Autumn Revival of Summer Leaves in the Seasonal Dimorphic, Drought Semi-Deciduous Mediterranean Shrub Phlomis-Fruticosa L
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Kyparissis, A.
(EN)
Πανεπιστήμιο Ιωαννίνων. Σχολή Επιστημών και Τεχνολογιών. Τμήμα Βιολογικών Εφαρμογών και Τεχνολογιών
(EL)
Kyparissis, A.
(EN)
Morphological and physiological characteristics of summer leaves from the drought semi-deciduous, seasonal dimorphic, Mediterranean shrub Phlomis fruticosa L. were followed from mid-July until the time of shedding. Leaf growth and photosynthetic metabolism during the summer were arrested, while relative water content fell to extremely low values. Immediately after the first heavy rains of October, summer leaves, instead of being replaced by winter leaves as was previously thought, were released from dormancy and leaf size, photosynthetic rate and pigment content increased considerably in parallel with relative water content, to reach the final values within one month. During this period, protein content per unit leaf area remained unchanged. Analysis of changes in leaf size, dry weight per leaf and specific leaf mass revealed that a considerable part of leaf growth was simply related to water absorption. Indeed, saturation of cut summer leaves with water at their light compensation point, resulted in the increase of their size by 55 % in 24 hours. Winter leaves commenced their growth during December, after more than two months of winter activity of ''summer'' leaves. The latter were gradually shed during late spring, showing a longevity of almost one year. Winter leaves and any remaining old summer leaves were massively shed at late June, leaving on the shrubs the young summer leaves developed during last spring. During the late winter/early spring co-occurrence, the two kinds of leaves had comparable size, pigment content and maximum photosynthetic rates, but could be easily distinguished by the higher reflectance of summer leaves. The adaptive significance of the observed leaf developmental pattern is discussed in relation to the constraints of the Mediterranean climate.
(EN)
