Root dynamics and plasticity of boreal species on reclaimed saline-sodic overburdens and naturally saline sites.

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There are about 6500 ha of reclaimed landscapes in the oil sands region, the majority of which consists of materials with high levels of salts in the overburden capped on top with a peat/mineral soil cover up to 1.5m thick. Cover thickness has ecological implications in that thicker covers will minimize negative effects of upward salt migration from the overburden on root systems but also reduce water yield for downstream wetlands. In addition, thicker covers cost more which has economic ramifications for companies. How thick should these covers be? To answer that we need to know how root systems for boreal species such as aspen and spruce are impacted by salinity and cover thickness. Do roots systems demonstrate enough plasticity to develop under these saline conditions to support a healthy forest and how do root distributions on these reclaimed covers mimic root distributions found on naturally saline or non-saline sites? Recent research has shown that root samples collected from these reclaimed landscapes are found in the saline overburdens. However, we do not know if these roots belong to the desired boreal tree species planted there or from understory vegetation because of inadequacies of morphological root identification techniques. Therefore the objectives are to 1) determine the rooting distribution by species (aspen, spruce, selected understory) using DNA sequencing techniques in natural stands, naturally saline sites, and reclaimed saline-sodic landscapes of varying thickness; 2) quantify root dynamics and function in reclaimed landscapes compared to natural stands using minirhizotron (underground camera) and tracer techniques; and 3) determine the plasticity of aspen and spruce roots to salinity conditions using 3D root architecture models. For Obj. 1 roots will be collected from natural stands, naturally saline sites, and reclaimed saline-sodic landscapes of varying thickness and identified with DNA sequencing techniques to conclusively know where in the soil profiles the root systems are distributed. Root dynamics in Obj. 2 will be measured in reclaimed and natural sites using minirhizotrons where clear plastic tubes are inserted into the ground and root images collected on a monthly basis with a miniature video camera. Root function (N uptake) will be measured using stable tracers placed at various depths and measured in the aboveground portion of the vegetation. To investigate root plasticity of these root systems in Obj. 3, a 3D root architecture model will be used with input parameters obtained from excavated root systems to model the effect of varying cover thicknesses and migrating salt profiles on root plasticity and root development. This proposal will provide oil sand companies and regulators with results that will help in certifying reclaimed landscapes and minimize risks of cover failure by ensuring that root systems are developing properly compared to natural forests.