We report the short‐term effects of simulated nitrogen (N) deposition on the understorey of a boreal forest in northern Sweden. Doses of 15N double‐labelled NH4NO3 (0·5, 12·5, 25·0 and 50·0 kg N ha–1) were applied to 1 m2 plots in the summer of 1995 and plants were harvested the following autumn. 2. No significant treatment effects were found in either above‐ or below‐ground biomass which was distributed as follows: the ericaceous shrub Vaccinium myrtillus contributed 76%, the grass Deschampsia flexuosa 4%, and the bryophytes Dicranum majus and Pleurozium schreberi 20%. 3. The recovery of applied N in these species was 24, 27, 27 and 32% of the 0·5, 12·5, 25·0 and 50·0 kg N ha–1 applications, respectively, and thus the recovery increased with the N dose. 4. In the 0·5 kg N ha–1 treated plots, the highest concentrations of fertilizer‐derived 15N were found in the bryophytes, while in plots given the three higher N applications, leaves of D. flexuosa had the highest concentrations. 5. N application resulted in elevated concentrations of free amino acid N, which indicate increased storage of N in plant tissues. Furthermore, the N application resulted in increased damage to V. myrtillus by natural enemies. The severity of disease caused by two foliar parasitic fungi showed a clear numerical response to N treatment, as did the amount of herbivory as a result of Lepidoptera larvae.
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Nordin et al. (1998) studied this question.