Studies On Salt-resistance Of Seeds And Seedlings In Several Halophytes In Inland Arid Region

In the present study, the effect of salinity on the germination for euhalophyte and xerophyte, and the strategies for adaptation of halophytes to extreme saline and arid environments in Xinjiang during seed germination stage were investigated; the osmotic adjustment traits of euhalophyte and xerophyte were also investigated in field and controlled conditions. The main results were as followed:1. The effect of NaCl on seed germination was due to both osmotic stress and ion toxicity for both halophytes, e.g., Suaeda physophora and Haloxylon ammodendron, and xerophyte, e.g., Haloxylon persicum. The leakage of K+, the peroxidation of lipids and the disruption of membranes induced by NaCl were different between halophytes and xerophyte. However, it showed the same reponse in seed germination and recovery germination when seeds were pretreated in 700 mmol.L-1 NaCl both in halophyte and xerophyte.2. Low salt content in the soil was essential for halophytes during their seed germination and seedling establishment stages.3. The strategies for adaptation of halophytes to saline and arid environments during seed germination stage: (1) high salinity and temperature induce seeds to remain dormancy. Compared with Haloxylon persicum, more viable ungerminated seeds of H. ammodendron and S. physophora submerged in 700 mmol.L-1 NaCl can germinate rapidly when environmental conditions are favorable. High salinity and temperature induce seeds of euhalophytes Halostachys caspica, Kalidium foliatum and Halocnemum strobilaceum to remain ungerminated, and seeds germination and seedling establishment of the three halophytic species can be ensured only when temperature and edaphic conditions are favorable. This is most likely an important adaptive strategy in these halophytic species to survive their saline environment in an arid region in Xinjiang; (2) morphological adaptations. Seeds of S. physophora and H. ammodendron accumulated less Na+ in embryos but more Na+ were compartmentalized in the seed coats, which might protect embryos from ion toxicity to ensure seed viability during seed development. Cotyledons in seeds of S. physophora and H. ammodendron contain chlorophyll. Therefore, cotyledons in seeds can take the function of photosynthesis soon after seed germination to ensure seedling establishment when the environmental conditions are favorable; (3) the adaptations to low oxygen and dryness/moist interchange. Compared with S. physophora and H. ammodendron, seed germination, recovery germination and total germination were very low in H. persicum when seeds were submerged in 700 mmol.L-1 NaCl solution, especially for recovery germination and total germination when ungerminated seeds were air-dried and then transferred to distilled water, while these were increased markedly when seeds were submerged and aerated in 700 mmol.L-1 NaCl in H. persicum compared with that only submerged in 700 mmol-L-1 NaCl solution, and it may relate to their environmental factors.4. NO3--N plays both nutritional and importmant osmotic role in halophytes. In field condition, NO3- did not play important role in osmoregulation for both S. physophora and H. persicum in saline or sandy desert. In a greenhouse experiment, more NO3- were involved in osmoregulation or organic Nbiosynthesis in the leaves of S. physophora under high salinity (300 mmol.L-1 NaCl) compared with thatin stems of H. persicum; S. physophora is more responsive to NO3-N compared with H. persicum. different reponse to salinity and NO3--N may affect the natural distributing of S. physophora and H. persicum in certain saline or arid region.