Response of mature stands of Norway spruce (Picea abies) to boron fertilization Marjoriitta Mo ¨tto ¨nen a,* , Tarja Lehto a , Pedro J. Aphalo a,1 , Mikko Kukkola b , Eino Ma ¨lko ¨nen b a Faculty of Forestry, University of Joensuu, P.O. Box 111, FIN-80101 Joensuu, Finland b Finnish Forest Research Institute, Vantaa Research Centre, P.O. Box 18, FIN-01301 Vantaa, Finland Received 26 March 2002; received in revised form 9 September 2002; accepted 11 November 2002 Abstract The effects of boron (B) fertilizer applied 10 growing seasons earlier were studied in mature Norway spruce (Picea abies (L.) Karst.) trees in long-term factorial fertilization experiments at two field sites. Needle nutrient status, above-ground and below- ground growth and d 13 C and carbon concentrations in the annual rings were measured. Needle B concentrations varied between 4 and 19 mg kg 1 on the plots that had not received B fertilization. On the B-fertilized plots they varied between 15 and 39 mg kg 1 . The lowest B concentrations were on the plots that had received N or NCa fertilization. Needle Mn and Zn concentrations were lower on the B plots than on the plots that had not received B fertilization, although not significantly. Mean annual volume growth was slightly higher on the B plots at the more fertile site, but not at the less fertile one. The living:dead fine root mass ratio and living fine root length were also higher on the B-fertilized plots than on the unfertilized plots, but d 13 C was not significantly affected, suggesting that the water status of the trees was not markedly altered by the increase in root growth. The carbon concentration in the annual rings was higher in the B-fertilized trees than in the unfertilized ones, suggesting the importance of B for wood formation. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Boron; Fertilization; Norway spruce; Root Growth; Volume growth; 13 C 1. Introduction Boron (B) deficiency in forest trees has been reported in many areas worldwide (Stone, 1990; Shorrocks, 1997). In many cases N fertilization has increased the growth of trees and this has led to low or deficient needle B concentrations through a dilution effect, e.g. in stands of Norway spruce (Picea abies (L.) Karst.) and Scots pine (Pinus sylvestris L.) in areas of the Nordic countries where B deposition is low (Aronsson, 1983; Brække, 1983a; Mo ¨ller, 1983). N deposition may induce similar effects on B con- centrations as well as on other micronutrient con- centrations (Ma ¨lko ¨nen et al., 1990). Lowered B concentrations have also been found in Norway spruce trees after liming (Aronsson, 1983; Lipas, 1990; Lehto and Ma ¨lko ¨nen, 1994), and especially, when liming Forest Ecology and Management 180 (2003) 401–412 * Corresponding author. Tel.: þ358-13-251-4423; fax: þ358-13-251-3590. E-mail address: marjoriitta.mottonen@forest.joensuu.fi (M. Mo ¨tto ¨nen). 1 Present address: Department of Biological and Environmental Science, University of Jyva ¨skyla ¨, P.O. Box 35, FIN-40351 Jyva ¨skyla ¨, Finland. 0378-1127/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0378-1127(02)00651-5