Growth, Nitrogen Uptake and Retranslocation in Exponentially Fertilized Trembling Aspen Seedlings Planted for Oil Sands Reclamation.

Vegetation re-establishment in oil sands reclamation is often challenged by high mortality and slow growth of planted trees because of growth limiting factors such as low nutrient availabilities and high understory vegetation competition. Application of nursery exponential fertilization in trembling aspen (Populus tremuloides Michx.) to enhance revegetation success in reconstructed soils was tested in a field experiment for two years in a 2 (exponentially vs conventionally fertilized seedlings) × 2 (weeds intact vs weeds removed) factorial experiment in reclamation sites with two different organic cover soils: peat mineral soil mix (PMM) and LFH mineral soil mix (LFH). N retranslocation in seedlings was traced using 15N isotope. Overall, survival was not affected by the treatments but height and root collar diameter were increased by exponential fertilization and weed removal over two growing seasons. Exponentially fertilized seedlings yielded more new stem and leaf biomass than conventional ones but percentage allocation of biomass to roots was greater in conventional seedlings. N content of seedlings was also increased by exponential fertilization. About 73 to 80% of total N demand of new tissues was met by internal N retranslocation. N in new tissues derived from old tissues was increased by exponential fertilization while N uptake from the soil was not changed by the treatment. Weed competition reduced N retranslocation in both PMM and LFH sites but N uptake from the soil was reduced only in the LFH site by weed competition. The increased growth and N retranslocation in exponentially fertilized seedlings can be attributed to greater nutrient reserve built up in these seedlings. The potential use of exponentially fertilized aspen seedlings in oil sands reclamation should be tested operationally and applied in future land reclamation efforts.