Gricar J., Cufar K*., Zupancic M., Straze A., Oven, P.: University of Ljubljana, Biotechnical Faculty, Department of Wood Science and Technology, Rozna dolina, Cesta VIII/34, SI-1000 Ljubljana, Slovania – A pinning and intact tissue sampling method for research into wood formation in Norway spruce (paper)
            The objectives of our research were to study xylem growth ring formation in Norway spruce (Picea abies) with pinning method (PM) and intact tissue sampling method (ITSM), and to compare methods. Experiments were done on dominant and co-dominant trees growing at two elevations in Slovania (359 m and 1200 m) in the 2003 growing season. Weekly increment was examined on transverse sections under a light microscope. Wounding of the cambium with a pin caused desiccation of differentiated xylem, necrosis of undifferentiated cells, formation of callus, traumatic resin canals and wound-wood. Cell counting and cell measurements were difficult in cases when tissue under callus was crushed and torn or when cambial cells and tracheids in postcambial growth were not preserved in callus. Calculating of relative increments was easy because the entire annual xylem growth ring was included in PM samples. The main advantage of PM was in preserving information on seasonal dynamics of xylem formation in the xylem growth ring for many years after the experiment. Sampling of intact tissue represented a critical part of ITSM, especially at the height of the growing season when the wide cambial region was sensitive to mechanical rupture. Difficulties with sampling might appear in trees with a very thick rhytidome. ITSM was found to be suitable for studying seasonal dynamics of individual phases of xylogenesis. Well preserved differentiating cells including cambial cells were easy to define under the light microscope with polarized light. Using the ITSM method, there was no need to fell trees at the end of the experiment. Onset and cessation of divisional activity of cambium was distinct with ITSM. With PM, termination of cambial activity could be masked with reactivation of cambium due to pinning. Since both methods show similar results, we concluded that ITSM and PM are suitable for studying development of xylem rings.