• Populus alba ‘Villafranca’ tolerates moderate salinity (60 mM NaCl) without growth or biomass reduction. • High salinity (180 mM NaCl) induces basal leaf chlorosis, abscission, and fresh weight reduction. • Sodium accumulation increases with salinity and is mainly retained in roots and basal tissues. • Potassium decreases in roots but increases in leaves, contributing to K⁺/Na⁺ balance maintenance. • Calcium accumulation in leaves increases with stress intensity, supporting signaling and membrane stability. • High salinity activates phenylpropanoid and flavonoid pathways but reduces flavonol and proline levels. • Vacuolar NHX genes remain stable at 60 mM NaCl but are largely downregulated at 180 mM NaCl. Soil salinization has become a major ecological issue that limits plant growth and development by disrupting nutrient uptake and imposing ionic stress. This study examined the prolonged responses of morphological, physiological, and biochemical characteristics, as well as the expression of six vacuolar Na⁺/H⁺ antiporter (NHX) genes of the Populus alba L. “Villafranca” clone under 0, 60, 120, and 180 mM NaCl. P. alba L. “Villafranca” was able to tolerate a salt treatment of 60 mM NaCl without changes in height, biomass, although stomatal conductance and net photosynthesis were slightly reduced beginning in week two. At 180 mM, chlorosis and abscission in basal leaves were evident, and organ fresh weight decreased. Total chlorophyll remained stable until later in the treatment. Na⁺ accumulation increased under 180 mM NaCl in tissues except apical stems, consistent with partial exclusion/compartmentation. K⁺ concentration decreased in roots, whereas it increased in leaves, maintaining the K⁺/Na⁺ balance. The level of Ca 2+ increased in leaves as the stress concentration increased, supporting signaling and membrane selectivity. Phenylpropanoid pathway was induced under high stress, and proline increased under 60 mM NaCl but decreased at 180 mM. The expression of NHX genes remained stable under 60 mM NaCl in roots, basal, and apical leaves, but most were downregulated at 180 mM. Overall, these results highlight the complex, species-specific responses of poplar to salt stress and indicate that P. alba “Villafranca” is moderately salt-tolerant, maintaining physiological and ionic stability up to 60 mM NaCl.
Assabbane et al. (Sun,) studied this question.