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 article presents the results of a quantitative assessment of biotic and abiotic factors influencing leaf litter decomposition rates in forest ecosystems of the Valuyevsky Forest Park, Moscow City, accounting for spatial heterogeneity across three hierarchical levels, namely: biogeocoenosis type (Spruce-Oak forest with oxalis and herb-rich and Lime-birch forests with hairysedge), parcel (plots with closed canopy and forest gaps), and elementary biogeocoenotic area (EBGA). A field experiment conducted from November 2021 to November 2022 employed the litterbag technique with mesh sizes of 0.2 mm and 4 mm to monitor the decomposition dynamics of lime ( Tilia cordata ), birch ( Betula pendula ), and oak ( Quercus robur ) leaf litter. Concurrent measurements included the biomass of soil saprophages, fungi, bacteria, and hydrothermal environmental parameters. It was established that leaf litter quality is the dominant regulator of the decomposition process, accounting for 32% of the variation in decomposition rates. The contribution of soil macrofauna amounted to 9%: access of macro-saprophages accelerated lime litter decomposition by 1.5 times, whereas oak litter was predominantly transformed by microorganisms. The influence of vegetation structural diversity operates indirectly – through shaping litter quality and microclimatic conditions. In communities dominated by high-quality litter (lime-birch forests), preserving the functional diversity of saprophages intensifies biological cycling; in contrast, in communities with prevalent low-quality litter (spruce-oak forests) but a more pronounced parcel structure, the key role is played by the interaction between hydrothermal conditions (precipitation volume, temperature) and soil biota. The results substantiate the necessity of enhancing and maintaining intra-biogeocoenotic heterogeneity in forest ecosystems.