Assessing N Competition Between Outplanted Conifer Seedlings and Early Successional Plants Using Ion-Exchange Membranes
Hangs, R., K. Greer and C. Sulewski. 2003. Soils and Crops
Abstract
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.
Key Words
boreal forest species, ion-exchange membrane, jack pine, nitrogen supply rate, PRS™probes, white spruce
