Exposure of cottonwood plants to ozone alters subsequent leaf decomposition.

Cottonwood saplings were exposed to ozone or charcoal-filtered air in a closed chamber. After leaf abscission, decomposition of individual leaf discs was measured in containers of stream water. Exposure of plants to 200 ppb ozone for 5 h caused early leaf abscission and changes in the chemical composition of leaves at time of abscission. Early-abscised leaves from O3-exposed plants had higher nitrogen, but decomposed more slowly than leaves from control plants. Leaves from O3-exposed plants that abscised at the normal time had lower nitrogen content and lower specific leaf mass than control leaves, but decomposed at the same rate as leaves from control plants. The results imply that O3 exposure can alter fundamental processes important to the functioning of detritus-based aquatic ecosystems.