Phosphorus Availability Is Related to the Growth of White Spruce in Some Reconstructed Sites in the Athabasca Oil Sands Region.

Reclamation practices need to address nutrient limitations in reconstructed soils in the oil sands region to ensure successful reestablishment of tree species. This study investigated P availability in reconstructed soils and its relationship to the growth performance of white spruce (Sw, Picea glauca). Study sites consisted of peat-mineral soil mix (PMM) as the capping soil over overburden (OB) substrate in the Athabasca oil sands region, Alberta, Canada. Soil samples were obtained from PMM and OB layers along a productivity gradient of Sw. It was hypothesized that P availability is different between the PMM and OB layers and that soil P is a limiting factor for Sw growth on low productivity sites. Available P (AvP) measured using the modified Kelowna method showed that AvP in PMM (0.5 – 1 mg kg^-1) was related  to the aboveground biomass increment (ABI) (p < 0.05) and accounted for 50% of the variation in ABI; however, there was no significant relationship between ABI and AvP in OB (0.5 ± 0.1 mg P kg^-1).  The P sorption was correlated with AvP in PMM (r = 0.67, p < 0.05) indicating that the high P sorption in high productive sites did not limit P availability. Sequential fractionation of P in PMM revealed that organic-P fraction is greater than the Ca-Mg-P fraction in high productive sites, while the opposite was observed in low productive sites. In all sites, Ca-Mg-P fraction was the greatest in OB. The large amount of Ca-Mg-P fraction reduced the P availability due to low solubility of Ca-P and Mg-P at the high pH (>7) prevailed in PMM and OB.  Phosphorus availability for Sw was mainly affected by the composition of PMM in reconstructed soils. Reclamation practices need to address P fertility in low productive sites for a better growth performance of Sw on reconstructed soil.