Effects of nitrogen addition on the growth of Vaccinium uliginosum and Vaccinium vitis-idaea

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Abstract
Nitrogen fertilization may affect plant growth by changing (i) shoot size and hence shoot weight,.(ii) shoot mortality, and (iii) shoot branching dynamics. This study assessed the effects of nitrogen addition on all three aspects of aboveground growth in cooccurring evergreen (Vaccinium vitis-idaea) and deciduous (Vaccinium uliginosum) species. Growth responses were used to estimate parameters for a model of overall shoot population growth. Shoot population size increased at similar rates in both species with nitrogen fertilization. However, the addition of nitrogen elicited a different type of response in each species. Vaccinium uliginosum showed an increase in the size of the shoots produced. This result, combined with the fact that larger shoots produced a greater number of daughter shoots, was responsible for the shoot population increase. In contrast, the addition of nitrogen increased the rate of lateral meristem release for shoots of all sizes in V. vitis-idaea. The ecological implications of the results are discussed with respect to evergreen and deciduous habits.
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