Fall fertilization of Pinus resinosa seedlings: nutrient uptake, cold hardiness, and morphological development

•  Fall fertilization may increase plant nutrient reserves, yet associated impacts on seedling cold hardiness are relatively unexplored. •  Bareroot red pine (Pinus resinosa Ait.) seedlings in north-central Minnesota, USA were fall fertilized at the end of the first growing season with ammonium nitrate (NH$_{4}$NO$_{3})$ at 0, 11, 22, 44, or 89 kg N ha$^{-1}$. Seedling morphology and cold hardiness [assessed by freeze induced electrolyte leakage (FIEL)] were evaluated six weeks after fertilization and following the second growing season. •  Seedling height and number of needle primordia increased with fertilizer rate for both sampling years. Seedlings fertilized with 44 and 89 kg N ha$^{-1}$ attained target height (15 cm) after the second growing season. Shoot and root N concentration increased after the first growing season in fall fertilized seedlings compared to controls. Fall fertilized seedlings had lower FIEL (i.e., increased cold hardiness) compared to controls when tested at –40 °C after the first growing season, but no significant differences in FIEL of control and fertilized seedlings were observed after the second growing season. •  Results suggest that fall fertilization of red pine seedlings can help render desired target height in the nursery, while maintaining or increasing cold hardiness levels.Fertilisation automnale des plants de Pinus resinosa : absorption des éléments nutritifs, rusticité au froid, et développement morphologique. • La fertilisation automnale peut augmenter les réserves en éléments nutritifs des plants, mais les répercussions sur la rusticité au froid des semis sont encore relativement inexplorées. •  Des plants à racines nues de Pinus resinosa Ait.dans le centre-nord du Minnesota (USA) ont été fertilisés à l'automne à la fin de la première saison de croissance avec du nitrate d'ammonium (NH$_{4}$NO$_{3})$ à 0, 11, 22, 44, ou 89 kg N ha$^{-1}$. La morphologie des plants et la rusticité au froid [estimée par la fuite d'électrolyte (FIEL) induite par le gel] ont été évaluées six semaines après la fertilisation et à la suite dans la deuxième saison de croissance. •  La hauteur des plants et le nombre de primordiums d'aiguilles ont augmenté avec le taux de fertilisation pour les deux années d'échantillonnage. Les plants fertilisés avec 44 et 89 kg N ha$^{-1}$ ont atteint l'objectif de hauteur (15 cm) après la deuxième saison de croissance. La concentration en N des tiges et des racines a augmenté après la première saison de croissance chez les plants fertilisés à l'automne par rapport aux témoins. Les plants fertilisés à l'automne ont eu un plus faible FIEL (c'est-à-dire, une augmentation de rusticité), comparativement aux témoins lors du test à –40 °C après la première saison de croissance, mais aucune différence significative de FIEL entre plants fertilisés et témoins n'a été observée après la deuxième saison de croissance. • Les résultats suggèrent que la fertilisation d'automne des plants de Pinus resinosa Ait. peut aider à obtenir l'objectif de hauteur souhaité dans la pépinière, tout en maintenant ou en augmentant les niveaux de rusticité au froid

Regional Assessment of N saturation using foliar and root d15N

N saturation induced by atmospheric N deposition can have serious consequences for forest health in many regions. In order to evaluate whether foliar may be a robust, regional-scale measure of the onset of N saturation in forest ecosystems, we assembled a large dataset on atmospheric N deposition, foliar and root and N concentration, soil C:N, mineralization and nitrification. The dataset included sites in northeastern North America, Colorado, Alaska, southern Chile and Europe. Local drivers of N cycling (net nitrification and mineralization, and forest floor and soil C:N) were more closely coupled with foliar than the regional driver of N deposition. Foliar increased non-linearly with nitrification:mineralization ratio and decreased with forest floor C:N. Foliar was more strongly related to nitrification rates than was foliar N concentration, but concentration was more strongly correlated with N deposition. Root was more tightly coupled to forest floor properties than was foliar . We observed a pattern of decreasing foliar values across the following species: American beech>yellow birch>sugar maple. Other factors that affected foliar included species composition and climate. Relationships between foliar and soil variables were stronger when analyzed on a species by species basis than when many species were lumped. European sites showed distinct patterns of lower foliar , due to the importance of ammonium deposition in this region. Our results suggest that examining values of foliage may improve understanding of how forests respond to the cascading effects of N deposition