White and Black Spruce Seedling Development Using the Concept of Relative Addition Rate

Ingestad's concept of relative addition rate was used to grow a range of seedling types, of both black (Picea mariana) (Mill.) B. S. P.), and white spruce (Picea glauca (Moench) Voss). Seedlings were grown for about 18 weeks in styrofoam containers under greenhouse conditions, and fertilized at exponentially increasing rates of either one, two, four or six per cent per day, following a one month pretreatment period. Pretreatment consisted of applying a nutrient solution proportionally low in nitrogen, but that had a relatively high conductivity compared to the initial solutions used in the exponentially increasing fertilizer treatments. Black spruce seedlings grew fastest, had significantly more root development or had a higher efficiency of nitrogen uptake when nutrients were applied at exponentially increasing amounts. In contrast, white spruce grew more rapidly when fertilized with a constant level of fertilizer (control treatment). Biomass allocation and nitrogen concentrations in seedlings of both species varied significantly with treatment, indicating that various levels of nitrogen stress had been achieved. It is suggested that different seedling stock types, which are acclimated to various levels of nutrient stress, can be produced by controlling the rate of nutrient addition.