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The effect of interspecific competition on conifer seedling growth and nitrogen availability measured using ion-exchange membranes

Hangs, R.D., K.J. Greer and C.A. Sulewski . 2004. Canadian Journal of Forest Research 34:754-761

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 the use of two-week in situ burials of ion-exchange membrane (IEM; Plant Root Simulator™-probes) for quantifying differences in soil N supply rate between different vegetation management treatments and the relationship of this N availability index to early growth of conifer seedlings at four boreal forest sites. At most sites, the effect of noncrop N uptake on soil N availability was apparent, with smaller NH4 -N, NO3--N, and total dissolved inorganic N (DIN) supply rates in control plots compared with vegetation management plots. Total DIN supply rate was correlated (R2 = 0.60 to 0.73, P < 0.01) with seedling height, root collar diameter, and stem volume growth. Ammonium-N supply rate was better correlated than NO3--N supply rate 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 burials of IEM for measuring soil N availability during the early establishment phase.

Key Words

boreal forest species, ion-exchange membrane, jack pine, nitrogen supply rate, PRS™-probes, white spruce