Functional Traits and Their Plastic Response of Bassia dasyphylla under Salt-Alkaline Mixed Stress in a Desert Region, Northwestern China

The plastic response of Bassia dasyphylla (Fisch. & C.A. Mey.) Kuntze functional traits to saline-alkali land habitat and its mechanism were investigated. Two neutral salts, NaCl and Na2SO4, and two alkali salts, Na2CO3 and NaHCO3, were mixed in various ratios according to the varying ranges of salinity and pH in a natural soil, and the response of B. dasyphylla seedlings to salt-alkaline stress was determined. The osmolyte contents, peroxidative damage, antioxidant enzyme activity and plant morphology and biomass were determined. Thirty different salt-alkaline ecological treatments were applied, including ranges of salinity of 50–250 mmol/L and pH values of 7.10–10.19. The soluble sugar, soluble protein, proline, betaine, hydrogen peroxide and malondialdehyde contents, $${\text{O}}_{2}^{ - }$$ production rate and cell membrane permeability of B. dasyphylla rose with increases in salt concentration and pH. There were differences between the treatment groups and the control (P < 0.05). The activities of superoxide dismutase, peroxidase and ascorbate peroxidase enzymes initially increased and then decreased, but catalase activity continued to increase. The plant height, main root length, stem thickness, branch number, lateral root number and root, stem and leaf biomass were significantly decreased compared with the control (P < 0.05). In regard to biomass, the proportion of root biomass increased, but the proportions of stem and leaf biomass decreased. The correlations between the salt component ions and the above plant characteristics indicated complex effects of salt composition on the functional characteristics of B. dasyphylla. This study suggests that salt-alkaline environments inhibited the functional characteristics of B. dasyphylla and negatively affected several physiological responses and morphological plasticity.