Growth and nitrogen retranslocation of nutrient loaded Picea mariana seedlings planted on boreal mixedwood sites

Enhanced nutrient mobilization from old to current growth is a key mechanism that confers competitive ability to nutrient-loaded black spruce (Picea mariana (Mill.) BSP) seedlings planted on high-competition forest sites in northern Ontario. This study examines effects of nutrient loading and differing vegetation management (herbicide, fertilization, shading) on growth, partitioning, and net retranslocation of N between current and old shoots of newly planted black spruce seedlings on six contrasting boreal sites. Nutrient loading during nursery culture improved seedling growth and N uptake and retranslocation after transplanting. Herbicide application accelerated growth and N uptake only on the high-competition Alnus, hardwood, and mixedwood sites but had no effect on the less competitive feathermoss and Vaccinium sites. Weed removal on competitive sites reduced N retranslocation significantly. Field fertilization reduced N retranslocation in seedlings and promoting tree growth and N uptake on the less competitive feathermoss and Vaccinium sites. However, fertilization stimulated weeds on high-competition sites suppressing seedling biomass and N uptake. Factors that seem to affect net N retranslocation include the type and level of internal N reserves, biomass and N accumulation and partitioning, external N supply, and other stresses that limit plant growth such as competition.