Early outplanting performance of nutrient-loaded containerized black spruce seedlings inoculated with Laccaria bicolor: a bioassay study

Early growth potential of nutrient-loaded and (or) Laccaria bicolor (R. Mre.) Orton inoculated (Picea mariana (Mill.) BSP) seedlings was investigated using pot bioassays retrieved from a low-competition feathermoss site and a high competition hardwoodAlnus site in the boreal forest. Mycorrhizal seedlings were similar in biomass and shoot/root ratio to nonmycorrhizal seedlings at planting but significantly higher in nutrient content depending on fertilization regime and loading rate. After transplanting, both nutrient-loaded and inoculated seedlings outperformed conventional seedlings, increasing dry matter production by 20-49% with loading and by 45-92% with combined treatments. Nutrient uptake followed similar trends, increasing N, P, and K uptake by 80-124, 89-129, and 72-106%, respectively, for combined treatments compared with conventional seedlings, demonstrating the advantage of both nutrient loading and inoculation in early plantation establishment. Seedling response was greater on the feathermoss site, presumably because of less competition for nutrients and light. Vector diagnosis indicated the response was associated with a primary limitation of N and P that was alleviated by nutrient loading and mycorrhizal inoculation, particularly when treatments were combined. A strong correlation between preplant N content and outplant biomass suggests that initial nutritional status is a better criterion for predicting stock quality than traditional morphological parameters of seedlings.