International Journal of Mediterranean Ecology - Ecologia ...

ADEL DHIEF, MUSTAPHA GORAI, SAMIRA ASCHI-SMITI, MOHAMED NEFFATI
26
events during the germination of Lepidium
sativum L. and Arabidopsis thaliana (L.)
Heyhn. Abscisic acid (ABA) specifically
inhibits the endosperm rupture of these two
closely related Brassicaceae species. In PD
seeds, the embryo-covering layers can confer
mechanical constraint (coat dormancy) that
must be overcome by the growth potential of
the embryo (Bewley 1997; Koornneef et al.
2002; Leubner-Metzger 2003; Kucera et al.
2005). C. arich has larger seeds than C. comosum
and C. azel. Experimentally, large seeds
have an advantage over small seeds by having
greater nutrient reserves for the young
seedlings to enable them to grow larger and
to tap resources earlier (e.g., water, sunlight,
mineral nutrients). Thus, seedlings from
large-seeded species could establish under a
range of environmental conditions that could
not be tolerated by seedlings from smallseeded
species, notably competition for
resources, and the capricious drought prone
environments (Westoby et al. 2002; Moles &
Westoby 2004). Seed age has been demonstrated
to be related to seed mass in that
smaller seeds can remain viable (in seed
banks) over longer periods than larger seeds
(Leishman et al. 2000). C. comosum has a
greater seed dry mass than C. arich and C.
azel. The difference in the rate of imbibition
among Calligonum species is largely a function
of seed dry mass and the density of seed
seta (Zhang 1992). Variations between seed
mass have been predicted to be of the greatest
significance to the initial seedling establishment
in arid zones (Susko & Lovett Doust
2000). Information on seed germination is
also important for the propagation of potentially
and economically important desert plant
species.
Conclusion
In conclusion, scarification treatments are one
of the most effective methods for germinating
Calligonum seeds. These experiments were
conducted in order to find practical methods
of seed treatment, which would improve the
germination of the three dominant and economically
important species widely distributed
in the active sand dunes in Southern
Tunisia. Chemical scarification for a minimum
of 20 min significantly improved the
germination of these species, suggesting that
dormancy in these seeds might be due to the
hardness and impermeability of the seed coat.
In the context of the potential use of Calligonum
species as an alternative in the arid
desert regions, it is our contention that seed
germination and seedling emergence under
the natural environmental conditions still
deserve further research.
References
Aronson J., Floret C., Le Floc’h E., Ovalle C. & Pontanier
R., 1993. Restoration and rehabilitation of
degraded ecosystems in arid and semi-arid lands. II.
Case studies in southern Tunisia, central Chile and
northern Cameroon. Restor. Ecol. 1: 168-186.
Auclair L. & Zaafouri M.S., 1996. La sédentarisation
des nomades dans le sud tunisien : comportements
énergétiques et désertification. Sécheresse 7 : 17-24.
Baskin C.C. & Baskin J.M., 1998. Seeds. Ecology, biogeography,
and evolution of dormancy and germination.
Academic Press, San Diego.
Baskin J.M. & Baskin C.C., 2004. A classification for
seed dormancy. Seed Sci. Res. 14: 1-16.
Bewley J.D., 1997. Seed germination and dormancy.
Plant Cell. 9: 1055-1066.
Bond W.J., Honig M. & Maze K.E., 1999. Seed size and
seedling emergence: an allometric relationship and
some ecological implications. Oecologia 120: 132-
136.
Chen R. & Fu J., 1984. Physiological studies on the seed
dormancy and germination of Erythrophloeum
fordii. Scientia Silvae Sinicae.
Cohn M.A., 1996. Operational and philosophical decisions
in seed dormancy research. Seed Sci. Res. 6:
147-153.
Derbel S., Chaieb M., 2007. Germination behaviour and
seedling establishment of two desert shrubs, Calligonum
polygonoides (Polygonaceae) and Spartidium
saharae (Fabaceae), under experimental conditions.
Acta Bot. Gallica 154 (4): 533-544.
Dhief A., Gorai M., Aschi-Smiti S. & Neffati M., 2009.
Comparative phenological and water potential patterns
of three Calligonum species in the eastern
Great Erg of Tunisia. Flora 204: 581-592.
Fan C. & Li X.W., 2004. The Dormancy of Forest Seed
and it’s Termination. (Forestry and Horticulture College,
Sichuan Agricultural University, Ya’an,
625014, Sichuan), Sichuan Forestry Exploration and
Design.
Fenner M. & Thompson K., 2005. The ecology of seeds.
Cambridge, UK: Cambridge University Press.
Finch-Savage W.E. & Leubner-Metzger G., 2006. Seed
dormancy and the control of germination. New phytol.
171: 501-23.
Gardarin A., Durr C., Mannino M., R. Busset H. & Colbach
N., 2010. Seed mortality in the soil is related
to seed coat thickness. Seed Sci. Res. 20: 243-256.
Hilhorst H.W.M., 1997. Seed dormancy. Seed Sci. Res.
7: 221-223.
Institut national météorologique (INM), 1996. Fiche climatique
des stations principales de la Tunisie. Rapports
et publications, Tunis, Tunisie.
ecologia mediterranea – Vol. 38 (1) – 2012