Root hypoxia aggravates the effects of saline tailings water on the growth and physiology of woody plants

Abstract Aims Oil sands mining in the boreal forest produces large volumes of liquid tailings. Research has generally focused on the thickness and composition of the soil layers to be placed on top of the tailings during reclamation. However, tailings release water, which may seep into the root zone and affect plants. Furthermore, the interactions and combined effects of root hypoxia and root substrate chemistry on plant responses are poorly understood. Methods The effects of the aqueous phase of novel tailings (Non-Segregating Tailings—NST) were studied under well-aerated and hypoxic conditions in three relatively hypoxia resistant tree species [tamarack (Larix laricina), black spruce (Picea mariana), and balsam poplar (Populus balsamifera)] and three relatively sensitive tree species [lodgepole pine (Pinus contorta), jack pine (Pinus banksiana), and aspen (Populus tremuloides)] by growing them in hydroponic solutions in a controlled environment. Results Root hypoxic conditions further reduced the survival, growth, and physiology of plants exposed to NST. Our results confirm that NST water produces the same deleterious effects in plants as previously reported in the amalgamated oil sands tailings. In trembling aspen, salt sequestration was inhibited, and in black spruce needles hypoxia may have prevented an osmoregulative mechanism. Conclusions Our results highlight the potential impact of water seepage from buried tailings on reclamation success. Furthermore, hypoxic conditions can aggravate these effects by inhibiting salt stress mechanisms. We suggest that the preparation of reclamation sites impacted by tailings water should involve efforts aimed at improvement of soil aeration to minimize the detrimental effects on plants.