Long‐term exposure of Norway spruce,Picea abies(L.) Karst., to ozone in open top chambers

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Abstract
One clone of spruce, Picea abies (L.) Karst., was exposed to different concentrations of ozone in open-top chambers for three seasons. The treatments were filtered air (CF), non-filtered air (NF) and non-filtered air + ozone (NF +). Changes in ultrastructure occurring in the 1985 flush of needles were followed for three years. Ultrastructural changes due to ozone first occurred in the chloroplasts. A decrease in length of the chloroplasts, an increase of the density of the stroma, and accumulation of ribosome-like granules and a decrease in the size of starch grains, were observed. The second organelle to be affected was the microbody and the last the mitochondria. At this later stage the cytoplasm had also disintegrated. Structural changes always appeared first in the outer cell layer facing the sky. The changes then gradually advanced in the tissue towards the lower part of the needle. In the NF + treatment changes were observed at the first sampling event in November, 1 month after the end of the first exposure period. At this time the needles were about 6 months old. In the NF treatment the same changes appeared when the needles were about 14 months old. No changes were observed in the CF treatment. Changes of the same type as those observed in the mesophyll tissue were also seen in stomatal and endodermal cells. In albuminous cells a general breakdown of the organelles was observed.