Morphological and physiological changes during leaf ontogeny in genotypes of Eucalyptus young plants

Key message This is a descriptive study on leaf ontogeny, showing the main morphological and physiological changes during development of leaves from young plants in three Eucalyptus genotypes. A descriptive study on key morphological and physiological features during leaf ontogeny in three genotypes-AEC 144, CO 1407 and VCC 865-of Eucalyptus young plants was performed. The work was developed under partially controlled environment, at two stages. First, daily photographing was used aiming at chronologically documenting noticeable changes in leaf ontogeny, such as size, shape and color, to define the reference stages of complete leaf development. Then, a time-varied split plot experiment was carried out to evaluate morphological and physiological changes in genotypes x leaf development stages relationship. The time required for complete leaf formation in Eucalyptus young plants varied at 44-49 days. Throughout this period, changes in leaf size, shape and color allowed us to establish four development stages, hereinafter referred to as A, B, C and D. Morphological features and color looks were described in detail at each leaf development stage. Physiological features, such as dry mass, leaf area, photosynthetic pigment content and photosynthesis rates, were increased throughout leaf development. At the early development stages, the mean values of these features were similar, by comparing the genotypes, but from stage C, however, they became larger in AEC 144 genotype than in CO 1407, which in turn were larger than in VCC 865. Decrease in sucrose hydrolysis by invertases and increase in reducing and soluble sugar content were also found during leaf ontogeny. These biochemical and metabolic changes can be interpreted as evidences of sink-to-source leaf transition, which was consolidated from stage C.