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