The structure and development of Siberian stone pine (Pinus sibirica Du Tour) elementary shoot

The aim of this study was to analyze the structure of the elementary shoot using the example of major axes of the first-order branches from the female crown layer as the most highly organized and the most important for the crown formation. We examined information on Siberian stone pine (Pinus sibirica Du Tour) elementary vegetative shoot structure with adaptive significance and formation mechanism of various morphological elements. The material was collected in three so called villageside (thinned) Siberian stone pine forests: the first (100-110 years old) was located in the lower part of the forest belt of the North-Eastern Altai. The second (70-80 years) and the third (160-170 years) were located in the southern taiga subzone of the Western Siberian plain (the South-East of Tomsk oblast). 10 co-dominant trees were taken from each of the forests. 5 branches were taken of the upper part of the crown from each tree. We registered the morphological structure of the last 10 annual shoots, i.e. the number and sequence of different types of stem units was fixed. The most characteristic trait is pronounced acropetal gradient of lateral organs size. The gradient was apparent only in the presence and size of axillary structure "axial component". In the direction of proximal to distal shoot pole, sterile cataphylls gave place to fertile ones; small and simple axillary structures gave place to large and compound ones: short shoots → latent buds → lateral long shoots → seed cones. The length of lateral long shoots increased several times with increasing their sequence number at the genetic spiral of axial shoot almost exclusively due to the number of stem units. Consequently, the differences between them were mainly set at the stage of lateral buds formation. The dependence of the cones structure and development from their position at the genetic spiral of axial shoot appeared principally in that fact that the first cone aborted many times more often than the rest. All living cones (including the first one, if not aborted) were surprisingly uniform by size and other features. If we express the results of axillary meristem activity in terms of some generalized index, which characterized the axillary structures presence, size, and complexity; then the change of the index was "approximated" as S-shape curve with long exponential and short logarithmic "branches": along the whole sterile zone and the most part of fertile zone, the index increased very slowly (majority of short shoots); then it increased more and more quickly (the last short shoots and dormant buds); then it increased again slowly (lateral long shoots); and at last it stabilized (seed cone). Acknowledgments: This work was partially supported by the Siberian Branch of the Russian Academy of Sciences, Basic Grant № VI.52.2.6. and Interdisciplinary Integration Grant № 140. The article contains 2 figures, 2 tables, 33 ref.

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