© 2001 Heron Publishing—Victoria, Canada
Nitrogen availability modifies the ozone responses of Scots pine seedlings exposed in an open-field system
Jarkko Utriainen (1, 2) and Toini Holopainen (1)
1. Department of Ecology and Environmental Science, University of Kuopio, P.O. Box 1627, FIN-70211 Kuopio, Finland / 2. Department of Environmental and Natural Resource Science, Faculty of Agriculture, Tokyo University of Agriculture and Technology,
Fuchu, Tokyo 183-8509, Japan / Received March 5, 2001
Summary
Three-year-old Scots pine (Pinus sylvestris L.) seedlings were exposed to either ambient or elevated (1.5–1.6 × ambient) ozone concentration ([O3]) for three growing seasons in an open-field fumigation facility where they were irrigated during the growing season with
a nutrient solution providing nitrogen (N) at 70 (LN treatment), 100 (control) or 150% (HN treatment) of the optimum supply
rate. Treatment effects were most evident during the third year of exposure, when the ambient [O3] + HN treatment enhanced whole-plant biomass, root/shoot dry weight ratio, needle pigment concentrations and the number of
chloroplast plastoglobuli in the mesophyll cells in current-year (C) needles, whereas it reduced starch accumulation in C
needles and abscission of 2-year-old (C+2) needles. In the control fertilization, 3 years of exposure to elevated [O3] decreased stem-base diameter and increased K concentration and electron density of chloroplast stroma in C needles. Plants
in the HN treatment exposed for 3 years to elevated [O3] had significantly lower heights, current-year main shoot length and root/shoot dry mass ratio than control plants, and increased
abscission of C+2 needles. In contrast, O3-induced changes in the ultrastructure of mesophyll cells were most evident in seedlings grown for 3 years in the LN treatment.
We conclude that, in Scots pine, a relatively O3-tolerant species, chronic O3 exposure leads to cumulative growth reduction, increased needle abscission and changes in carbon allocation that are strongly
influenced by plant N availability.
Keywords:
elevated O3, growth, Ingestad, nutrient availability, nutrient concentrations, pigment concentrations, Pinus sylvestris, starch concentrations, ultrastructure.
