Physiological, biochemical and phytoremedial characterization of acacia species for salt affected soils

Abstract

Salinity is a major environmental stress which is reducing crop yields particularly in arid to semi-arid zones. In Pakistan large cultivated land is affected by various degrees of soil salinity and sodicity. There exists a great diversity among plant species for their salt tolerance. Selection of plant species capable of growing on salt-affected soils using saline waters is based on the capability of a crop to survive at higher levels of salinity and to provide useful end product. Keeping these facts in view, four studies were planned to explore the salinity tolerance and phytoremedial potential of two different acacia species viz Acacia ampliceps and Acacia nilotica. In the first experiment, three week old seedlings of both species were transplanted in half strength Hoagland nutrient solution having five treatments (control, 100, 200, 300 and 400 mM NaCl). The data regarding growth and ionic composition (Na+, K+ and Cl-) showed that A. ampliceps was more tolerant to salinity than A. nilotica. The seedlings of A. nilotica could not survive at 400 mM NaCl due to ion toxicity. In another solution culture experiment, the release of organic acids (citric acid, malic acid and tartaric acid) and comparative oxidative stress tolerance of these two species was investigated. More rhizosphere acidification and higher activities of antioxidants including, SOD, POD and CAT enabled A. ampliceps to produce more shoot and root biomass. Both the species were further studied under the combination of salinity and water stress in the pots where A. ampliceps proved to be better tolerant to salinity whereas A. nilotica performed better under water stress. In the final study these species were grown in the salt affected field and their growth and ionic data were recorded after every six months for two years. The changes in the soil chemical and physical properties were also determined at these intervals. The comparison of both species indicated that A. ampliceps produced more biomass and caused more reduction in the soil chemical properties like pHs, ECe and SAR as compared to A. nilotica, due to more addition of organic matter and rhizosphere acidification .On the other hand the physical properties like bulk density and infiltration rate were also improved more under A. ampliceps than under A. nilotica. So it would prove to be a good source of wood and forge for livestock at the same time rehabilitating barren lands.