Research Highlights: It was found that both tree species and ground vegetation affected soil carbon stock in boreal forests. Carbon stocks in the mineral layers were related negatively to the C/N ratio in the organic horizon and pine proportion in the growing stock volume, and positively to the share of herbaceous plants and the proportion of spruce. Background and Objectives: Existing research showed the effects of tree species on soil carbon stocks in organic horizons, but these effects were less clear in mineral horizons. Little is known about the effects of ground vegetation on soil carbon stock. This study aims to identify associations between the forest vegetation composition and soil carbon stocks in northwestern Russia. Materials and Methods: Research data from 109 pine, spruce and birch forests of different Cajander’s and Sukachev’s types with different functional compositions of ground vegetation at autonomous positions are discussed in this paper. The V-test was used to assess the impact of vegetation on soil carbon stocks. Results: Variations in Carbon stocks in the mineral layers were associated with the soil types and vegetation composition. Carbic Albic Podzols accumulated the least amount of carbon in the mineral profile. Carbon stock in the mineral layers in pine forests was considerably lower than in spruce and birch forests. Spruce forests with the highest share of herbaceous plants were characterised by the highest carbon stocks in the mineral layers, while pine forests with dwarf shrubs and green mosses accumulated more carbon in the organic layers, but carbon stocks in the mineral layers here were the lowest. Conclusions: Differences in soil carbon stocks between and within northern and middle taiga in northwestern Russia were associated not only with soil types but also with the proportions of forest types dominated by different tree species and ground vegetation functional groups.

Linking vegetation, soil biota, and soil carbon stocks in forests has a high predictive value. The specific aim of this study was to identify the relationships between vegetation, earthworms, and soil carbon stocks in nine types of forests dominating autonomous landscape positions in a coniferous–broadleaf forest zone of the European part of Russia. Mountain forests were selected in the Northwest Caucasus, while plain forests were selected in Bryansk Polesie and on the Moskva-Oka plain. One-way analysis of variance (ANOVA) and v-tests were used to assess the impact of different factors on soil C stocks. To assess the contribution of vegetation, litter quality, and earthworms to variation of carbon stocks in organic (FH-layer) and mineral layer (0–50 cm), the method of hierarchical partitioning was performed. The highest C stocks in the organic horizons were associated with the low-quality litter, i.e., with a low base saturation, high acidity, and wide C/N ratio. The highest soil C stocks in the mineral layers were found in mixed forests with the highest richness of plant species, producing litterfall of different quality. The C stock in the organic horizon was negatively related to the biomass of worms that process the litter, while the carbon stock in the mineral layers was positively related to the biomass of worms whose life activity is related to the mineral layers. These findings demonstrated the substantial influence of plants producing a litter of different quality, and of earthworms, belonging to different functional groups, on soil C stocks in coniferous–broadleaf forests.

A comparative assessment of carbon accumulation in the soils of pine forests in western Russia (the Republic of Karelia, the Karelian Isthmus, and Bryansk region) developed on coarse-textured parent materials has been made. The total carbon stock in the litter and upper soil layer (0–50 cm) varied from 47 t/ha in the soils of pine forests of Bryansk region to 116 t/ha in the soils of pine forests of the Karelian Isthmus. It has been shown that the main factors of carbon accumulation in the soils of pine forests in western Russia were the climate, parent materials, vegetation, agricultural activity, and fires. The influence of climatic conditions has been clearly manifested in the levels of carbon accumulation in the litter and in the upper humus-accumulative soil horizons. In the pine litter within the zone of mixed forests (Bryansk region), the level of carbon accumulation was the lowest, whereas the litter layer of pine forests in the northern taiga (Karelia) has the highest stock of carbon. At the same time, the lowest carbon stocks in the upper mineral soil layers has been noted for the soils of northern taiga forests, which had no humus-accumulative mineral horizon. The variability of carbon stocks in the litter layer was largely controlled by the C/N ratio, as well as by the fraction of deciduous undergrowth and grasses producing high-quality litter. The influence of agricultural activity on soil carbon stock in pine forests was especially pronounced on the Karelian Isthmus with the high agricultural activity in the past, as well as in Bryansk region, where pine forests are formed from pine plantations. The effect of fires on soil carbon stock was most pronounced in heather and lingonberry pine forests of the northern taiga of Karelia.

Existing estimates of carbon stocks in taiga and coniferous-deciduous forests show that almost half of the total organic carbon in these ecosystems is accumulated in forest soils. Vegetation as the main source of organic matter in the soil, interact with soil biota, which processes plant litter, and with abiotic environmental factors, determines the processes of formation and accumulation of soil organic matter. Changes in the composition of vegetation are the driver of the dynamics of soil carbon stocks; however, insufficient attention has been paid to the analysis of this issue. The review analyzes the main ways of transferring carbon from the vegetation pool to the soil pool and the influence of three main predictors of vegetation that affect the carbon stock in soils: the amount and quality of litter of individual species (species identity) of plants and the structural diversity of the plant community; gaps in knowledge and the ways of development of this scientific direction are proposed.

Being the crucial part of the forest soil's microbial pool, soil fungi in general and mycorrhizal fungi in particular are an important study object when it comes to forest ecosystems sustainability and preservation. Thus, the study of ectomycorrhizal fungi has been carried out in the Bryanskiy Les State Nature Biosphere Reserve, located in the south-eastern part of the Bryansk woodlands (European Russia). Forest types featured in the study are the local predominating types, namely green-moss-fructiculose pine forests and polydominant deciduous broadleaved nemoral-herbaceous forests with spruce. This study was aimed to assess seasonal dynamics of soil fungi' biomass overall and ectomycorrhizal fungi in particular over the course of the 2017 vegetation period (May – November) and its dependence on biotic and abiotic environmental factors, such as soil water content, temperature and vegetation. The vegetation period was divided into three periods of observation, namely an early (May – July), middle (July – September) and late (September – November) one. The method used to assess the fungal biomass was direct microscopic observation using the fluorescein diacetate staining. In order to estimate the ectomycorrhizal fungi biomass separately, trenching and in-growth mesh bags were employed. The obtained results suggest that the soil fungi biomass steadily increases over the vegetation period in both studied forest types. This is mostly affected by the forest type, available water amount and seasonal changes, while the temperature's impact is less pronounced. On average, the soil fungi biomass was higher in broadleaved forests than in pine forests (2.288 mg C × g-1 soil vs. 1.672 mg C × g-1 soil, respectively), with non-ectomycorrhizal component having comparable biomass. The dynamics of biomass differed in the two forest types. However, noticeable differences (p < 0.1) between the two forest types have only been recorded during the July – September period. The biomass of ectomycorrhizal fungi is smaller than the biomass of non-mycorrhizal fungi, but at the same time it is less affected by changes in moisture. Besides that, the study has shown that the forest litter characteristics can greatly affect the dynamics of the fungal biomass.

The problem of assessing carbon fluxes and pools in forests is acute due to climate change and contribution of forests to carbon reserves. The papers provides a comparative assessment of carbon ingress with atmospheric precipitation and leaching the dissolved organic carbon from soils under coniferous–deciduous forests of different types on sandy soil-forming deposits. The dominant types of coniferous–broadleaved forests of the Bryansk region, i.e., dwarf shrub–green moss pine forests, composite boreal–nemoral herbaceous pine forests and polydominant broadleaved nemoral-forb spruce forests are the objects of study. On average, over a three-year-long observation period (2016–2019), the carbon ingress with rain and snow was 60 ± 4 kg C/ha per year in shrub–green moss and composite pine forests; this turned out to be higher than in coniferous-broadleaved forests, where the carbon input was 47 ± 2 kg C/ha per year. The removal of organic carbon from organic horizons in polydominant broadleaved forests was four times lower (14 ± 4 kg C/ha per year) on average than in dwarf shrub–green moss pine forests specified by a thick litter (56 ± 22 kg C/ha per year), and 2.5 times lower than in composite pine forests (36 ± 12 kg C/ha per year). The cases of leaching organic carbon from the lower mineral horizons were scarce for different types of coniferous-deciduous forests and varied on average from 6 to 12 kg C/(ha year). The distribution of dissolved organic carbon in the soil profile shows a more efficient carbon fixation in the mineral part of soil profile in pine forests than in polydominant broadleaved forests.