Objective  This study examined the effects of polyaspartic acid (PASP) dosages on the growth and physiological characteristics of desert plants under drought stress condition, and further to ascertain the suitable PASP dosage for plant growth, aiming to promote the application of drought-relief and moisture-conserving technology for ecological restoration in extreme arid area.

  Method  Two-year-old P. euphratica seedlings were selected as the research object, a field drought experiment was conducted to study the growth, photosynthetic characteristics and drought-resistance physiology of P. euphratica seedlings under different PASP application regimes, and a comprehensive evaluation on their impact efficiency was drawn out.

  Result  (1) Under drought stress condition, root application PASP could enhance the rhizosphere soil moisture and improve the water status of seedlings, and increase the plant height, ground diameter, increment of new shoot, number of photosynthetic organs and lateral roots, and growth rate, to significantly facilitate the growth of branches and leaves. (2) Root application PASP effectively widened light ecological amplitude, and increased stomatal conductance, intercellular CO₂ concentration, light energy and water use efficiency, and reduced respiratory consumption, to significantly improve photosynthetic capacity and resource use efficiency of seedlings. (3) Root application PASP effectively promoted the aboveground and underground biomass accumulation, and changed the biomass allocation ratio, and decreased the root shoot ratio, to significantly increase the seedling biomass. (4) Root application PASP significantly increased the concentrations of soluble protein, soluble sugar, and increased the enzyme activity of superoxide dismutase, peroxidase, and decreased the content of malondialdehyde. It strengthened the osmotic regulation and antioxidant capacity of seedlings. (5) A principal component analysis and multivariate data evaluation indicated that the water-retention and growth promotion effect of different PASP dosages were in the order of 10 g/plant > 15 g/plant > 20 g/plant > 5 g/plant > CK.

  Conclusion  In the practice of water-saving and drought-resistant afforestation in arid areas, the most suitable PASP dosage of P. euphratica seedlings is 10 g/plant, which provides scientific basis and reference for vegetation restoration in extremely arid desert areas.