept of critical loads developed under the Convention on Long-Range Transboundary Air Pollution directed by the United Nations Economic Commission for Europe is actively used to assess the risks of excessive inputs of pollutants into ecosystems. The review considers the main principles of the concept of critical loads and methods of its application for assessing the current risks of excessive accumulation of heavy metals (HMs) in soil as a component of terrestrial ecosystems from the standpoint of ecotoxicological effects (on plants, soil invertebrates, and microorganisms). Under this concept, the critical concentrations of Cd, Pb, Cu, and Zn for soils are for the first time estimated using the functions of critical concentrations taking into account the properties of soils (primarily, acidity and the contents of organic matter and clay). The main attention is paid to the rationale and development of the models for assessment of the critical concentrations and transfer functions connecting the concentrations of HM compounds in soils and soil solutions. The current environmental risks of excessive HM accumulation are assessed by comparing them with their critical concentrations. Current challenges and future prospects for analyzing the current environmental risks based on the concept of critical loads include the reduction in the uncertainty of estimates, combined effect of different metals in a multicomponent pollution, field validation of processes and modeling results, and the impacts of climate change and land use.

Widespread industrial pollution and its serious ecological and economic consequences make it urgent to develop and refine approaches to remediation of soils as a key ecosystem component. The long-term impact of atmospheric emissions from nonferrous metallurgy enterprises in Monchegorsk (Murmansk region) resulted in the formation of technogenic barrens with contaminated and highly degraded soils near the pollution source. During long-term monitoring, the current status and dynamics of soil properties have been assessed on permanent control plots on barrens and in birch and willow plantations after remediation performed in 2003–2008 by two methods: chemophytostabilization and covering of contaminated soils by an artificially created fertile layer. The research data of 2011, 2015, and 2018 indicate the continuing acidification of soils and their contamination by heavy metals. Despite the reduction in emissions, the concentrations of available heavy metals in the topsoil of barrens and chemophytostabilized plots do not decrease, and the constructed layers accumulate nickel, copper, cobalt, iron, cadmium, lead, and manganese. The nutrient supply of soils is steadily improved only when a fertile layer is applied. According to the results of the multivariate analysis, the soils of barrens and remediation plots are clearly separated in the space of the first two principal components as the soil properties are improved during remediation, and the positions of chemophytostabilization plots reflect the unstable improvements. Recommendations for the development of a strategy and diversification of methods for remediation of technogenic barrens should take into account different levels of soil pollution and degradation in the vicinity of nonferrous metallurgy enterprises and the need to comply with technological requirements and perform supporting measures.

To assess the state of plants and their response to changes in soil properties, the elemental composition of leaves of widespread and pollution-tolerant species Betula pubescens Ehrh. and Salix caprea L. has been studied near the nonferrous metallurgy enterprises in the Kola Peninsula. The content of nutrients and heavy metals in the leaves of undergrowth on technogenic barrens and remediation sites differing in remediation technologies has been analyzed. According to the results of leaf diagnostics, both species under barren conditions are characterized by a noticeable deficiency of K, Ca, P, and, especially, Mn and Zn. The leaves of both species accumulate Ni, Cu, Co, As, Cr, Fe, Al, Pb, V, and S. Willow leaves contain more Cd, Co, Cr, Ni, Cu, Al, Fe, As, S, Ca, K and less Mn than birch leaves. Chemophytostabilization has little effect, and the covering of contaminated soils with a constructed fertile layer leads to the enrichment of birch and willow leaves with Ca, K, and P. Under conditions of continuing atmospheric emissions and gradual accumulation of bioavailable heavy metals in soils after the remediation, the accumulation of metals in leaves is largely determined by the distance from the pollution source, reflecting the possibility of both root and foliar uptake. The concentrations of Ni and Cu in leaves in 2018 did not decrease compared to 2011. The low, albeit varying, ratios of the contents of heavy metals in undergrowth leaves and in the soil and weak correlation of heavy metal contents in these media indicated that B. pubescens and S. caprea retain their ability to regulate their chemical composition even under extreme conditions of technogenic barrens. At the same time, supporting the protective capabilities of plants via optimizing mineral nutrition and soil acidity in combination with a reduction in atmospheric pollution is a prerequisite for efficient remediation of technogenic territories in the Far North.

A detailed analysis of the current state of knowledge of the problems and prospects for phymoremediation of metal(loid) polluted soils illustrate that phytoextraction and phytostabilization have been the foci as widespread and alternative methods of soil phytoremediation. This chapter focuses on the enhancement of phytostabilization by the use of organic soil amendments. The number of publications on organic amendments in phytostabilization of heavy metal(loid) (HM) contaminated soils increases each year and covers all studied groups of additives – composts, sewage sludge/biosolids, humic substances and, especially, fast growing biochar. From the range of forestry by-products such as sawdust, bark chips, and woodchips, pine bark has been demonstrated to be an effective sorbent of both HMs and hydrocarbons. Development of soil remediation approaches for lands contaminated with HMs in recent decades has led to the implementation of a variety of potential technologies.

The long-term emission impacts of the nickel processing industry in the Kola Peninsula, the largest source of sulfur dioxide and heavy metals emissions in Northern Europe, have created vast technogenic barrens near the mineral industry complexes. The pace of rehabilitation using the improved remediation technologies to enhance sustainable environmental management and regional economic development is of crucial social and economic importance. In a 120-day incubation experiment, we evaluated the prospects for the restoration of two soils at different degradation stages via carbon pool regulation comparing to mineral ameliorants – NPK fertilizer, and liming agent. Organic additives used included a humic preparation based on an alkaline brown coal extract, wood-derived biochar, and peat-derived gel, supplied by mycorrhizae fungi. The results demonstrate that the selected organic amendments are suitable for restoration of acidic metal contaminated soils. Specifically, the treatments provided a measurable increase in soil carbon content, a marked decrease in acidity, a decrease in extractable metal contents, together with an enhanced nutrient uptake and vegetative growth. A stabilization effect increased from biochar to peat-gel, liming agent and humic preparation, with an accompanying increase in soil pH. Although biochar showed a reduced ability to metal stabilization, the associated treatments were the most productive. The most effective amendments in multi-metallic contaminated soils need to be able to stabilize bioavailability of metals, adjust pH to the optimum for plant growth, and regulate nutrient consumption.

The total soil CO2 efflux and its constituents were analyzed along the gradients of pollution of forest ecosystems by the emissions from nonferrous metallurgy plants in the Kola Subarctic. The CO2 efflux from the soil surface was measured by the closed chamber method. The summer efflux was calculated using the regression dependences of CO2 emission on air temperature. The root and microbial respirations were separated using the field method of substrate-induced respiration. The soil CO2 efflux reached relatively high values in the background pine (200 g C/m2/summer), birch (460 g C/m2/summer), and spruce (420 g С/m2/summer) forests. The bulk of CO2 produced in the soils under these forests was due to root respiration (45–70%). Closer to pollution sources, a decrease in microbial and plant biomass, depletion of mineral nutrients, and accumulation of heavy metals were observed in soils. As a result, the CO2 efflux decreased by up to 1.5 times in the zone of defoliation of the trees, 10 times in the zone of technogenic sparse forests, and 20 times in the zone of technogenic barrens. Defoliation of forests was accompanied by some activation of microbial respiration because of the additional input of nutritional substrate for microorganisms. The degradation and death of vegetation resulted in an expectable decrease in root respiration and its complete suppression in technogenic barrens. The results of this study indicate that monitoring of the soil CO2 efflux helps to identify the specific features in the functioning of forest ecosystems during technogenic degradation and to develop efficient methods for their remediation under industrial pollution in the Arctic.

In short-term incubation experiment (90 days with additional preincubation) in conditions, simulating summer season in Kola Peninsula, Russia, we implemented different organic amendments — humic subtances, peat-gel, biochar — for remediation of highly contaminated soils of technogenic barrens, situated in 2 and 5 km from active nickel processing industry. Unamended soils used in experiment are characterised by ablation of upper fertile soil layer, high acidity, high content of Ni, Cu, Fe, Zn, depletion of nutrients and organic matter, and, as consequence, by the absence of natural vegetation. To predict potential influence of amendments on contaminated soils and their capacity to immobilise HM bioavailable forms and improve soil health we provide data of structural characteristics with and without additional preparations evaluated by Fourier-transformed infrared (FTIR) spectroscopy and Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Our data support the idea of high importance of organic amendment structural characteristics and link these characteristics with observed soil physical, chemical and ecotoxicological properties. This study was funded by Russian Foundation for Basic Research according to research project No. 18-04-01028, high-resolution mass spectrometry was supported by Russian Science Foundation grant No. 19-75-00092.

This research aim was testing the applicability of exogenic organic matter – extracted humic substances – for the remediation of technogenic barrens soils near Cu-Ni smelter (Kola Peninsula). In short-term laboratory experiments we studied the possibility of stabilization of heavy metals labile forms by commercial humic substances (HS) of different origin (peat humate “Flexom” and coal humate “Extra”) in comparison with HS, inoculated by microorganisms – nitrogen fixers and mycorrhizae-forming fungi and mineral fertilizers (NPK и CaCO3). Experiments were provided during 45 days after 14 days of pre-incubation under controlled conditions in climate chamber with light, temperature and humidity imitating the polar day conditions in Kola Subarctic. After experiments we evaluated changes in soil chemical properties, soil microbial community and test-culture (Deschampsia cespitosa). Peat humate application is ineffective without additional manipulations (e.g. combination with CaCO3), cooperation with biological applicants cannot be pointed out. Application of coal humate favours to metals stabilization, soil microorganism’s activation, test-culture growth. It may be effective to combine coal humate with biological applicants like mycorrhizae-forming fungi. So, coal-humates may be perspective growth-stimulator, ameliorant and detoxicant in remediation of degraded soils in conditions of polymetallic contamination.

Technogenic barren lands formed under the influence of sulfur dioxide and heavy metal emissions near nonferrous metallurgy enterprises on the Kola Peninsula are characterized by inhibited CO2 emission from soils (10–30 mg C m–2 h–1, or 12–26 g C m–2 summer–1). Remediation of barrens promotes the growth of plant roots and microorganisms, the respiration of which accelerates the flow of CO2 from the soil by half at chemophyto stabilization and five times at application of the fertile layer; at this, the proportion of root respiration increases from 0 to 40–60%. The intensity of CO2 emissions by soils and the structure of its production can be used as criteria for remediation effectiveness of technogenic barren lands.

In a three-month experiment influence of different organic amendments (coal humate, peat-gel, biochar) in comparison with mineral ameliorants (NPK and CaCO3) on chemical and physical properties of soils at different stages of degradation has been shown. Objects of the research were abrazem and podzol soils of technogenic barrens near Monchegorsk city, Murmansk region (Russia). Festuca rubra was used as a test-culture. According to the obtained data, we can conclude that organic applicants may be suitable for remediation of soils, contaminated by heavy metals. Applicants, selected for the experiment, unequally affected the soil properties and the test-culture growth. For the most disturbed and contaminated soils - abrazems -we suggest coal humate and calcium carbonate as the most promising additives for both toxicants' immobilization and preventing bioaccumulation. Biochar and peat-gel in the tested concentration showed a more expressed positive effect on podzol soils with a lower level of contamination. In both soils, abrazem and podzol, biochar favors to the test-culture growth more, than other amendments. The potential advantage of used organic amendments, coal humate and biochar, in contrast to ameliorants is their ability to improve the physical soil properties.

Background. The increasing technogenic pollution actualizes the restoration of vegetation cover in many industrial regions of the planet, including the vicinity of non-ferrous metallurgy enterprises in the Kola Subarctic. The barrens podzols and abrazemes are unfavorable for plant development. The study is aimed at assessing the restoration of vegetation as a result of the mine lands remediation near the Severonickel industrial complex. Materials and methods. Remediation was carried out in 2003–2008 by two methods: chemophytostabilisation (without pretreatment of the soil) and overlapping of contaminated soils with organic matter–rich cover materials followed by liming, fertilization, seedlings planting and grass mixture sowing. The species composition and the projective cover of the vegetation, the vital status of the undergrowth, the aboveground phytomass of the ground cover and the thickness of the upper soil layer were evaluated at 11 monitoring sites taking into account spatial variation. Areas of barren lands were considered as control. For the evaluation and graphical display of the characteristic features of the vegetation variability, the principal component analysis (PCA) was used. Results. According to the state of the vegetation, the chemophytostabilisation sites only slightly differ from the control barrens sites due to adverse edaphic conditions. Planted trees and shrubs have a strongly depressed appearance and a low projective cover, and the ground cover is not restored. On remediation sites with organic matter–rich fertile layer, sparse deciduous young stands are formed with a predominance of goat willow and / or fluffy birch, with a higher level of tree vitality and species diversity, grass cover with the participation of grass and / or horsetail. The PCA revealed an objective fractioning of sites according to the vegetation condition depending on the remediation technology. Conclusions. Successful restoration of vegetation in mine lands in conditions of emissions reduction depends on the state of the soil and the technology used. Environmentally friendly and cost-effective chemophytostabilisation gives only a short-term effect that needs continuous maintenance. A more promising but expensive way to quickly restore the barren lands is to apply a constructed fertile layer to the surface of polluted soils in combination with the planting of deciduous trees and the sowing of perennial grasses.