Περίληψη:
Leaves of 14 representative Mediterranean plant species were collected
on a monthly basis and assayed for UV-absorbing compounds concentration,
either on an area or a dry mass basis, from 1995 to 1997, Strong
seasonal fluctuations were observed in eight species tall evergreens,
two phrygana, one deciduous, one summer perennial and one winter
perennial). Two different patterns of changing concentrations of
UV-absorbing compounds were observed. In the first, concentration of
these compounds was higher in young developing leaves and concentration
declined during maturation, whereas in other plants, the opposite trend
was observed. These differences could be attributed to the particular
leaf surface morphology of each plant. The observed seasonal
fluctuations of UV-absorbing compounds seem to be more correlated to
developmental processes, than to seasonal fluctuations of the naturally
occurring UV-B radiation. Most of the winter perennials did not show
strong fluctuations during the period of development. The concentration
of these compounds varied not only on a seasonal basis among the
examined plants, but between different life forms as well: during
winter, examination of the leaves of 13 species showed that evergreen
sclerophylls and phrygana had at least two-fold higher concentration of
UV-B-absorbing compounds on a leaf area basis than winter perennials. In
addition, during the same season and irrespective of life form and
species, the absorbance at 300 nm per unit of mature leaf area followed
an asymptotic exponential decrease when specific leaf area increased.
The UV-B radiation screening capacity of the leaves of these plants is
discussed in relation to each adaptive strategy.
Συγγραφείς:
Liakoura, V
Manetas, Y
Karabourniotis, G
