Nitrate Reductase Activity of Sphagnum Species in the South Pennines

SUMMARY Bulk deposition of nitrate, ammonium and organic nitrogen was greater at a South Pennine blanket peat site than at a similar, relatively unpolluted site in the Berwyn Mountains, North Wales. Sphagnum cuspidatum , transplanted from North Wales to the South Pennines, showed a rapid induction of nitrate reductase activity, which declined after 4 days. A laboratory induction experiment demonstrated a similar phenomenon on solutions containing 1 mM nitrate. In the presence of 1 mM ammonium, much less nitrate reductase activity was induced. Ammonium accumulated in both nitrate grown plants in the laboratory and in field transplants, which suggests that it may be responsible for the observed declines in enzyme activity. The results are discussed in relation to the nitrogen nutrition of blanket bog plants.