Dissertation Research: Black Birch Seedlings as Foragers forNitrogen

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Forest regeneration is dependent on the successful growth of individual trees, which are directly affected by soil nitrogen availability. Soil nitrogen is heterogeneously distributed, both in terms of ammonium:nitrate ratio and total quantity. Previous work has shown that black birch seedlings perform differently when fed nitrate in comparison with ammonium, and that this response varies with rate of nitrogen supplied and light level. Using a split pot design to create patches of different ammonium to nitrate ration, the investigators will examine whether black birch seedlings forage selectively for nitrate or ammonium in soil. By using labelled 15NO3, they will test whether roots actually prefer to acquire ammonium, and whether preference for a given form of nitrogen is dependent upon the ratio of ammonium to nitrate in a patch, the rate of nitrogen supply and light availability. Lastly, the investigators will examine whether the ratio of total non-structural carbohydrates: free amino acids in the leaves is a good predictor of whole plant partitioning of biomass.