Seed germination response of Haloxylon persicum (Chenopodiaceae) to different hydrothermal conditions and sand burial depths

Daily counts of germinated seeds of white saxaul (Haloxylon persicum) incubated at 35 different hydrothermal environments (10-25?C and 0 to -3 MPa) were carried out under controlled laboratory conditions. The seeds were then buried in sand at 4 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 12 days. Both temperature and water deficit conditions significantly affected the seed germination. Water potential values of -1.5 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 -3 MPa. As water potential decreased from 0 to -1.5, base temperature values slightly increased from 5.4 to 6.5? C. Six-cm depth of burial was enough to reduce germination by 50% and on an average 85% of germinated seeds at 8-cm depth failed to reach the soil surface. No seedling appeared on top of the sand bed in pots labeled \"12-cm burial depth\".