PROCEEDINGS: Index of Abstracts
INTERACTING EFFECTS OF OZONE AND CO2 ON GROWTH AND
PHYSIOLOGICAL PROCESSES IN NORTHERN FOREST TREES
1-USDA Forest Service, North Central Forest Experiment
Station, Rhinelander, WI 54501. 2-School of Forestry, Michigan Tech
University, Houghton, MI 49931.
Globally, surface-level concentrations of both CO2 and ozone (O3)
are increasing annually. Because many studies have shown beneficial
effects of increasing CO2, predictions have been made that elevated
levels of CO2 would compensate for growth decreases caused by O3.
For the past two years, we have been examining the interaction of
O3 and CO2 on trembling aspen (Populus tremuloides) and eastern
white pine (Pinus strobus) in open-top chamber studies involving
both plants in pots and plants growing in the ground.
After two seasons of exposure to elevated ozone, alone or in combination
with elevated CO2 (ambient plus 150 ppm), soil-grown aspen and eastern
white pine trees are exhibiting different response. While neither
of the two pine seed sources has been negatively affected by ozone,
significant negative effects of O3 have been found for two aspen
clones differing in O3 tolerance: The negative impact of ozone was
not compensated by CO2 and for some physiological responses such
as photosynthesis, stomatal conductance, chlorophyll content and
leaf abscission, a significant negative interaction has been demonstrated
for O3 plus CO2 treatment. Second-year growth and biomass measurements
appear to be following our physiological measurements. Crown architecture
has also been altered by the O3 and CO2 combination.
In addition, elevated CO2 appears to alter the sensitivity of the
tolerant aspen clone, making it more sensitive to O3, as determined
both by gas exchange and biomass.