Physio-biochemical characterization of two acacia species (A. karroo Hayn and A. saligna Labill.) under saline conditions

Abstract

Drought and salinity act simultaneously in tolerance and acclimatization under saline conditions. Therefore, plants subjected to these types of stress should have developed specific structural adaptations at the early stages of development. The solution to these environmental problems is to look for species that are relatively water-efficient and resistant to recurrent episodes of various abiotic stresses such as salt stress. In this study, the salinity tolerance index, ionic homeostasis and osmoprotection were evaluated in A. karroo and A. saligna plants of 90 days old and cultured at various concentrations of NaCl for 21 days. Results showed that salt caused remarkable changes in some growth-related parameters (dry biomass) represented by the salinity tolerance index (STI). Na⁺, Ca²⁺, and Ratio_Na+/K+ content in the leaves increased with salinity levels, while K⁺ contents were significantly reduced compared to the control in both acacia species. Levels of proline, total free amino acids and reducing sugars have been accumulated considerably in the leaves. A. karroo was more salt-tolerant than A. saligna. Our results showed that the adaptability of a species to salinity is closely related to ion selectivity and biomass production. The seedlings also accumulated significantly a set of important osmolytes in leaves under salt stress, showing a marked increase in secondary metabolite accumulation. This adaptation proved very specific to each species for better survival in saline environments.