Growth, nutrient dynamics, and interspecific competition of nutrient-loaded black spruce seedlings on a boreal mixedwood site

Nutrient-loaded and conventionally fertilized containerized black spruce (Picea mariana (Mill.) BSP) seedlings were planted on a boreal mixedwood site in the Greater Clay Belt of Ontario to study their growth and interaction with natural vegetation. At planting, nutrient-loaded seedlings were similar in height and biomass to conventionally fertilized seedlings, but contained 39, 69, and 22% more tissue N, P, and K content, respectively. After two field growing seasons, nutrient-loaded seedlings attained 15-18% more height and 16-39% more biomass, resulting in 15-27% reduction in the biomass of neighbouring vegetation. Aboveground biomasses of seedlings and neighbouring vegetation were inversely related. Interspecific competition was more intense in the second year than in the first year of outplanting. Nutrient loading prior to planting stimulated nutrient uptake and root growth after planting, and reduced soil N availability by 6-20% during the first season, suggesting greater preemption of belowground nutrient resources. The enhanced competitive ability of loaded seedlings over naturally occurring vegetation was probably due to the contrasting nutrient utilization traits induced by greenhouse fertilization. Nutrient-loaded seedlings translocated more nutrients to actively growing parts from reserves built up during the greenhouse preconditioning phase than did conventionally fertilized seedlings. First-season growth and nutrient responses in the field and in previous greenhouse trials were significantly correlated, demonstrating the effectiveness of using intact bioassays to simulate and predict short-term field responses to competition treatments.