Assessing N competition between outplanted conifer seedlings and early successional plants using ion-exchange membranes
During the early establishment phase, outplanted white spruce (Picea glauca (Moench) Voss.) and jack pine (Pinus banksiana Lamb.) seedlings are vulnerable to lethargic growth or mortality because of interspecific competition for soil nutrients, particularly nitrogen (N). Accurately quantifying the degree of N competition is essential for supporting effective vegetation management decisions. This study evaluated N competition at four boreal forest sites, three years following outplanting, using two-week in situ burials of ion-exchange membrane (IEM) in plots with and without vegetation management (VM). The effect of noncrop N uptake on soil N availability also was assessed using conventional 2N KCl extractions. Vegetation management continued to support increased conifer seedling growth, with no effect on survival compared to control plots. Although the N supply rate measured using IEM (Plant Root Simulator™-probes) were not correlated (P >0.05) with 2N KCl-extracted N concentration, there was a correlation (R2 = 0.68 to 0.76, P <0.01) between N supply rate and seedling growth. Ammonium-N supply rate was better correlated than NO3--N with conifer seedling growth, which is in agreement with preferential NH4+-N uptake by conifer species. The results of this study support the use of in situ IEM burials for monitoring soil N bioavailability during the early establishment phase.
boreal forest species
nitrogen supply rate
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