An experimental investigation of the effects of nitrogen deposition to Narthecium ossifragum

Narthecium ossifragum (L.) Hudson was subjected to artificial deposition events in three experiments. In the first, a laboratory experiment, 1·0 m nitrate significantly decreased the growth of Narthecium, and the shoot and root nitrogen content of the plants was increased in all enhanced nitrogen treatments. In the second experiment, solutes were applied in situ to a relatively unpolluted upland ombrotrophic mire at concentrations measured in cloud water at a polluted site in England. There was no effect on Narthecium tissue nitrogen concentration due to either ammonium or nitrate applied alone but the shoot nitrogen was significantly increased when the ammonium and nitrate were applied in combination. In the third experiment, a piece of upland ombrotrophic mire from a relatively unpolluted site in North Wales was transplanted to a polluted site in northern England. After two years both the shoots and roots of Narthecium present in the mire showed a higher nitrogen concentration in the transplant compared with the control. These data show that nitrogen supply in the southern Pennines is supra-optimal for Narthecium, which implies that in such situations it (and other species with a similar ecological strategy) would be out-competed by more vigorous species. The data from the field experiment at the relatively unpolluted site imply that even there, nitrogen supply is close to supra-optimal for Narthecium.