Rhythms in the Seasonal Dynamics of Apical Growth of Stem and Branches of Scotch Pine Trees (Pinus sylvestris L.)

This article studies the manifestations of rhythm in the seasonal dynamics of apical growth of stems and axial shoots of Scotch pine trees growing in areas with different forest growth conditions (forest cultures and natural regeneration under the canopy) in a forest park in Yekaterinburg. The analysis is carried out based on a comprehensive quantitative approach to the study of morphogenesis, including a comparison of morphometric and physiological data. Four stages lasting 1–4 weeks are distinguished in seasonal changes in growth characteristics. The seasonal dynamics of the growth rate is nonlinear, and accelerations are oscillatory. The period of acceleration oscillations is about 1 week, which corresponds to infradian rhythms. The amplitudes of acceleration oscillations and the growth rate increase at the first two stages, and they decrease at the stages of additional and complete growth. It is found that the general appearance of the seasonal dynamics of growth rates and accelerations of stem and branches is similar. The differences between them are in the discrepancy between the start and end dates of individual growth stages, as well as in higher rate of stem growth. It is found that a decrease in the influx of assimilates and reserve substances into the apical part of the stem by removing branches of the two upper tiers of the crown leads to a decrease in the stem growth rate, but does not change its seasonal dynamics. It is found that seasonal changes in the stem and branch growth rate in Scotch pine correlate with air temperature more strongly than in previously studied species. No connection is found between growth acceleration and air temperature. The features of stem and branch growth indicate that the morphogenetic processes in them are of a similar nature.