Intra-annual tracheid formation of Norway spruce provenances in southern Finland |
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Authors: | Tuomo Kalliokoski Mehedi Reza Tuula Jyske Harri M?kinen and Pekka N?jd |
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Institution: | (1) Southern Finland Regional Unit, Finnish Forest Research Institute, P.O. BOX 18, 01301 Vantaa, Finland;(2) Department of Forest Sciences, University of Helsinki, P.O. BOX 27, 00014 Helsinki, Finland;(3) School of Science and Technology, Aalto University, P.O. BOX 11000, 00076 Aalto, Finland |
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Abstract: | We studied the intra-annual wood formation in a Norway spruce provenance experiment in southern Finland from 2004–2008. Two
Finnish provenances, northern and southern, as well as German and Hungarian provenances were included. Timing of tracheid
formation and differentiation, and tracheid dimensions were determined from periodically extracted microcores. The aim was
to determine the differences between the years and provenances in the timing of the xylogenesis and in the xylem characteristics.
Year-to-year variation was high both in timing of tracheid formation and xylem characteristics, while between-provenance differences
were small. The onset of tracheid formation varied from early May to late June in different trees in different years. The
onset of tracheid formation was not closely related to the annual variations of temperature sum. In all the years, daily temperatures
exceeded the threshold +5°C for several weeks before the onset of tracheid formation. The highest tracheid formation rate
occurred after the summer solstice in all years and generally coincided with the highest daily temperatures during the growing
season. Tracheid production ceased early in 2006 due to a mid-summer drought. Cell differentiation continued late in autumn
as non-mature tracheids were still observed around mid-September. No clear differences between the provenances in the timing
of tracheid formation were observed, although the Finnish provenances tended to initiate tracheid formation slightly earlier
than the other provenances. The tree-ring widths of the Finnish provenances were also wider, while tracheid diameter of the
German provenance was slightly smaller. Our results indicate that between-tree variation in the timing of wood formation is
high compared with the latitude effect of seed source. |
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