Photosynthetic response to ozone of two poplar clones showing different sensitivity

The mature leaves of two clones of poplar were fumigated with 150 ppb of ozone for 5 h. In both clones a strong reduction in photosynthetic activity was observed, but the kind of the response appeared to the different. The resistant clone showed an effect at both stomatal and mesophyllic levels and this appeared to be a consequence of regulatory mechanisms more than effects of O3 injury. A rapid recovery of photosynthetic ability was observed when the ozone was removed. The sensitive clone appeared not to be able to undergo this regulatory sequence, so the effects of ozone were stronger and not reversible.