Interspecific competition for nitrogen between early successional species and planted white spruce and jack pine seedlings

Abstract

Relatively little is known about belowground competition for nitrogen (N) between boreal forest species. The objective of this study was to compare the relative competitiveness of three early successional boreal forest species, trembling aspen (Populus tremuloides Michx.), fireweed (Epilobium angustifolium L.), and calamagrostis (Calamagrostis canadensis (Michx.) Beauv.), on 15N uptake and the growth response by containerized white spruce (Picea glauca (Moench) Voss) and jack pine (Pinus banksiana Lamb.) seedlings. Three densities (0, 2, and 6 plants/pot) of each competitor species were interplanted with individual seedlings in pots with 15N-labelled fertilizer and grown for 3 months. The conifer seedlings had the greatest fertilizer 15N uptake (129.5 and 82.3 µg/m2 root for white spruce and jack pine, respectively) when grown in monoculture and the lowest uptake when interplanted with six competitor plants (9.2 and 8.6 µg/m2 root for white spruce and jack pine, respectively). Whether grown in monoculture or with conifer seedlings, calamagrostis took up the greatest amount of fertilizer 15N. Vegetation management practices that reduce the establishment of this grass species in the field should benefit N uptake and growth of outplanted white spruce and jack pine seedlings.