Seasonal dynamics of phloem formation in Silver fir and Norway spruce as affected by drought

Jožica Gričar and Katarina Čufar (2008) Seasonal dynamics of phloem formation in Silver fir and Norway spruce as affected by drought. Russian journal of plant physiology, 55 (4). pp. 538-543. ISSN 1021-4437

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Abstract

The dynamics of phloem growth ring formation in silver fir (Abies alba Mill.) and Norway spruce (Picea abies Karst.) at different sites in Slovenia during the droughty growing season of 2003 was studied. We also determined the timing of cambial activity, xylem and phloem formation, and counted the number of cells in the completed phloem and xylem growth rings. Light microscopy of cross-sections revealed that cambial activity started on the phloem and xylem side simultaneously at all 3 plots. However, prior to this, 1-2 layers of phloem derivatives near the cambium differentiated without previous divisions.The structure of the early phloem was similar in silver fir and Norway spruce. Differences in the number of late phloem cells were found among sites. Phloem growth rings were the widest in Norway spruce growing at the lowland site. In all investigated trees, the cambium produced 5-12 times more xylem cells than phloem ones. In addition, the variability in the number of cells in the 2003 growth ring around the stem circumference of the same tree and among different trees was higher on the xylem side than on the phloem side. Phloem formation is presumably less dependent on environmental factors but is more internally driven than xylem formation.

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