Exponential fertilization and plant competition effects on the growth and N nutrition of trembling aspen and white spruce seedlings

Exponential fertilization has been shown to be a useful technique for improving seedling quality during nursery production. In this study, we evaluated (i) the impact of exponential vs. conventional fertilization on trembling aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) seedlings during nursery production and (ii) the growth performance and nitrogen (N) utilization of those seedlings in response to foxtail barley (Hordeum jubatum L.) competition after the transplantation of seedlings in a greenhouse experiment. Exponential fertilization with an application rate higher than the conventional fertilization increased the internal N reserve in trembling aspen and white spruce seedlings during nursery production and also increased new leaf, new stem, and old stem biomass and N retranslocation rates in trembling aspen seedlings but not in white spruce seedlings after transplantation. Foxtail barley competition decreased N concentrations in seedlings and soil N uptake by the seedlings; however, increased N retranslocation rates with foxtail barley competition were observed in white spruce seedlings but not in trembling aspen seedlings. Our results suggest that the growth performance of seedlings was improved by N loading, whereas the impact of vegetation management was species specific. Key words: exponential fertilization, internal N reserve, N-loaded seedling, net N retranslocation rate, vegetation competition. La fertilisation exponentielle s'est averee utile pour ameliorer la qualite des semis lors de la production en pepiniere. Dans cette etude, nous avons evalue (i) l'impact de la fertilisation exponentielle vs conventionnelle sur les semis de peuplier faux-tremble (Populus tremuloides Michx.) et d'epicea blanc (Picea glauca (Moench) Voss) lors de la production en pepiniere, et (ii) la croissance de ces semis et leur utilisation de N en reaction a la competition de l'orge queue-d'ecureuil (Hordeum jubatum L.) apres les avoir transplantes en serre suivant un dispositif experimental. La fertilisation exponentielle, dont le taux d'application est plus eleve que la fertilisation conventionnelle, a augmente les reserves internes de N chez les semis de peuplier faux- tremble et d'epicea blanc durant la production en pepiniere et a augmente la biomasse des nouvelles feuilles, des nouvelles et des vieilles tiges ainsi que le taux de retranslocation de N apres la transplantation chez les semis de peuplier faux-tremble mais pas chez les semis d'epicea blanc. La competition de l'orge queue-d'ecureuil a reduit les concentrations de N dans les semis et l'absorption de N dans le sol par les semis; cependant, en presence de l'orge queue-d'ecureuil une augmentation du taux de retranslocation de N a ete observee chez les semis d'epicea blanc mais pas chez les semis de peuplier faux-tremble. Nos resultats indiquent que la croissance des semis a ete amelioree par une surcharge de N tandis que l'impact de la maitrise de la vegetation dependait de chaque espece. [Traduit par la Redaction] Mots-cles : fertilisation exponentielle, reserves internes de N, semis surcharges en N, taux net de retranslocation, competition de la vegetation.
Introduction Vegetation management is one of the most critical silvicultural practices for maximizing postplanting tree seedling survival and growth during the early establishment phase of plantations (Lowery et al. 1993; [...]