Phosphorus availability and fractionation vary among forest site types in reconstructed oil sands soils

We investigated relationships between phosphorus (P) availability and fractionation and growth of lodgepole pine (Pinus contorta var. latifolia Engelm. ex S. Watson) and white spruce (Picea glauca (Moench) Voss) in the Athabasca oil sands region. The study sites had peat – mineral soil mix (PMM) as cover soil over a tailings sand substrate planted to pine or an overburden substrate planted to spruce. Available P was determined using a modified Kelowna extraction and sequentially extracted to obtain exchangeable, Fe- and Al-bound, Ca- and Mg-bound, organic, and residual P. The organic P content in PMM explained 83% and 65% of the variations in available P in the pine and spruce sites, respectively. Phosphorus bound to Fe and Al in PMM was also positively related to available P on pine sites (p < 0.001) but not on spruce sites. Available P in PMM was correlated with aboveground biomass increment of spruce (p < 0.05) and explained 78% of the variation in foliar P. Foliar P in both pine and spruce was lower than the adequate level for tree growth. Low foliar P and available P in PMM affect the successful establishment of pine and spruce trees on the reclaimed sites, and proper P nutrition management is important to overcome P limitation in reclaimed soils.