Abstract: In Gurbantonggut Desert, the population degeneration of Haloxylon ammodendron mainly occurs on the plain and small dunes (<5 m in height), while on the nearby large dunes (> 10 m in height), the plants can grow normally. In this paper, a comparative study was made on the age structure of H. ammodendron population, its seeds and seed germination characteristics under different salinity gradients, soil physical and chemical properties, and their effects on the population regeneration of H. ammodendron between degenerated and normal areas in small scale (under the conditions that the climatic factors and plant population age were similar). In degenerated area, H. ammodendron seedlings were lack, and the natural regeneration of H. ammodendron was hampered. There were significant differences in the hundred-seed weight with and without fruiting wings and the fruiting wing’s diameter of H. ammodendron among the three habitats (plain, small dunes, and large dunes). The seed germination rate of H.ammodendron had no significant difference under non salt-stress condition, but had significant difference under salt-stress condition and decreased with increasing salt concentration, suggesting that the limitation of the regeneration had no relationship with seed characteristics but close relationship with soil salinity. The soil physical and chemical properties in the three habitats were significantly different, and the soil electrical conductivity on the plain and small dunes was much greater than that on large dunes. The plant density of living H. ammodendron population was significantly negatively correlated with the electrical conductivity and water content of different soil layers, and the number of H. ammodendron seedlings (<40 cm in height) was significantly negatively correlated with the electrical conductivity of 0-30 cm soil layer. To sum up, high soil salinity severely decreased the plant density of H. ammodendronpopulation, restrained the seed germination and the seedling’s survival rate, and eventually led to the unhealthy natural regeneration of H. ammodendron.

Key words: Green algae, Tetraselmis, Axenic culture