Revue internationale d'écologie méditerranéenne International ...

162
◆ L. M. M. BIDAK
Value of correlations Seed mass
Germination %
Seed size
Petri-dish
-0.136
0.031
Half- water (HFC)
0.024
0.147
Full water (FFC)
-0.063
0.096
Number of Days of survival
Petri- dish for annuals
0.866** 0.470**
Petri- dish for perennials
0.520*
0.371*
Half-Water for annuals
Half-Water for perennials
and seed mass especially when water is available in the
habitats (e.g. canal bank, fallow fields, wadi & catchment
area). When availability of water decreased and habitats
tend to be drier, no significant correlation is obtained
(e.g. the inland plateau, saline depression, sand dunes and
rocky cliffs). These results are confirmed by the correlation
value between seed size and mass of plant species
collected from the catchments areas, desert and railway
roads, where occasional availability of water occurs
depending on the rain or other sources.
DISCUSSION
0.700**
0.194
** Correlation is significant at the 0.01 probability level.
* Correlation is significant at the 0.05 probability level.
Table 5. Values of Pearson’s two-tailed correlation.
0.587**
0.348
The size and shape of the studied seeds are extremely
variable. These characteristics depend on the form of
the ovary, the condition under which the parent plant is
grown and obviously on the species. Other factors, which
determine the size and the shape of seeds, are the size of
the embryo and the amount of the endosperm. Several
authors (e.g. Mott, 1972; Pate & McComb, 1981) have
argued that the germination events in arid and semi-arid
regions are triggered by large rainfall events and so the
developing seedlings may not face water stress for some
time. Many species showed adaptations to ensure germination
only under favorable soil moisture conditions and
may have characteristics such as mucilaginous gel or hairs
which improve the soil-seed contact to maximize water
uptake (Pate & McComb, 1981).
Habitats can be classified along a spectrum from
environments permitting fast growth rate to environments
permitting only slow growth rate, due to low soil
nutrients or moisture or to other impediments to plant
growth. Species occupying slow growth habitats tend to
have naturally slow relative growth rate even when given
favorable conditions (e.g. Grime, 1974, 1977; Chapin,
1980, 1991). In the present study, results of germination
and growth performance of the plant species collected
from the saline and inland plateau habitats revealed that
seedling growth, emergence, germination and establishment
of seeds were more affected than those collected
from other habitats. This may be attributed to the stressful
effect of the habitat and this seems to be in agreement
with the finding trend suggested by Grime (1974, 1977)
and Chapin (1980, 1991).
Resources in the embryo and endosperm of a seed
are deployed during germination to construct a seedling.
Different plant species provision their seeds with different
quantities of resources to support seedling establishment.
Species span a range of seed mass from less than 10 -6
to more than 10 4 g (Harper, 1977). Differences across
species in seed coat thickness, dispersal structures, water
contents and mineral nutrient concentrations reflect a
wide range in the dry mass of resources provided by
the mother plant to each of its offspring (Westoby et al.,
1992). Results obtained in the present study demonstrate
that large seeds could allow seedling to survive for longer
days after emergence. On the other hand, small size offer
short period of persistence from emergence, which is in
agreement with the results obtained by Westoby et al.
(1992). The present study also indicates that it is not likely
to relate the seed size to the seed mass. In other words,
large seeds are not always heavy and small seeds are not
necessarily light (e.g. Rununculus and Carduus).
Results of several comprehensive studies (e.g. Schimpf,
1977; Sorenson & Miles, 1978; Stronberg & Patten, 1990)
have suggested that plants in xeric habitats tend to have
larger seeds, and consequently larger seeds might provide
an advantage for seedling establishing in dry conditions.
However, this study showed that xeric habitats tend to
have smaller seeds. The advantage of large seeds in the
arid and semi-arid habitats may be due to the fact that
large seeds disperse over smaller distance and may attract
herbivores (Westoby & Leishman, 1994). A seed may be
large because it encloses an embryo (and endosperm)
which have genotypes that are able to attract a greater
than average supply of nutrient resources (Mogie et al.,
1990). However, the number of seeds and their size in
the present study seem to be largely determined by the
ecology of the species.
It is evident that very few species could tolerate more
than 2% of NaCl solution (Chapman, 1966). This con-
ecologia mediterranea, tome 29, fascicule 2, 2003