Differential Effects of Six Salt Types on Wheat (Triticum aestivum L.) Germination and Seedling Growth

Soil salinization, characterized by complex ionic compositions, threatens global wheat production. Current research often focuses on single salts, leaving a gap in systematic comparisons of specific salt effects. This study comprehensively evaluated six prevalent salts (NaCl, Na2SO4, KCl, NaHCO3, MgSO4, and MgCl2) across concentrations (10–200 mmol/L) during wheat (Triticum aestivum L.) germination. By integrating ten physiological indicators with principal component analysis (PCA), membership function evaluation, and median lethal concentration (LC50) calculation, we identified distinct salt-specific toxicities. Results established a clear toxicity hierarchy: MgCl2 was consistently most toxic (LC50 = 32.92 mmol/L), indicating Mg2+/Cl− synergy, while KCl was least inhibitory (LC50 = 159.66 mmol/L). PCA simplified the 10-trait dataset, extracting 1 principal component (PC, 89.29–92.35% contribution) for most salts (fresh weight as key loading, reflecting growth) and 2 PCs (95.65% cumulative contribution) for MgSO4 (separating root-growth and germination-vigor responses), thus identifying salt-specific key evaluation traits. Building on this PCA-derived trait screening, this analysis further revealed fresh weight (FW), germination rate (GR), shoot length (SL), and simple vigor index (SVI) as core evaluation indicators, and identified distinct mechanistic pathways: while most salts caused a generalized growth inhibition reflected in biomass reduction, MgCl2 exerted a more specific and severe inhibitory effect on shoot elongation. MgSO4 uniquely employed dual pathways, separately affecting root and germination traits. An innovative aspect of this work is the synergistic application of three synergistic evaluation methodologies with multi-physiological parameters, which allows for the rigorous quantitative characterization of distinct salt-specific effects on both early germination and seedling growth in wheat. This laboratory-based study provides a theoretical framework and practical indicators for salt damage risk assessment and preliminary screening of salt-tolerant wheat germplasm and lays a foundation for field validation and targeted management strategies for specific saline–alkali soils.