CHANGES IN THE CONTENT AND DIVERSITY OF SOIL BACTERIA UNDER DEADWOOD OF VARIOUS TREE SPECIES AFTER WINDTHROW IN OLD-GROWTH BROAD-LEAVED FORESTS

Soil bacteria play a key role in the functioning of forest ecosystems, regulating many biochemical processes such as the transformation and mineralisation of organic matter, nitrogen fixation and carbon sequestration. Deadwood is an important element of forest ecosystems, but the impact of windfalls and deadwood on the diversity and structure of soil bacterial communities has been little studied. Taking into account the diversity of habitats associated with windthrow of different tree species allows us to assess the spatio-temporal dynamics of the abundance and composition, as well as the functional specificity of bacterial communities. The study analyzed the bacterial DNA content, diversity and structure of soil bacteria in Podzols, Retisols and Phaozems of broad-leaved forests in areas of mass windthrow, under fallen trunks of seven tree species and in background forests. Profiling microbial communities using 16S sequencing , conducted for the first time in multi-species old-growth broad-leaved forests, revealed a high diversity of soil bacterial communities. The predominant bacterial groups were Alphaproteobacteria and Verrucomicrobiae, and in Podzols also Planctomycetia. The main factor influencing bacterial DNA content, diversity and community structure was soil texture. In loamy soils, the bacterial DNA content and alpha diversity of bacteria were higher than in sandy soils. The results confirmed the hypothesis that species affiliation of fallen tree has a significant impact on forest soil bacterial communities. At the same time, the structure of bacterial communities is quite conservative, with the most pronounced changes observed under fallen trees with special wood properties (Quercus robur, Picea abies, Acer platanoides). A significant number of unique taxa were found in windthrow areas and under fallen trunks, accounting for more than half of the total number of ASVs identified. It has been concluded that single and mass windthrows, as well as the simultaneous presence of fallen trees of various tree species, significantly increase the bacterial diversity of forest soils, thereby contributing to the functional sustainability of forest ecosystems.