Monitoring of xylem formation in Picea abies under drought stress influence

The effect of drought stress on regular cambium activity and wood formation in stems of two different clones of Norway spruce (Picea abies (L.) Karst.) was investigated. Tissue samples were taken during the growing season from May to September 2010. Artificial drought stress, induced by long-term sheltering of the soil, was significantly manifested in clone 15. In the stressed individual, the period of cambium activity was shorter, the total number of formed cells was lower and the resulting tree ring was narrower. The number of cells in the phases of postcambial growth and secondary cell wall formation was significantly lower in comparison to the control tree. The tracheid lignification process was slower in the tree stressed by water deficit and the first mature tracheids were observed later. On the other hand, in clone 18 probably genetic dispositions played an important role as no considerable deviations in the cambium activity and new wood cells production were observed. Fitting xylem increments to the Gompertz function showed that the period of the most intensive cell formation was at the turn of June and July and the maximum daily production of new cells was higher in non-stressed individuals than in the stressed ones. The results of the experiment lead us to the conclusion that drought stress can significantly affect the cambium activity of some clones, the differentiation process of anatomical elements, and thus also the resulting tree ring width.