Effects of Melampsora leaf rust disease and chronic ozone exposure on poplar

The combined and separate impacts of Melampsora sp. infection and chronic O3 (100 nl l-1, 8 h per day, for 17 days) on poplar health (Populus trichocarpa T&G×Populus balsamifera Duroi non L.), were assessed in a closed chamber fumigation experiment. Incidence and severity of Melampsora infection was increased significantly by O3. Comparisons with non-infected control plants showed that Melampsora and O3 alone had a minor impact on tree health, although their combined effect was severe. By day 17, O3 had significantly increased leaf injury and the percentage of senescing leaves. Melampsora significantly reduced stem height throughout the exposure. Melampsora infection and O3 together substantially increased leaf injury and significantly decreased stem height and biomass, live leaf and total leaf biomass plus whole shoot biomass. They also significantly decreased the area of upper leaves and the ratio of stem weight/stem length, but increased significantly both leaf weight/stem weight and leaf number/leaf weight ratios.