Leaf Orientation in Juvenile Eucalyptus camaldulensis

Abstract

Leaves of six genotypes of Eucalyptus camaldulensis Dehnh. from five Australian locations were compared. The juvenile plants were approximately 6 months old, an age related to field planting times in salinised and waterlogged agricultural catchments. The leaves of juvenile plants of Eucalyptus camaldulensis do not exhibit solar-tracking, but leaf orientation is believed to maximise solar radiation absorption. Through vertically-tilted leaves and rotated leaf blade orientation, replicate clonal plantlets from Erudina, SA, potentially absorbed at mid-morning, mid-day and mid-afternoon, an average of 71%, 15% and 74%, respectively, more photosynthetically active radiation than a theoretical plant with horizontal, non-self shading leaves during spring. This clone intercepted, on average, between 67% and 76% of all the solar radiation potentially intercepted if all leaf blades faced the sun throughout the day and no leaf shading occurred. Clonal plantlets from Silverton, NSW, and Dongara, WA, also displayed leaf orientations that showed greater radiation interception compared to a theoretical plant with horizontal leaves. Two genotypes from Wooramel, WA, and a genotype from Murray Bridge, SA, showed a 13-24% reduction in interception in the middle of the day compared to the theoretical plant with all horizontal and non-shading leaves, but 15-96% more radiation during the morning and evening through leaf orientation. Morphological and anatomical leaf characteristics of these clones tended to show characteristics typical of 'sun-leaves', or leaves developed under high light conditions. The Erudina, SA, and Silverton, NSW, clones, having the greatest potential light interception through leaf orientation, produced leaves with a more glaucous, light-reflective surface. Glaucescence may protect against too much light being absorbed by the leaves of these clones. Variation in the degree of orientation of leaves in these six genotypes of E. camaldulensis indicates that it could be possible to select clones which maximise energy utilisation during periods of lower light availability and, hence, have enhanced growth and survival in early stages of establishment.