Nutrient enrichment of white spruce seedlings during nursery culture and initial plantation establishment

Growth and nutrient dynamics of bare-root white spruce (Picea glauca (Moench) Voss) seedlings were monitored for three years in a nursery and for one season after planting to assess effects of three nursery fertilization regimes. Nitrogen (totaling 0, 650, and 1300 kg N ha(-1) for 3 years) was applied conventionally in equal amounts during the growing season. The high-N treatment, representing a nutrient loading regime, was also applied seasonally at exponentially increasing rates as a fourth treatment. By the end of the 3-year nursery rotation, the N treatments had stimulated growth by 104-180% and nutrient uptake by as much as 381, 224 and 145% for N, P and K, respectively, inducing large accumulations of N and P in both conventionally and exponentially loaded seedlings. Compared with exponentially loaded seedlings, the concentrations of nutrients were less in conventionally loaded seedlings although their biomass was larger (31%). High nutrient reserves in the seedlings at the end of the nursery rotation resulted in increased biomass production (40-190%) after planting, which was related to the ability of the seedlings to retranslocate internal reserves for new growth, despite little or no net uptake of nutrients during the first season after planting. Compared with conventionally loaded seedlings, retranslocation was greater in exponentially loaded seedlings, which had accumulated larger and more readily available nutrient reserves during the nursery phase. The shortness of this study limits its usefulness for predicting the persistence of the loading response after planting, but we postulate that the high nutrient status of loaded seedlings at the end of the nursery rotation will contribute to future growth through increased nutrient storage and retranslocation, thus prolonging the loading response.