Physiological and biochemical characterization of Acacia stenophylla and Acacia albida exposed to salinity under hydroponic conditions

Soil salinity is considered a serious environmental issue in many countries of the world, including Pakistan. A hydroponic experiment was carried out to study different mechanisms of salinity tolerance in two Acacia species, namely Acacia stenophylla A. Cunn. ex Benth. and Acacia albida Delile. Uniform seedlings of both species were grown for 28 days in half-strength Hoagland's nutrient solution with 0, 100, or 200 mmol . L-1 NaCl concentrations. The results revealed that shoot biomass decreased by 21% and 29% at the lower salinity level (100 mmol . L-1 NaCl) and by 44% and 55% at the higher salinity level (200 mmol . L-1 NaCl) in A. stenophylla and A. albida, respectively. The respective reductions in root biomass of both species were 20% and 29% at the lower salinity level and 36% and 54% at the higher salinity level. The physiological attributes such as chlorophyll and relative water contents decreased to a greater extent in A. albida than in A. stenophylla. As a result of oxidative stress, membrane stability index (MSI) decreased in both species, with a greater reduction in A. albida. Among different antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), the highest increase (sixfold) was observed in SOD activity in A. stenophylla. This study concludes that A. stenophylla is more salinity tolerant than A. albida as it maintained better ionic balance and higher activities of antioxidant enzymes and, as a result, higher biomass production.