Title : Annual ring formation in Scots pine stems as the reaction on seasonal changes in photosynthesis and respiration
Abstract:
Annual wood increment formation in Scots pine stems was studied simultaneously with the photosynthetic activity of tree crown and stem respiration, steaming of newly formed and the maintenance of living tissue. The formation of annual wood layer was evaluated as the production of xylem and phloem cells by cambium and as biomass accumulation in separate periods of the season. With this purpose the number of the cells, produced by cambium, and morphological parameters of tracheids were estimated at cross-sections of the cores, knocked out of the trunks through 7-11 days during vegetation. In each of the days of observation period photosynthesis and respiration of the trunk were registered, the data were summarized and divided into the day of this period. Additionally the respiration of growth and maintenance were considered. All calculations were carried out for whole season vegetation and separate periods of the season. Photosynthesis influenced the cambium production of phloem cells mainly in May-June whereas of xylem cells in May-June and August. Temperature positively influenced xylem cell formation, but the level of dependence changed in different season periods. Most active cambium initials were divided in the direction of xylem at a temperature of no higher than 20° C. Phloem cells formation by cambium during vegetation showed a negative relationship with temperature and optimal temperature for that was not higher than 15°C. But in each of the periods the values of optimum changed because of a variation of other external factors. Reduced soil moisture store, lack of rainfall and increasing temperatures in July adversely affected the activity of cambium. Cambium activity didn't show any dependence with the overall cost of respiration throughout the season, but xylem cell production in certain periods had a significant positive correlation with growth respiration and maintenance respiration. Cambium produced the cells of xylem or phloem with different degrees of their relationships with respiratory process.
According to data on tracheid wall cross-section area increment the principal amount of annual ring biomass was accumulated twice in the season – in May-June and in August. In those periods the biomass deposition had very high connection with photosynthesis as the source of substrates for biosynthesis of cell wall components due to favorable temperature and moisture. In July biomass deposition decreased significantly since the temperature higher 23? ? suppressed photosynthesis. The connections between biomass deposition and growth respiration as well maintenance respiration were practically rectilinear in May-June. In July because of high temperature the biomass deposition had direct correlation with maintaining respiration whereas the connection with growth respiration was absent. In August due to temperature declining and the intensification of photosynthesis the biomass accumulation was enlarged. Simultaneously growth respiration increased with diminution of maintenance respiration.
The coherence of cambial activity and biomass accumulation in xylem cell walls with weather conditions of separate periods, as well as with photosynthesis, growth respiration and maintenance respiration has been found to be described more adequately by the second order equations. This allows finding out optimal conditions of physiological processes, in which the production of cells by cambium and accumulation of substances in cell walls occurs.
