Ammonium and nitrate uptake characteristics of hydroponically-grown boreal forest tree species and selected understory vegetation

Non-Peer ReviewedWith increasing public concern regarding sustainable forest management, forest land managers are obligated to ensure successful seedlings establishment and growth, particularly within the first few years. In order to achieve this goal there needs to be adequate seedling uptake of moisture and nutrients from the soil. Under conditions of adequate soil moisture, a reduction in early growth of planted white spruce and jack pine seedlings (two important commercial tree species in Saskatchewan) through interspecific competition with non-crop vegetation is primarily attributed to reductions in seedling uptake of soil nutrients, particularly N. Despite numerous reports on the competitive inhibition of young conifer seedlings by native understory vegetation, no attempts have been made to compare the relative N uptake ability of conifer planting stock with native boreal forest competitors. A depletion experiment was conducted to study the relationship between N concentration and subsequent ion absorption by roots of five competing boreal forest species. By monitoring the decrease in solution N concentration over time, the relative NH4+-N and NO3--N uptake capacity of each species was quantitatively determined. Results from this study indicate that white spruce and jack pine seedlings have a lower measured NH4+-N and NO3--N uptake capacity compared to native forest competitors, making these conifers relatively poor competitors for available N in soil. Calamagrostis exhibited a superior capacity for NH4+-N and NO3--N uptake, suggesting that silvicultural practices that reduce the establishment of this grass species in the field will benefit the growth of planted conifer seedlings. A greater understanding of the relative N uptake capacity between conifer seedlings and native understory competitors may, therefore, lead to improved silviculture practices and subsequent plantation productivity