Nitrogen uptake characteristics for roots of conifer seedlings and common boreal forest competitor species

Abstract

Little is known about the N uptake abilities of competitor species and planted seedlings in the boreal forest. The objective of this study was to determine the Michaelis–Menten kinetic parameters of NH4+and NO3–for white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb.) seedlings, and three competitive common boreal forest early successional species: aspen (Populus tremuloides Michx.), fireweed (Epilobium angustifolium L.), and cala magrostis (Calamagrostis canadensis (Michx.) Beauv.). Uptake kinetics were measured in hydroponic cultures and expressed as maximum uptake (Imax) and ion affinity (Km). The ranking of Imaxvalues (pmol·cm-2·s–1) for NH4+uptake was calamagrostis (84.6), fireweed (58.1), white spruce (20.7), aspen (12.5), and jack pine (10.9), and for NO3–uptake was calamagrostis (17.7), fireweed (12.5), aspen (5.8), white spruce (4.5), and jack pine (2.1). The ranking of Kmvalues (µM) for NH4+uptake was calamagrostis (125.9), fireweed (163.8), aspen (205.7), white spruce (217.1), and jack pine (270.5), and for NO3–uptake was calamagrostis (229.9), fireweed (274.6), aspen (336.5), white spruce (344.5), and jack pine (350.5). Calamagrostis exhibited the greatest uptake rates and affinity for NH4+and NO3–, suggesting that silviculture practices that specifically reduce establishment of this grass should benefit the growth of planted seedlings.