© 2005 Heron Publishing—Victoria, Canada
Leaf photosynthetic characteristics of silver birch during three years of exposure to elevated concentrations of CO2 and O3 in the field
Johanna Riikonen (1, 2), Toini Holopainen (1), Elina Oksanen (1) and Elina Vapaavuori (2, 3)
1. Department of Ecology and Environmental Science, University of Kuopio, P.O. Box 1627, 70211 Kuopio, Finland / 2. Finnish Forest Research Institute, Suonenjoki Research Station, Juntintie 154, FIN-77600 Suonenjoki, Finland / 3. Corresponding author (elina.vapaavuori@metla.fi) / Received July 2, 2004; accepted October 10, 2004; published online March 1, 2005
Summary
Effects of elevated concentrations of carbon dioxide ([CO2]) and ozone ([O3]) on photosynthesis and related biochemistry of two European silver birch (Betula pendula Roth) clones were studied under field conditions during 1999–2001. Seven-year-old trees of Clones 4 and 80 were exposed for
3 years to the following treatments in an open-top chamber experiment: outside control (OC), chamber control (CC), 2× ambient
[CO2] (EC), 2× ambient [O3] (EO) and 2× ambient [CO2] + 2× ambient [O3] (EC+EO). During the experiment, gas exchange, chlorophyll fluorescence, amount and activity of Rubisco, concentrations of
chlorophyll, soluble protein, soluble sugars, starch, nitrogen (N) and carbon:nitrogen (C:N) ratio were determined in short-
and long-shoot leaves. Elevated [CO2] increased photosynthetic rate by around 30% when measurements were made at the growth [CO2]. When measured at ambient [CO2], photosynthesis was around 15% lower in EC trees than in CC trees. This was related to a ~10% decrease in total leaf N,
to 26 and 20% decreases in the amount and activity of Rubisco, respectively, and to a 49% increase in starch concentration
in elevated [CO2]. Elevated [O3] had no significant effect on gas exchange parameters and its effect on biochemistry was small in both clones. However, elevated
[O3] decreased the proportion of Rubisco in total soluble proteins and the apparent quantum yield of photosystem II (PSII) photochemistry
in light and increased non-photochemical quenching in 2000. The interactive effect of CO2 and O3 was variable. Elevated [O3] decreased chlorophyll concentration only in EO trees, and the EC+EO treatment decreased the total activity of Rubisco and
increased the C:N ratio more than the EO treatment alone. The small effect of elevated [O3] on photosynthesis indicates that these young silver birches were fairly tolerant to annual [O3] exposures that were 2–3 times higher than the AOT40 value of 10 ppm.h. set as a critical dose for forest trees.
Keywords:
Betula pendula, chlorophyll, clone, field experiment, fluorescence, gas exchange, nitrogen, open-top chamber, Rubisco.
