Revue internationale d'écologie méditerranéenne International ...

A. DJABEUR, M. KAID-HARCHE, D. CÔME, F. CORBINEAU
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milieu à – 1MPa. L’élimination de la dormance
par une conservation au sec de 12 mois à la température
ambiante entraîne un élargissement de
la gamme de températures permettant une germination
rapide. Cependant, l’optimum thermique
reste similaire à celui des semences fraîchement
récoltées, c’est-à-dire 20-25 o C. La
dormance résulte principalement des enveloppes,
mais le caryopse nu joue aussi un rôle
dans la photosensibilité des semences entières.
L’intensité de la dormance dépend du lieu de
récolte ; elle est plus profonde pour les semences
récoltées dans la zone semi-aride (cytotype polyploïde,
2n = 40) que pour celles collectées sur les
hauts plateaux arides (cytotype diploïde, 2n
= 16). Le rôle écologique de la dormance et de
la post-maturation au sec est discuté en relation
avec l’établissement de cette espèce dans un
environnement aride.
Introduction
Lygeum spartum L. (Poaceae), commonly
named esparto, is an important perennial grass
in semi-arid and arid areas in Algeria (Aimé
1988; Le Houérou 1995). With Stipa tenacissima
L. and Aristida pungens Desf. this grass
makes a natural fence against desert expansion.
In addition to its ecological role, Lygeum
spartum has an economical interest in traditional
craftsmen and paper manufacturing
(Harche et al. 1991). For local purposes it is
then important to try to maintain the natural
populations of this plant and to increase their
regeneration potential. However, although
numerous works have been devoted to the
germinaton of seeds of various annual and
perennial desert plants (Baskin & Baskin
1998; Gutterman 2002), to our knowledge
only few studies (Conesa et al. 2007; 2009)
have been performed on the suitability of
Lygeum spartum for phytostabilisation of acid
mine tailings but no study has been carried
out in order to determine the main environmental
factors regulating the seed germination
in this plant.
Seed germination is subjected to a very precise
regulation, the complexity of which originates
both in the action of various external
factors and in the seeds themselves (Bewley
& Black 1982; Côme & Corbineau 1998).
Water, oxygen and temperature are the three
essential factors in germination, but light may
also play a role in many seeds (Bewley &
Black 1982; Côme & Corbineau 1998). However,
seeds are often unable to germinate, or
do so with great difficulty, even placed in conditions
that are apparently favourable for ger-
mination (good supply of water, good oxygenation,
apparently good temperature); they
are considered as dormant (Bewley & Black
1982; Côme & Corbineau 1998). Seed dormancies
do not correspond to a complete
inability to germinate, they are generally relative
phenomena the expression of which
depends on external factors (Bewley & Black
1982; Côme 1982; Côme & Corbineau,
1998). They should be viewed as systems for
regulating germination and ensuring the survival
of wild species by extending the timerange
over which germination occurs, or by
allowing germination only at certain times of
the year (Bewley & Black 1982; Baskin &
Baskin 1998; Gutterman 2002). Although
dormancy depends first on the seed genotype,
it is well known that it can be largely modulated
by the environmental factors in which
the mother plants are developing, such as
daylength (Evenari et al. 1966; Kigel et al.
1977; Gutterman 1985) and temperature
(Datta et al. 1972; Do Cao et al. 1978).
Dormancy of grass and cereal seeds is known
to be progressively lost during their storage in
the dry state under ambient conditions (Bewley
& Black 1982; Simpson 1990; Côme &
Corbineau 1998). This breaking of dormancy,
usually termed after-ripening, is expressed by
a widening of the temperature range within
which good germination occurs (Côme et al.
1984; Simpson 1990). When they are no more
dormant, these seeds are also less sensitive to
oxygen deprivation and light than before
breaking of their dormancy (Simpson 1990;
Corbineau & Côme 1996). In wild grasses
from semi-arid and arid areas, dormancy is
lost during the dry season, and then caryopses
become capable of germinating by the following
winter or spring rains (Gutterman et
al. 1996; Baskin & Baskin 1998).
The aims of the present work were (i) to
determine the main characteristics and the origin
of dormancy of two cytotypes of Lygeum
spartum seeds collected in two different geographic
regions in Algeria, a littoral semi-arid
zone (polyploid cytotype, 2n = 40) and an arid
zone (diploid cytotype, 2n = 16) (Benmansour
& Kaid-Harche 2001; Djabeur et al. 2008),
(ii) to investigate the effects of temperature,
white light and water potential of the medium
on the germination of freshly harvested seeds,
and (iii) to study whether dormancy is broken
in dry seeds, in order to improve our grasp of
the establishment of the species under natural
conditions.
ecologia mediterranea – Vol. 36 (1) – 2010