Abstract
Previous studies have led to contrasting results about the role of overwintering leaves
as storage sites, which is related to leaf longevity and life-form. The aim of this
study was to evaluate the functional role of the leaves of four species of Mediterranean
sub-shrubs, with different leaf phenology, as sources of nitrogen (N) and non-structural
carbohydrates (NSC) for shoot growth. The seasonal dynamics of the concentrations
and pools of N and NSC were assessed monthly in the leaves and woody organs of each
species. Overwintering and spring leaves served as N and NSC sources for shoot growth
in the evergreen species analyzed, providing up to 73 % and 324 % of the N demand
for spring and autumn growth, respectively. Excess autumn N was stored in woody structures
which contributed to the N and NSC requirements of spring growth. In the winter deciduous
species, woody organs were the main N source for spring growth, while current photosynthesis
from immature brachyblasts seemed to be the main carbon (C) source. Due to their short
lifespan, overwintering and spring leaves did not show several translocation processes
throughout their life time, their contribution to new growth being made during senescence.
The successive exchange of leaf cohorts displayed by Mediterranean sub-shrubs might
serve as a mechanism to recycle N and C between consecutive cohorts as plants perform
the pheno-morphological changes needed to adapt their morphology to the seasonality
of their environment.
Key words
Resource storage - leaf senescence - chamaephytes - seasonal growth - leaf phenology
- seasonal dimorphism - cushion plant - winter deciduous.
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S. Palacio
Pyrenean Institute of Ecology (CSIC)
Av. Montañana 1005, Apdo. 202
50192 Zaragoza
Spain
Email: sarap@ipe.csic.es
Editor: H. Rennenberg