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Abstract: In Alberta, Canada, oil sands mining activities have disturbed many boreal forest habitats and produced large amounts of tailings. Recently, a novel oil sands tailings management technology of the enhanced non-segregated tailings (eNST) has been developed, which uses polymers to accelerate tailings consolidation and reduce their salinity levels. However, the effects of eNST on the growth of plants that are used for reclamation of oil sands have not been thoroughly studied. Additionally, some tailings reclamation areas may be prone to waterlogging since water released by the tailings may infiltrate the root zone and affect plants. In my thesis research, I carried out two studies to examine the effects of eNST on plants. The first study examined the effects of eNST release water on the seedling growth and physiological responses of four tree species commonly used for the oil sands reclamation: paper birch (Betula papyrifera), trembling aspen (Populus tremuloides), jack pine (Pinus banksiana), and black spruce (Picea mariana) under well-aerated and hypoxic conditions in hydroponics. The study showed that eNST water impaired the growth and physiological processes of all plants and that root hypoxia can aggravate the negative effects of eNST. After two months of treatments, paper birch and jack pine had significantly higher leaf Na concentrations compared with trembling aspen and black spruce. Moreover, jack pine and black spruce had higher leaf Na/K ratios compared with paper birch and trembling aspen. The eNST water significantly reduced chlorophyll concentrations, net photosynthesis, and transpiration rates in paper birch and trembling aspen, but not in jack pine and black spruce. Root hypoxia aggravated the negative effects of eNST water on paper birch, resulting in higher leaf Na/K, Na/Ca ratios, lower net photosynthesis, and impaired growth. Root hypoxia had a stronger inhibitory effect on the net photosynthesis rates in jack pine and black spruce compared with the eNST water. In summary, the first experimental results demonstrated that eNST water significantly reduced the growth and physiological parameters in paper birch and trembling aspen. The root hypoxia aggravated the negative effects of eNST water on the growth parameters and chlorophyll concentrations of paper birch, jack pine, and black spruce. The second study examined the role of salinity in the phytotoxicity of eNST water. In this study, a halophytic grass (Puccinellia nuttalliana), a relatively salt-tolerant grass (Poa juncifolia), and a relatively salt-sensitive grass (Poa pratensis) were subjected in hydroponics to treatments with eNST supplemented with 0, 60, and 120 mM NaCl The results demonstrated that the growth and physiological processes in Puccinellia nuttalliana were unaffected by the 100% eNST water regardless of NaCl concentrations. The 50% eNST water did not affect the growth and physiological processes of Poa juncifolia. In 100% concentration of eNST water and in the treatments with supplemented NaCl, the growth of Poa juncifolia was significantly reduced. The growth of Poa pratensis was inhibited in all treatment groups. The study pointed to salinity as the major factor contributing to the phytotoxicity of eNST water. In summary, Puccinellia nuttalliana is more tolerant to eNST water than Poa juncifolia and Poa pratensis. The high eNST water tolerance of Puccinellia nuttalliana can be likely partly attributed to its salt exclusion ability. Poa pratensis was the most sensitive of the three studied grass species to all applied treatments. The addition of NaCl to 50% eNST water aggravated the negative effects of the eNST water on Poa pratensis.