Radial ring width and wood structure in the ozone-exposed Norway spruce seedlings grown under different nitrogen regimes

Norway spruce seedlings were exposed to two ozone levels (ambient and 1.5-1.6 x ambient) at moderate (optimum N), low (70% of optimum N), and high soil-nitrogen availability (150% of optimum N), in an open-air exposure field for two growing seasons. Radial ring width and wood structure in the stem were investigated from the seedlings. The seedlings grown under elevated 03 showed an increase in radial width of growth ring built during the first exposure season. Elevated 03 increased latewood width, its proportion within the growth rings being most pronounced in low N treated trees, whereas higher N mitigated latewood production. High soil N increased earlywood width and resulted in an increased lumen area and lower cell-wall/cell-lumen ratio of tracheids within earlywood and latewood. Ozone had no effect on earlywood width or the lumen area or cell wall/ cell lumen ratio in juvenile wood. High latewood percentage in O-3-exposed seedlings implies earlier transition from earlywood to latewood or longer period of latewood formation.