Integrative multivariate analysis reveals four distinct salinity tolerance strategies in Alstroemeria cultivars.

Salinity severely constrains the growth and ornamental quality of floricultural crops by disrupting plant morphology, photosynthetic performance, and redox homeostasis. This study investigated cultivar-specific morphophysiological and antioxidant responses of four Alstroemeria hybrida cultivars differing in growth habit (two dwarf: Inca Sweety and Dwarf Red; two tall: Orange Queen and Amatista) under increasing salinity levels (0, 20, 40, and 60 mM NaCl). Salinity induced distinct, cultivar-dependent response patterns across all measured traits. Dwarf cultivars exhibited superior structural stability, maintaining stem elongation, leaf area, and total chlorophyll content under moderate to severe salinity, whereas tall cultivars experienced pronounced reductions in biomass accumulation and pigment integrity. Inca Sweety displayed exceptional physiological homeostasis, characterized by stable chlorophyll indices, phenolic content, antioxidant capacity, and PAL activity, indicating effective prevention of oxidative damage rather than reactive detoxification. In contrast, Amatista showed high growth potential under non-stress conditions but exhibited sharp declines in growth, photosynthetic pigments, and antioxidant performance as salinity intensified. Antioxidant enzyme activities revealed mechanistic differences among cultivars: coordinated peaks of CAT and APX at moderate salinity in Amatista were followed by enzymatic collapse at high stress, while Inca Sweety exhibited delayed CAT induction but sustained activation of APX and GPX, suggesting a finely regulated H₂O₂-scavenging network. Overall, salinity tolerance in Alstroemeria was governed by the coordination, timing, and balance of antioxidant defenses rather than the magnitude of individual enzymatic responses. These findings highlight the importance of integrated redox regulation in determining cultivar performance under saline conditions and provide a mechanistic basis for selecting salt-resilient ornamental cultivars.