This experiment was conducted during the four seasons: Spring, summer, autumn and winter of two successive annual cycles; 2008/2009 and 2009/2010 (starting from May 2008). Four Eucalyptus species were under investigation; Eucalyptus camaldulensis Dehnh., Eucalyptus cinerea F. Muell. ex Bentham, Eucalyptus citriodora Hook. and Eucalyptus globulus Labill. Seasonal variations in the amount of fixed and volatile oils in Eucalyptus spp. matured leaves were investigated. It was determined that the amount of total lipids and essential oils significantly varied by the seasons (P < 0.01). The amount of total lipids in Eucalyptus spp. reached its peak mostly in spring. But the amounts of essential oils in different species were determined to be higher in summer, autumn and spring seasons, than in winter. Furthermore, the amount of total lipids and essential oils was higher in E. camaldulensis and E. cinerea than in other species. The anatomical investigation in the four studied Eucalyptus species, in relation to lipids percentage indicated that, the best lipids percentage amounts in this study were exhibited in E. cinerea and E. camaldulensis, for spring and winter; and were in agreement with these species highest lamina thickness. In general, fluctuation in lipids percentage is more correlated to the internal structure of lamina (duct average diameter, ducts total numbers, and open ducts numbers) in the same season; whereas, among seasons, it is thought that metabolism contributed more greatly. Cuticle thickness is true correspondence to seasonal environmental fluctuation, since it increases in all species, by shifting up from spring to summer then decrease to winter. Essential oils secretion which coincided with lipids percentage may be due to environmental stress influence over metabolism rather than structural adaptation.
Key words: Eucalyptus, seasons, fixed and volatile oils, lamina, anatomy, glands.
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