Exponential fertilization promotes seedling growth by increasing nitrogen retranslocation in trembling aspen planted for oil sands reclamation

Vegetation reestablishment in land reclamation is often challenged by high mortality and slow growth of planted species because of low nutrient availability and severe understory competition. We tested the effectiveness of exponential fertilization in nursery trembling aspen (Populus tremuloides Michx.) seedling production for improving revegetation success on reconstructed soils in the Oil Sands in a two-year field experiment using a 2 (exponentially vs conventionally fertilized seedlings) × 2 (weed intact vs weed removed) factorial design. The experiment was conducted on two different cover soil types: peat mineral soil mix (PMM) and LFH mineral soil mix (LFH). Nitrogen (N) retranslocation in outplanted seedlings was traced using 15N labeling. Exponential fertilization and weed removal increased height and root collar diameter growth but did not affect seedling survival over two growing seasons. Exponential fertilization increased new stem and leaf biomass and N content but decreased the percent allocation of biomass to roots. On average, 80% (on the PMM site) and 73% (on the LFH site) of total N demand of new tissues was met by internal N retranslocation. Exponential fertilization increased N retranslocation by 34% (P < 0.01) and 25% (P = 0.02) on the PMM and LFH sites, respectively. Weed competition reduced N retranslocation by 37% (P < 0.01) and N uptake by seedlings from the soil by 61% (P = 0.01) on the LFH site. We conclude that greater accumulation of nutrient reserves and greater N retranslocation helped to increase the growth of exponentially fertilized aspen seedlings that were outplanted for oil sands reclamation. Exponential fertilization of aspen seedlings for oil sands reclamation should be operationally tested for improving land reclamation in the Oil Sands.