© 1996 Heron Publishing—Victoria, Canada
Growth responses and related biochemical and ultrastructural changes of the photosynthetic apparatus in birch (Betula pendula) saplings exposed to low concentrations of ozone
E. Pääkkönen (1), J. Vahala (2), T. Holopainen (1), R. Karjalainen (2) and L. Kärenlampi (1)
1. Department of Ecology and Environmental Science, University of Kuopio, P.O. Box 1627, 70211 Kuopio, Finland / 2. Department of Plant Biology, Plant and Forest Pathology Section, University of Helsinki, 00014 Helsinki, Finland / Received July 25, 1995
Summary
Saplings of ozone-sensitive and ozone-tolerant birch (Betula pendula Roth.), clones B and C, respectively, were exposed to ozone concentrations that were 1.7-fold higher than ambient for one
growing season under open-field conditions. Ambient air was used as the control treatment. In the ozone-sensitive clone B,
there was an initial stimulation of leaf area growth in response to the ozone treatment, but further ozone exposure caused
reductions in leaf and stem biomass growth, Rubisco and chlorophyll a contents, net photosynthesis, water use efficiency and
chloroplast size. It also caused an alteration in chloroplast shape and injury to thylakoid membranes. In the ozone-tolerant
clone C, ozone fumigation did not affect growth rate, and there were no consistent changes in chlorophyll content, photosynthesis
or water use efficiency. There were also fewer ultrastructural abnormalities in the chloroplasts of clone C than of clone
B. Based on the observed biochemical, physiological and structural changes in chloroplasts of clone B in response to low concentrations
of ozone, we conclude that the increasing concentration of tropospheric ozone represents a risk to natural birch populations.
Keywords:
Betula pendula, growth ultrastructure, ozone, photosynthetic machinery.
