Cell ultrastructure of needles from saplings of Norway spruce, Picea abies (L) Karst., exposed to ozone and low phosphorus supply in open-top chambers

Two-year-old saplings of one clone of Norway spruce, Picea abies (L.) Karst., were exposed to ozone in open-top chambers. The treatments were; charcoal filtered air (CF); non-filtered air + 1.5 times ambient ozone (NF+); charcoal filtered air and low phosphorus supply (CF/PD); non-filtered air + ozone and low phosphorus supply (NF+/PD). Ozone exposure was started in 1992 and low phosphorus supply in 1993. Current (C) and 1-year-old (C+1) needles were sampled on 27 July 1994 for structural studies. Electron microscopy showed that the structure of the mesophyll cells in C and C+1 needles from CF treatment was intact. Statistically significant ozone-induced changes in ultrastructure were found only in the chloroplasts, all the other organelles were intact. In both ozone treatments the stroma was granulated. The granules were about 1.5 times the size of the chloroplast ribosomes. In the low phosphorus supply changes were seen in the chloroplasts, in the mitochondria, and in the cytoplasm. The mean chloroplast and starch grain areas were significantly increased. In both age classes about 12% and 20% of the mitochondria were injured in the CF/PD and NF+/PD treatments, respectively. Furthermore, the cytoplasm in the C needles from low phosphorus supply treatments was partly disintegrated. The symptoms induced by ozone and low phosphorus supply were clearly distinguishable from each other, also in combined treatments, which points out their diagnostic values.