Salt stress tolerance strategies vary between different functional groups of plants of native semi-arid species

The increase in salinity in dry regions has contributed to the desertification of areas, increasing the need to identify tolerant species. The investigation of functional groups of plants clarifies adaptation strategies; however, in a saline environment, it has not yet been explored. The objective was to investigate how different functional groups of Caatinga plants respond to increased saline stress. Plants of deciduous species with high wood density (HWD) (Myracrodruon urundeuva and Bauhinia cheilantha), and deciduous species with low wood density (LWD) (Amburana cearenses and Pseudobombax marginatum) were evaluated. The saline concentrations (NaCl) were 0.15; 2.5; 3.5 and 4.5 dS m^-1 applied for 90 days. A completely randomized design was adopted in a 2 × 2 × 4 factorial scheme with five replications. At the end of the experiment, growth, stomatal conductance (gs), water potential (Ψ_xylem), chlorophyll fluorescence, salt content and enzymatic activity were analyzed. The data were subjected to polynomial regression analysis and Tukey test (5 %). The HWD group was classified as salinity tolerant and presented high values of gs (300 mmol m^-2s^-1), variation in Ψ_xylem (70 %), efficiency of photosystem II, number of leaves, and accumulation of salts in the leaves (K⁺ = 70 %, Na⁺ = 18 %, and Cl^- = 52.5 %). On the other hand, the LWD group was classified as moderately sensitive to salinity and showed a large reduction in growth and biomass with increased salinity, accumulation of ions in stem (Cl^- = 136 %) and root (Na⁺ = 44 %; Cl^- = 45 %), and higher enzymatic activity (45 %). Tolerance strategies to saline stress differ between different functional groups of Caatinga seedlings. The HWD group is more tolerant to salinity and represents a good alternative for the recovery of salinized areas.