Root identification, 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 that is capped on top with a peat/mineral soil cover up to 1.5 m thick. The thickness of these covers has ecological implications in that thicker covers will minimize negative effects of salt migration from the overburden into the cover on root systems but also reduce water yield for downstream wetlands. In addition, thicker covers are more expensive to design and thus have economic ramifications for companies. How thick should these covers actually be? To answer that we need to know how root systems for boreal species such as aspen and spruce are impacted by cover thickness - do roots of these planted trees actually occupy the entire soil profile, or are they restricted to just the soil surface due to the upward migrating salt profiles? Do roots of boreal species demonstrate enough plasticity to develop under these salinity conditions in order 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 high salt overburdens. However, we do not know if these roots belong to the desired boreal tree species planted there or from understory vegetation or weeds because of inadequacies of morphological root identification techniques. Therefore the objectives of this proposal are to 1) determine the rooting distribution by species (aspen, spruce, selected understory) using DNA sequencing techniques and their morphological traits in natural stands, naturally saline sites, and reclaimed saline-sodic landscapes of varying thickness; 2) quantify root dynamics and activity in reclaimed landscapes compared to natural stands using minirhizotron (clear tubes in the ground that use cameras to capture root images) and tracer techniques coupled with DNA sequencing; and 3) determine the plasticity of aspen and spruce roots to saline-sodic 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 characteristics will also be measured to determine the plasticity of the roots between the overburden and cover layers compared with natural and naturally saline sites. 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. The activity of the roots 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 project is novel in that it uses DNA sequencing techniques to actually identify individual roots to understand how cover thickness is affecting root development and thus tree growth as well as providing a tool for predicting the effects of salts and cover thickness on root development. This program will provide results that are significant to oil sand companies and regulators in certifying reclaimed landscapes and minimize risks of cover failure by ensuring that root systems are developing properly compared to natural forests.