Nitrate reductase activity has been measured in Sphagnum fuscum (Schimp.) Klinggr. growing on an ombrotrophic mire in subarctic Sweden, remote from urban and industrial sources of atmospheric pollution.
Perturbation experiments in the field demonstrated nitrate induction of nitrate reductase activity which was both rapid and concentration dependent. Cumulative nitrate reductase activity after repeated treatments with 1 mM nitrate declined with each successive treatment. It is suggested that this may be a result of intracellular ammonium accumulation. Nitrate reductase activity in plants subjected solely to wet and dry deposition from the atmosphere showed little diurnal change, and watering of Sphagnum fuscum hummocks with distilled water had no effect on the enzyme activity. Nitrate reductase activity was, however, shown to be induced by natural precipitation events, the cumulative induced activity being proportional to nitrate deposition.
The data suggest that the wet deposition of nitrate represents an important source of nitrogen for ombrotrophic Sphagnum species, and that there is a close coupling of the physiology of S. fuscum plants with their atmospheric environment. Such a relationship would be readily perturbed by atmospheric pollution.