Abstract:

The aim of this work was to evaluate the salt tolerance of four salt-tolerant plant species under different NaCl concentrations， with the goal of identifying germplasm resources for the “matching species to the land” strategy for saline-alkali soil improvement. The four halophytes were Atriplex aucheri， Suaeda salsa，Salicornia europaea， and Sesbania cannabina. These plant species were subjected to five NaCl treatments： CK （control）， T₁ （100 mmol·L^-1）， T₂ （200 mmol·L^-1）， T₃ （300 mmol·L^-1）， and T₄ （400 mmol·L^-1）. Their root morphology and physiological characteristics were analyzed， and their salt tolerance was evaluated. The main results were as follows： 1） In terms of the root response， NaCl had significant negative effects on the root length， root surface area， and root volume of S. salsa， A. aucheri， and S. cannabina （P<0.05）， but increased root diameter and root activity. This result indicates that these plants maintain salt tolerance by boosting root metabolic activity and thickening water-conducting tissues to reduce hydraulic limitations. 2） In terms of oxidative stress， NaCl stress led to increased contents of membrane lipid peroxidation products， namely malondialdehyde （MDA）， and increased hydrogen peroxide （H₂O₂） contents. S. cannabina exhibited the most pronounced H₂O₂ and MDA responses， with the H₂O₂ content in root increased by 68% in T₂ vs. CK and the shoot MDA content increased by 61% in T₁ vs. CK. In A. aucheri， the shoot and root peroxidase （POD） activities were increased by 36% and 8%， respectively， in T₁ compared with CK. Root catalase （CAT） activity in S. salsa peaked at T₂ （a 12% increase compared with CK）， suggesting that the three protective enzymes ［superoxide dismutase （SOD）， POD， and CAT］ act synergistically to scavenge reactive oxygen species and mitigate membrane damage. 3） In terms of ion homeostasis， S. salsa and S. europaea demonstrated superior Na⁺ and Ca²⁺ uptake. In the T₂ treatment， the Na⁺ content in the shoot of S. salsa was increased by 8.3%， and the Ca²⁺ content was increased by 98%. In S. cannabina， the shoot Na⁺ content was significantly lower than the root Na⁺ content compared to CK， implying that it resists salt stress through selective ion uptake. 4） The salt tolerance of the four species was evaluated by principal component analysis and a membership function analysis. The principal component analysis revealed that SOD activity， Na⁺ and K⁺ contents， POD activity， and root vitality are core indicators for salt tolerance assessment. The results of the membership function analysis showed that the four species could be ranked from most to least salt tolerant as follows： S. europaea>S. salsa>A. aucheri=S. cannabina.

Key words: salt stress, root structure, antioxidant enzymes, ion content