A. Soltani - Dept. of Forest Sciences, ShahreKord University, ShahreKord, Iran. E-mail: ali.soltani@nres.sku.ac.ir

Daily counts of germinated seeds of white saxaul (Haloxylon persicum) incubated at ۳۵ different hydrothermal environments (۱۰-۲۵?C and ۰ to -۳ MPa) were carried out under controlled laboratory conditions. The seeds were then buried in sand at ۴ different depths in well drained pots constantly moisturized for three weeks. In all these hydrothermal conditions, the courses of germination were completed in less than ۱۲ days. Both temperature and water deficit conditions significantly affected the seed germination. Water potential values of -۱.۵ MPa reduced the germination percentage to less than one fourth of the potential viability in all ambient temperature regimes and seed germination almost completely ceased at water deficit of -۳ MPa. As water potential decreased from ۰ to -۱.۵, base temperature values slightly increased from ۵.۴ to ۶.۵ ?C. Six-cm depth of burial was enough to reduce germination by ۵۰% and on an average ۸۵% of germinated seeds at ۸-cm depth failed to reach the soil surface. No seedling appeared on top of the sand bed in pots labeled \"۱۲-cm burial depth".   REFERENCES Akhani, H., Ghorbanli, M. (۱۹۹۳) A contribution to the halophytic vegetation and flora of Iran. In: H. Lieth and A. Al-Masoom (Eds.), Towards the rational use of high salinity tolerant plants, Kluwer Academic Publishers, Amsterdam, pp. ۳۵-۴۴. Akhani, H., Trimborn, P., Ziegler, H. (۱۹۹۷) Photosynthetic pathways in Chenopodiaceae from Africa, Asia and Europe with their ecological, phytogeographical and taxonomical importance. Plant Syst. Evol., ۲۰۶, ۱۸۷- ۲۲۱. Alvarado, V., Bradford, K.J. (۲۰۰۲) A hydrothermal time model explains the cardinal temperatures for seed germination. Plant Cell. Environ., ۲۵, ۱۰۶۱-۱۰۶۹. Amani, M., Parvizi, A. (۱۹۹۶) [Silviculture of saxaul]. Forests and Range Lands Research Center Publication, Tehran, ۱۱۸ p. Baskin, C.C., Baskin, J.M. (۲۰۰۱) Seeds: Ecology, Biogeography, and Evolution of Dormancy and Germination. Academic Press, San Diego, ۶۶۵ p. Bradford, K.J. (۱۹۹۰) A water relations analysis of seed germination rates. Plant Physiol., ۹۴, ۸۴۰–۸۴۹. Bradford, K.J. (۱۹۹۵) Water relations in seed germination. In: J. Kigel and G. Galili (Eds), Seed Development and Germination, Marcel Dekker, New York - USA, pp. ۳۵۱–۳۹۶. Dahal, P., Bradford, K.J. (۱۹۹۰) Effects of priming and endosperm integrity on seed germination rates of tomato genotypes. II. Germination at reduced water potential. J. Exp. Bot., ۴۱, ۱۴۴۱- ۱۴۵۳. Finch-Savage, W.E. (۱۹۹۵) Influence of seed quality on crop establishment, growth, and yield. In: A.S. Basra (Ed), Seed quality: basic mechanisms and agricultural implications, Food Products Press, New York, pp. ۳۶۱–۳۸۴. Finney, D.J. (۱۹۷۱) Probit analysis. Cambridge University Press London, ۳۳۲ p. Fyfield, T.P., Gregory, P.J. (۱۹۸۹) Effects of temperature and water potential on germination, radicle elongation and emergence of mungbean. J. Exp. Bot., ۴۰, ۶۶۷–۶۷۴. Gummerson, R.J. (۱۹۸۶) The effect of constant temperatures and osmotic potential on the germination of sugar beet. J. Exp. Bot., ۳۷, ۷۲۹-۷۴۱. Gutterman, Y. (۱۹۹۳) Seed germination in desert plants. Springer-Verlag, Berlin ; New York, ۲۵۳ p. Holt, J.S., Orcutt, D.R. (۱۹۹۶) Temperature thresholds for bud sprouting in perennial weeds and seed germination in cotton. Weed Sci., ۴۴, ۵۲۳-۵۳۳. Jafari, M., Niknahad, H., Erfanzadeh, R. (۲۰۰۳) Effect of Haloxylon plantation on some soil characteristics and vegetation cover. Desert, ۸, ۱۵۲-۱۶۲. Kardavani, P. (۱۹۹۴) Arid areas. Tehran University Publications, Tehran, ۳۱۸ p. Kebreab, E., Murdoch, A. (۲۰۰۰) The effect of water stress on the temperature range for germination of Orobanche aegyptiaca seeds. Seed Sci. Res., ۱۰, ۱۲۷–۱۳۳. Kebreab, E., Murdoch, A.J. (۱۹۹۹) Modeling the effects of water stress and temperature on germination rate of Orobanche aegyptiaca seeds. J. Exp. Bot., ۵۰, ۶۵۵-۶۶۴. Koocheki, A. (۱۹۹۶) The use of halophytes for forage production and combating desertification in Iran. In: R. ChoukrAllah, C.V. Malcolm and A. Hamdy (Eds), Halophytes and biosaline agriculture, Marcel Dekker, Inc., New York, pp. ۲۶۳-۲۷۴. Matin, M., Chegini, M.A., Borbar, Z., Modares, M. (۱۹۹۴) Seed pelleting as a method to improve success in aerial seeding of Haloxylon species. Seed and Seedling breeding Institute, Isfahan, ۱۱۳ p. Maun, M.A. (۱۹۹۸) Adaptations of plants to burial in coastal sand dunes. Can. J. Bot., ۷۶, ۷۱۳-۷۳۸. Maun, M.A. (۲۰۰۴) Seeds and seed banks. In: M.L. Martínez and N.P. Psuty (Eds.), Coastal dunes: ecology and conservation, Springer-Verlag, Berlin. Michel, B.E. (۱۹۸۳) Evaluation of water potential of solutions of polyethylene glycol ۸۰۰۰ both in the absence and presence of other solutes. Plant Physiol., ۷۲, ۶۶-۷۰. Minitab Inc. (۲۰۰۰) MINITAB Reference Manual, Release ۱۳ for Window™. Minitab Inc., State College. Nemati, N. (۱۹۸۶) Pasture improvement and management in arid zones of Iran. J. Arid Environ., ۱۱, ۲۷-۳۵. Pyankov, V.I., Black, C.C., Artyusheva, E.G., Voznesenskaya, E.V., Ku, M.S.B., Edwards, G.E. (۱۹۹۹) Features of photosynthesis in Haloxylon species of Chenopodiaceae that are dominant plants in Central Asian deserts. Plant Cell Physiol., ۴۰, ۱۲۵-۱۳۴. Rowse, H.R., Finch-Savage, W.E. (۲۰۰۳) Hydrothermal threshold models can describe the germination response of carrot (Daucus carota) and onion (Allium cepa) seed populations across both sub- and supra-optimal temperatures. New Phytol., ۱۵۸, ۱۰۱-۱۰۸. Song, J., Feng, G., Tian, C., Zhang, F. (۲۰۰۵) Strategies for adaptation of Suaeda physophora, Haloxylon ammodendron and Haloxylon persicum to a saline environment during seed-germination stage. Ann. Bot., ۹۶, ۳۹۹-۴۰۵. Steinmaus, S.J., Prather, T.S., Holt, J.S. (۲۰۰۰) Estimation of base temperatures for nine weed species. J. Exp. Bot., ۵۱, ۲۷۵-۲۸۶. Tobe, K., Li, X., Omasa, K. (۲۰۰۰) Effects of NaCl on seed germination and growth of two Chinese desert shrubs, Haloxylon ammodendron and H. persicum (Chenopodiaceae). Aust. J. Bot., ۴۸, ۴۵۵-۴۶۰. Unknown (۲۰۰۶) [National annual report of synoptic and climatologic meteorology stations]. I.R. Iran Meteorology Organization, Tehran, ۲۳۶ p. Wang, R., Bai, Y., Tanino, K. (۲۰۰۵) Germination of winterfat (Eurotia lanata (Pursh) Moq.) seeds at reduced water potentials: testing assumptions of hydrothermal time model. J. Exp. Bot., ۵۳, ۴۹–۶۳. Wang, Z.L., Wang, G., Liu, X.M. (۱۹۹۷) Experiment on germination ecology of some desert plants. J. Desert Res., ۱۷, ۴۴-۴۹. Zheng, Y., Xie, Z., Yu, Y., Jiang, L., Shimizu, H., Rimmington, G.M. (۲۰۰۵) Effects of burial in sand and water supply regime on seedling emergence of six species. Ann. Bot., ۹۵, ۱۲۳۷-۱۲۴۵. Zohary, M. (۱۹۷۴) Geobotanical foundations of the Middle East. J. Ecol., ۶۲, ۳۴۹-۳۵۰.

Seed germination, hydrothermal time analysis, seed burial, Haloxylon persicum