Cambial activity and seasonal dynamics of xylem and phloem formation (tree ring increment and differentiation of cells) taken from 6 mature trees of Norway spruce (Picea abies (L.) Karst.) growing at a site near Panška reka close to Ljubljana, were monitored. Cross-sections of tissues, prepared from micro-cores, taken weekly in the growing season 2012, were observed under a light microscope and analysed using the image analysis system. The numbers of currently formed xylem, phloem and cambial cells were counted for each sampling, and the widths of the tissues were measured. Cambial activity in 5 Norway spruces started on April 3, 2012 and in 1 spruce a week later. An average completion of cambial cell production lasted 144 days, from August 13 to September 3, 2012. In seasonal formation of xylem tree
rings we found out the first cells in the phase of extension growth, on average on April 17, the first cells in the phase of deposition and lignification of the multilayer secondary cell wall on May 7, while the first fully mature cells were observed on May 24. In seasonal dynamics of phloem ring formation, differentiation of the first cells of early phloem was recorded on March 20, appearance of axial parenchyma on May 2, while the formation of the first cells of late phloem on May 6, 2012. The comparison of xylem and phloem tree rings, formed in the same year, showed that
phloem tree rings were on average 7-8 times narrower than the xylem ones.
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