Variability of Anatomical Characteristics of the Wood of Mountain Ash (Sorbus aucuparia L.) in the Conditions of the North Caucasus

The article presents the results of a study of the structure of the wood of mountain ash (Sorbus aucuparia L.) in the mountains of the North Caucasus. The direction of adaptive changes occurring in the elements of the secondary xylem of the plant at various heights, including extreme ones, is shown. The conclusions of a number of studies have been confirmed that the basic reaction of mountain ash with an increase in altitude and a decrease in growing capacity, as well as an increasе in the intensity of transpiration, is a decrease in plant size and a narrowing of the annual growth of the stem in diameter. At the same time, a number of quantitative changes occur in the wood itself, mainly aimed at optimizing the water-transporting function. With increasing altitude, as water supply conditions become more stringent, maintaining normal water balance is achieved by narrowing the diameters of vessels and increasing their number per unit area. The increase in the total area of the pores occurs due to an increase in the number of narrow, single vessels. The quantitative anatomical changes established during the study are adaptive in nature. In the storage parenchyma of wood, there is an increase in the density and linear dimensions of the rays. The volume of the radial parenchyma at a relatively constant average ply value occurs due to an increase in the height of the cells composing the ray. It is noted that sufficient water balance and enrichment of Sorbus aucuparia wood with living cells of the axial and radial parenchyma increases the viability and plasticity of the entire organism, covers the energy costs for reparation processes, and also stimulates the possibility of vegetative reproduction in conditions unfavorable for seed renewal. A significant range of fluctuations in the quantitative characteristics of mountain ash wood elements increases its adaptive capabilities, helping it to occupy a variety of ecological niches in nature, as evidenced by the wide range of this species.