Precipitation is the most crucial factor in determining the seasonal emergence of seedlings of the three tested species in the field. The vertical distribution of seeds in sand determines the proportion of seeds that germinate after precipitation and acts to maintain seed banks over multiple years.

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The effects of sodium chloride (NaCl), polyethylene glycol-6000, temperature and light on germination and the effects of NaCl on growth were investigated in two Chinese desert shrubs, Haloxylon ammodendron (C.A.Mey.) Bunge and H. persicum Bunge ex Boiss. et Buhse. Both species occur in non-saline sand dunes; H. ammodendron also occurs in saline land, although it is not dominant there. Percentage germination of H. ammodendron and H. persicum in -3.0 MPa (667 mmol kg -1 ) NaCl was 91 and 64%, respectively. Hydroponic culture of each species for c. 3 months with NaCl solutions of 0, 200, 400 and 600 mmol kg -1 showed that the survival of H. ammodendron was highest (82.3%) at 400 mmol kg -1 NaCl, while that of H. persicum decreased with increasing NaCl concentration and was low (11.1%) at 400 mmol kg -1 NaCl. Sodium concentration in shoot tissues of 99-day-old seedlings grown at 400 mmol kg -1 NaCl exceeded 1000 mmol kg -1 in both species, while Na concentration in non-transpiring young seedlings grown in 400 mmol kg -1 NaCl was 240 and 350 mmol kg -1 for H. ammodendron and H. persicum, respectively. The results indicate that both species have relatively low adaptability to salinity at the older seedling stage compared with that at the germination and young seedling stage, and that H. ammodendron shows higher adaptability to salinity at the older seedling stage than H. persicum. It was concluded that salinity adaptability in the later developmental stage of these species determines their distribution with respect to salinity.

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Saline soils contain multiple types of salt, each of which may exert a different effect on seed germination and seedling growth of plants. The effects of five types of salt on the initial growth of Haloxylon ammodendron, a shrub found on both saline and non-saline areas in deserts of China, were investigated. Seeds were incubated at 20°;C in the dark in a solution (0 to –5.1 MPa) of a salt (NaCl, MgCl2, CaCl2, Na2SO4 or MgSO4) or polyethylene glycol (PEG)-6000, or in a salt (NaCl or MgCl2) or PEG solution containing a low concentration of CaCl2. Seed germination, seedling growth and cation (Na+, Mg2+, Ca2+ and K+) contents of seedlings were examined. Each salt had a different effect on seed germination, seedling growth and influx and outflux of cations in the seedlings. In both NaCl and MgCl2 treatments, the addition of low concentrations of CaCl2 favoured seed germination and seedling growth, and reduced K+ outflux from seedlings, but caused no appreciable decrease in the influx of Na+ or Mg2+ into seedlings. Marked abnormalities in seedlings were found only in treatments with Mg2+ salts, but these effects were completely alleviated by a low concentration of Ca2+ (Ca2+/Mg2+ = 0.012). The different responses of the initial growth in H. ammodendron to different isotonic salt solutions were attributed to differences among salt components in membrane permeability, toxicity and effects on functions of the plasma membrane and/or the cell wall.