Effect of salinity on rhizosphere acidification and antioxidant activity of two acacia species

Salinity is a major environmental stress that is reducing crop yield, particularly in arid and semi-arid regions of the world. It is responsible for many physiological and biochemical disorders in plants. To investigate its effects on two acacia species, namely Acacia ampliceps Maslin and Acacia nilotica L., a solution-culture experiment was conducted in which both species were exposed to NaCl concentrations of 100 and 200 mmol.L-1. After four weeks of salinity stress, plants were harvested, and physical-growth data were recorded. The membrane stability index and activities of antioxidants enzymes such as superoxide dismutase, peroxidase, and catalase were determined using standard methods. Root exudates were collected for the analysis of organic acids, i.e., citric acid and tartaric acid. Root ash alkalinity was also measured. The results indicated that salinity stress caused a significant increase in the activities of antioxidant enzymes and in the release of organic acids in both species. Higher activities of antioxidant enzymes resulted in less damage to membranes and produced more shoot and root biomass in A. ampliceps than in A. nilotica. Likewise, having more rhizosphere acidification enabled A. ampliceps to respond in a better way to salinity stress than A. nilotica.