AOBPreview originally published online on August 27, 2004
Annals of Botany 2004 94(4):623-634; doi:10.1093/aob/mch182
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Annals of Botany 94/4, © Annals of Botany Company 2004; all rights reserved
Ozone Effects on the Ultrastructure of Peatland Plants: Sphagnum Mosses, Vaccinium oxycoccus, Andromeda polifolia and Eriophorum vaginatum
Department of Ecology and Environmental Science, University of Kuopio, PO Box 1627, FIN-70211 Kuopio, Finland
* For correspondence at: Institute of Biology, Department of Terrestrial Ecology, University of Copenhagen, Oester Farimagsgade 2D, DK-1353 Copenhagen K, Denmark. E-mail Riikka.Rinnan{at}uku.fi
Received: 24 February 2004 Returned for revision: 16 April 2004 Accepted: 5 July 2004 Published electronically: 27 August 2004
• Background and Aims Ozone effects on peatland vegetation are poorly understood. Since stress responses are often first visible in cell ultrastructure, electron microscopy was used to assess the sensitivity of common peatland plants to elevated ozone concentrations.
• Methods Three moss species (Sphagnum angustifolium, S. magellanicum and S. papillosum), a graminoid (Eriophorum vaginatum) and two dwarf shrubs (Vaccinium oxycoccus and Andromeda polifolia), all growing within an intact canopy on peat monoliths, were exposed to a concentration of 0, 50, 100 or 150 ppb ozone in two separate growth chamber experiments simulating either summer or autumn conditions in central Finland. After a 4- or 5-week-long exposure, samples were photographed in a transmission electron microscope and analysed quantitatively using image processing software.
• Key Results In the chlorophyllose cells of the Sphagnum moss leaves from the capitulum, ozone exposure led to a decrease in chloroplast area and in granum stack thickness and various changes in plastoglobuli and cell wall thickness, depending on the species and the experiment. In E. vaginatum, ozone exposure significantly reduced chloroplast cross-sectional areas and the amount of starch, whereas there were no clear changes in the plastoglobuli. In the dwarf shrubs, ozone induced thickening of the cell wall and an increase in the size of plastoglobuli under summer conditions. In contrast, under autumn conditions the cell wall thickness remained unchanged but ozone exposure led to a transient increase in the chloroplast and starch areas, and in the number and size of plastoglobuli.
• Conclusions Ozone responses in the Sphagnum mosses were comparable to typical ozone stress symptoms of higher plants, and indicated sensitivity especially in S. angustifolium. The responses in the dwarf shrubs suggest stimulation of photosynthesis by low ozone concentrations and ozone sensitivity only under cool autumn conditions.
Key words: Andromeda polifolia, electron microscopy, Eriophorum vaginatum, ozone, peatland, Sphagnum, ultrastructure, TEM, Vaccinium oxycoccus