PARENT SESSION
Oral Session #5: Ecosystem processes: Decomposition and litter. Presiding: K. Lajtha.
Monday, August 6, 2001. 8:00 AM to 12:15 PM. Hall of Ideas E.

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