Phloem- and xylogenesis in Scots pine stems in the post-fire period

Abstract

The influence of natural ground fire of varying intensity on the growth processes in the stems of Scotch pine (Pinus sylvestris L.) trees growing in the Krasnoyarsk forest-steppe was studied. The primary reaction is the decrease in the number of cells in the zones responsible for the formation and development of phloem and xylem cells – cambium, growth by expansion, secondary wall thickening – with increasing in the impact degree of the stem by fire. Thermal impact causes the decrease in moisture in the developing layers of phloem and xylem. These changes in the conditions of cell morphogenesis lead to a decrease in the number of cells produced by the cambium towards the phloem and early xylem tracheids. In the post-fire period, the structure of transport routes (width of rays and their content in tissues), which provide the supply of photoassimilates to developing tissues, changes. The width of the rays in the phloem and xylem increases. The content of rays in the xylem also increases with the degree of impact. In the phloem, the content of rays increases with an average degree of stem damage and decreases with an increase in the degree of damage. At the same time, the content of axial parenchyma in the phloem increases. In the radial and axial parenchyma of the inner bark the content of starch, being reserve pool of carbohydrates for growth processes, varies depending on the degree of exposure to fire on the stems. At the end of the growth season, the number of cells in the formed layer of conductive phloem decreases with increasing in the degree of fire damage to the stem. The volume of the ray system (width of ray and their content), on the contrary, increases significantly with increasing fire impact. In the xylem, as a result of fire exposure, fewer early and late tracheids are formed, their sizes decrease, and the amount of biomass accumulated in the cell walls decreases. In October, after the end of growth processes, there is no starch in the radial and axial parenchyma of the inner cortex.

Keywords

• pinus sylvestris l.
• ground fire
• xylem
• phloem
• structure
• cells