Open-pit mining of oil sands in north-eastern Alberta produces large volume of saline tailings. Aside from tailings being saline, they have high levels of boron (B), naphthenates and low levels of oxygen. These stresses can further exacerbate toxic effects of salt on plants and, consequently, affect the successful revegetation of the oil sands mining areas. The general objective of the present study was to understand the mechanisms of salinity interactions with other stress factors namely, B, root hypoxia and naphthenic acids (NAs).

To address the objective, jack pine (Pinus banksiana ) seedlings were grown under controlled environment conditions and subjected to a combination of stresses, with salinity as a common stress factor. Results of the present work demonstrated the sensitivity of jack pine to salts and its susceptibility to salts was further increased by the presence of high concentrations of B, NAs and low levels of oxygen. Salinity altered jack pine responses to B. When present together with salts, B decreased survival and induced injury to plants. Among the distinct responses of jack pine to combined stresses were reduced root hydraulic conductance and stomatal conductance, which could alter root to shoot salt transport. The reduction in root water uptake observed in plants treated with NAs + NaCl explain the reduced accumulation of Na + and Cl- in the shoots. In another experiment, I observed that under hypoxic conditions, roots lost the ability to restrict Cl- uptake and the increase in Cl - concentrations was correlated with root electrolyte leakage suggesting that Cl- was partly responsible for membrane leakiness in the roots. Similar response was also observed in plants exposed to B + NaCl treatments, which showed that the Cl- -induced membrane injury was partly responsible for Na+ and B toxicity.

The implication of this research for the revegetation of the oil sands following mining operations is discussed.