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Populus tremuloides and Betula papyrifera decomposition under independent and interactive effects of elevated CO2 and O3.
Parsons, William 1, Lindroth, Richard1, Bockheim, James1, 1
ABSTRACT- Elevated CO2 concentrations are known to alter plant growth and decomposition, but little is known how enrichment with multiple atmospheric pollutants (including CO2) will affect these processes. In this study, leaves of aspen (Populus tremuloides) and paper birch (Betula papyrifera) were grown and decomposed under ambient CO2 + O3 (Control), elevated CO2 (ambient+200 L L-1), elevated O3 (1.5 x ambient), or elevated CO2 + O3 at the Aspen-FACE (Free-Air CO2 and O3 Enrichment) array in northern Wisconsin. Leaf litter was placed in mesh bags, which were redeployed in the treatments and removed at 1, 4, 6, 8 and 12 mo intervals. Our hypothesis for both species was supported that 1-year decay rates would differ from controls when litter was produced under high CO2 or O3. As predicted, low quality litter (high C:N) produced in elevated CO2 decayed more slowly than litter from control plots, while O3 exposure yielded better quality litter (low C:N), which decayed more rapidly than controls. Responses to elevated CO2+O3 could not be predicted from either gas alone. Overall, birch decayed 5-10% faster than aspen. Non-additive or counter-intuitive effects of multiple trace gas additions must be considered in future carbon transfer and storage experiments.
KEY WORDS: populus tremuloides, betula papyrifera, decomposition, aspen-face