Photosynthetic Responses of Aspen Clones to Simultaneous Exposures of Ozone and CO sub(2)

Anticipated increases in tropospheric ozone and carbon dioxide will increase plant stresses. These dynamics were examined in ozone and carbon dioxide experiments on sensitive and tolerant trembling aspen clones. Treatments included exposures over single and three growing seasons. Photosynthetic measurements showed that ozone decreased the photosynthetic rate and stomatal conductance, but increased the leaf senescence. Carbon dioxide increased the photosynthetic rate and lowered stomatal conductance, and increased the negative effects of ozone exposure. The interactions between these processes were further explored.