Summary• Mycosphaerella leaf disease (MLD) is a major cause of foliage damage in Eucalyptus globulus plantations. Our study is the first to describe the physiological effects of MLD on E. globulus leaves. It involved measurements on both field and potted plants.• Changes in photosynthetic parameters in response to MLD were quantified in a study using gas exchange techniques.• There was a negative linear relationship between light-saturated photosynthesis ( A max ) and leaf-level damage from MLD. Reductions in A max were proportionally greater than might be expected from the reduction in green leaf area as a result of the disease, indicating that asymptomatic tissue also was affected by MLD. The reductions in A max were not related to increases in stomatal resistance, but were a result of reduced activity of ribulose bisphosphate carboxylase (Rubisco) and changes in the capacity for ribulose bisphosphate (RuBP) regeneration. Changes in mesophyll resistance to CO 2 were also implicated.• The effect of MLD was similar at different sites and irrespective of tree-level infection, suggesting a general leaf-level response of E. globulus to MLD.
Key words:Eucalyptus globulus , light-saturated photosynthesis ( A max ), maximum rate of Rubisco activity ( V cmax ), Mycosphaerella leaf disease (MLD), potential electron transport rate ( J max ), ribulose bisphosphate carboxylase (Rubisco), ribulose bisphosphate (RuBP), stomatal conductance.
The effects of green pruning on aboveground biomass partitioning and crown architecture were explored in a 3-year-old Eucalyptus nitens (Deane and Maiden) Maiden plantation. Responses were measured in five height zones and three foliage age classes over a 20-month period following removal of 0, 50, or 70% of the green crown length. Development of foliage in the upper crowns of 50%-pruned trees was faster and total leaf area at the end of the experiment was greater than in unpruned trees. Leaf area development of 70%-pruned trees was similar to that of unpruned trees. Larger apical leaves, with a lower specific leaf area (SLA), developed following 50% pruning. However, 70% pruning resulted in smaller leaves, and SLA increased in some crown positions. Pruning reduced branch diameter and length in the upper crowns. However, branches of 50%-pruned trees had an increased ratio of foliage to wood dry mass. These responses to green pruning may have increased the carbon-fixing capacity and the efficiency of carbon utilisation of the remaining crown. Following 50% pruning, responses were sufficient to maintain stem dry mass increment at a level similar to that of unpruned trees. However, following 70% pruning, stem and branch dry mass increment was reduced.Résumé : Les effets de l'élagage des branches vivantes sur la répartition de la biomasse aérienne et l'architecture de la cime ont été étudiés dans une plantation d'Eucalyptus nitens (Deane and Maiden) Maiden âgée de 3 ans. Les réactions ont été mesurées dans cinq zones de hauteur et trois classes d'âge du feuillage sur une période de 20 mois suite à l'enlèvement de 0, 50 ou 70% de la longueur de la cime vivante. Le développement du feuillage dans la partie supérieure de la cime des arbres élagués à 50% était plus rapide et la surface foliaire totale à la fin de l'expérience était plus grande que chez les arbres non élagués. Le développement de la surface foliaire n'était pas différent chez les arbres élagués à 70% et les arbres non élagués. De plus grandes feuilles apicales, avec une plus faible surface foliaire spécifique, se sont développées après un élagage à 50%. Cependant, l'élagage à 70% a entraîné la production de feuilles plus petites et la surface foliaire spécifique a augmenté à certains endroits dans la cime. L'élagage a réduit la longueur et le diamètre des branches dans la partie supérieure de la cime. Cependant, les branches des arbres élagués à 50% avaient un plus fort ratio de la masse sèche des feuilles sur la masse sèche de matière ligneuse. Ces réactions à l'élagage de branches vivantes pourraient avoir augmenté la capacité de fixation du carbone ainsi que l'efficacité de l'utilisation du carbone dans la partie restante de la cime. Chez les arbres élagués à 50%, cela était suffisant pour maintenir l'accroissement en masse sèche de la tige au même niveau que chez les arbres non élagués. Par contre, après un élagage à 70%, l'accroissement en masse sèche des branches et de la tige était réduit.[Traduit par la Rédaction] Pinkard and Beadle 1428
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