Influence of ozone and soil nitrogen content on the stem anatomy of Norway spruce saplings grown in open-top chambers

Four-year-old Norway spruce saplings (Picea abies) were exposed to different concentrations of ozone in open-top chambers for 22 weeks. The treatments were charcoal filtered air (CF), non-filtered ambient air (NF) and two elevated ozone treatments: non-filtered air with O-3, added at 25 nl l(-1) (NF25) and at 50 nl l(-1) (NF50). In each chamber, half of the investigated saplings were grown on nitrogen-poor soil (17 mg N kg(-1)) and half on nitrogen-enriched soil (34 mg N kg(-1)). Changes in the anatomy of the stem, the growth parameters, and nitrogen concentration in needles and stem were followed over one growing season. In saplings grown on nitrogen-enriched soil the number of tracheids and the number of latewood tracheids decreased, but diameter of latewood tracheids increased with increasing ozone concentration in comparison to ambient level of ozone. In the fumigated saplings grown on nitrogen-poor soil, the number of sieve cells and diameter of latewood tracheids decreased with increasing ozone concentration in comparison to ambient level of ozone. Ozone increased the thickness of sieve cell walls independent of the nitrogen level in the soil. Needle length was the only growth parameter that was very little reduced after one growing season of combined nitrogen-enriched soil and fumigation with high ozone concentrations. Foliar and stem nitrogen concentrations did not respond significantly to increased ozone levels. (C) 1998 Elsevier Science B.V. All rights reserved.