AN INCREASE of THE foliage share in SHOOT phytomass along THE LATITUDINAL GRADIENT AS A COMPENSATORY REACTION OF SCOTS PINE TO A DECREASE IN THE SUM OF EFFECTIVE TEMPERATURES

Behavioral reactions that weaken the limiting influence of abiotic factors play an important role in achieving compliance of plant functioning with the environment. One of such adaptive reactions is the compensation (substitution) of the action of one factor by the influence of an other. It is known that with the deterioration of growing conditions, the proportion of the assimilation apparatus in the total phytomass increases, thereby compensating for its reduced activity in these conditions. In general, an increase in the density of needles on shoots increases the absorption coefficient of photosynthetically active radiation (PhAR) and reflects an increased compensatory ability in unfavorable abiotic conditions. The purpose of our study was to confirm or refute the hypothesis of factor compensation by the example of changes in the share of needles in shoots of Scots pine ( Pinus sylvestris L.) in the gradient of the sum of effective temperatures geographically distributed in Northern Eurasia. Based on the author’s database, which includes 490 definitions of the percentage of needles in the mass of shoots, a regression model of the dependence of needle percentage upon the age, stem diameter and the sum of effective temperatures is constructed, explaining 40 % of the variability of the desired indicator. An inversely proportional dependence of the percentage of needles in shoot phytonass on the sum of effective temperatures has been established. Thus, the hypothesis of compensation of the reduced sum of effective temperatures (and the corresponding PhAR) by an increase in the percentage of needles and the corresponding absorption coefficient of PhAR is confirmed.