Textural interfaces affected the distribution of roots, water, and nutrients in some reconstructed forest soils in the Athabasca oil sands region

Re-constructed soils in the reclaimed landscape in the Athabasca oil sands region (AOSR) usually consist of an upper amendment layer (cover soil) and a substrate layer below. The cover soil used is typically peat-mineral mix (PMM) and the substrate can be materials such as tailings sand (TS) and fine-textured overburden (OB) materials. Abrupt changes in soil properties between the cover soil and the lower substrate layer create the so-called textural interface that can restrict water and nutrient movement and subsequently affect root growth. To assess the effect of the textural interface on the distribution of roots, water, and nutrients, we collected soil samples from the 10–5, 5–2, and 2–0 cm layers above and 0–2, 2–5, and 5–10 cm layers below the interface (zero at the interface) from nine sites each of PMM/TS and PMM/OB that were planted to lodgepole pine (Pinus contorta) and white spruce (Picea glauca) trees, respectively. Fine root (<2 mm) biomass (FRB) decreased logarithmically (p < 0.01) through the interface. The greatest decrease was found between 5–2 and 2–0 cm above the interface in TS due to lack of capillary rise of water and at the interface in OB due to compaction of fine-textured OB material. Based on stepwise regression analysis, volumetric water content and NH4-N or DON explained the variation of FRB in TS while electrical conductivity (EC) was the main parameter explaining FRB in OB. Our results indicate that management practices need to consider the influence of textural discontinuity or textural interface on the distribution of fine roots, water and nutrients and for water and N availability in TS and salt stress in OB as potential limiting factors for improving tree growth in the reclaimed/reconstructed landscape in the AOSR.