Growth, wood chemistry, and fibre length of Norway spruce in a long-term nutrient optimization experiment Seija Kaakinen, Riikka Piispanen, Satu Lehto, Johanna Metsometsa ¨ , Urban Nilsson, Pekka Saranpa ¨a ¨ , Sune Linder, and Elina Vapaavuori Abstract: The study was performed as part of a nutrient optimization experiment at Asa in southern Sweden. The experi- ment was established 1987, in a Norway spruce (Picea abies (L.) Karst.) stand planted in 1975. In the nutrient optimization treatment (IL), all essential macro- and micronutrients were supplied, with irrigation water, every second day during the growing season. In October 2003, nine trees were harvested on both untreated control and IL plots. The IL treatment in- creased annual ring width during the first years of the experiment by ca. 30% and cumulative cross-sectional area 1.5-fold by the end of the experiment. Tracheid length was, however, not affected by the IL treatment. The nitrogen concentration of wood increased and starch concentration decreased as an effect of the IL treatment, suggesting that carbon was allocated to growth rather than storage. The IL treatment increased lignin concentration of wood by 3.4%. Chemical composition varied at different heights along the stem, but with no apparent trend. Re ´sume ´: Cette e ´tude a e ´te ´ re ´alise ´e dans le cadre d’une expe ´rience d’optimisation des nutriments a ` Asa dans le sud de la Sue `de. L’expe ´rience a e ´te ´e ´tablie en 1987, dans un peuplement d’e ´pice ´a commun (Picea abies (L.) Karst. ) plante ´ en 1975. Dans le traitement d’optimisation des nutriments (IL), tous les macro et micro-nutriments essentiels ont e ´te ´ applique ´s dans l’eau d’irrigation a ` tous les deux jours durant la saison de croissance. En octobre 2003, neuf arbres ont e ´te ´ re ´colte ´s dans les parcelles te ´moins non traite ´es et les parcelles IL. Le traitement IL a augmente ´ la largeur du cerne annuel d’environ 30 % durant la premie `re anne ´e de l’expe ´rience et la surface radiale cumulative d’un facteur de 1,5 a ` la fin de l’expe ´rience. La lon- gueur des trache ´ides n’a cependant pas e ´te ´ affecte ´e par le traitement IL. La concentration en azote dans le bois a augmente ´ et la concentration en amidon a diminue ´ sous l’effet du traitement IL indiquant que l’allocation du carbone e ´tait dirige ´ vers la croissance pluto ˆt que l’accumulation de re ´serves. Le traitement IL a augmente ´ de 3,4 % la concentration de la lignine dans le bois. La composition chimique variait selon la hauteur dans la tige mais aucune tendance n’e ´tait apparente. [Traduit par la Re ´daction] Introduction Requirements for higher biomass production of CO 2 neu- tral biofuels (Directive 2003/30/EC 2 ) and development of novel chemical products from wood (e.g., Boudet et al. 2003; Nikinmaa et al. 2007) will necessitate a better under- standing of wood production capacity and of wood material properties. Forest fertilization can be used as an effective sil- vicultural tool to increase biomass production. In the Nordic countries, increases in stem volume growth of forests by fer- tilization are well documented (e.g., Ma ¨lko ¨nen et al. 1990; Tamm 1991; Ingerslev et al. 2001), and in spite of low tem- peratures, stemwood production in the boreal climate could potentially be much greater than it is currently, if water and nutrients are not limiting (cf. Linder 1995; Bergh et al. 1999, 2005). However, increased growth rate is thought to have a nega- tive effect on wood properties for timber and pulpwood, but this may not be true for all wood products. Fibre dimensions and chemical composition of cell walls are genetically deter- mined (Zobel and Jett 1995; Wodzicki 2001), but growth rate, as controlled by environmental conditions and tree age, af- fects wood properties. Fibre properties are related to mechan- ical, physical, and optical properties of end products such as strength, stiffness and performance in use, density, colour, and opacity. Wood density is mainly determined by cell wall thickness and chemical composition, which is also of interest for wood used in biorefineries (Nikinmaa et al. 2007). Horizontal variation is usually the predominant form of within-stem variation of tracheid length and is seen as an in- crease of length from the pith towards the bark (Olesen 1982; Lindstro ¨m 1997). The horizontal variation of tracheid dimensions is caused by the maturation of the cambium (e.g., Helander 1933; Olesen 1977; Saranpa ¨a ¨ et al. 2000) and is controlled by the maturation processes in the apical meri- Received 19 March 2008. Accepted 11 November 2008. Published on the NRC Research Press Web site at cjfr.nrc.ca on 10 February 2009. S. Kaakinen, 1 J. Metsometsa ¨, and E. Vapaavuori. Finnish Forest Research Institute, Suonenjoki Research Unit, Juntintie 154, FI-77600 Suonenjoki, Finland. R. Piispanen, S. Lehto, and P. Saranpa ¨a ¨. Finnish Forest Research Institute, Vantaa Research Centre, P.O. Box 18, FI- 01301 Vantaa, Finland. U. Nilsson and S. Linder. Swedish University of Agricultural Sciences, Southern Swedish Forest Research Centre, P.O. Box 49, SE-230 53 Alnarp, Sweden. 1 Corresponding author (e-mail: Seija.Kaakinen@metla.fi). 2 Directive 2003/30/EC of the European Parliament and of the Council of 8 May 2003 on the promotion of the use of biofuels and other renewable fuels for transport (OJEU L123 of 17 May 2003). 410 Can. J. For. Res. 39: 410–419 (2009) doi:10.1139/X08-180 Published by NRC Research Press