Impact of nitrogen and phosphorus on C-14-lignocellulose decomposition by stream wood microflora

Labelled lignocellulose was incubated with homogenized surface wood scrapings (from a Douglas fir log in a Pacific Northwest stream) in distilled water, in stream water from 4 different sources, or in a defined mineral salts solution, with or without supplemental nitrogen (potassium nitrate). Decomposition rates in stream water were up to two times the rate achieved in distilled water. Experiments conducted in stream water with added mineral salts showed that the addition of either nitrogen or phosphorus stimulated carbon-14-cellulose decomposition by up to 50 per cent. A combination of nitrogen and phosphorus resulted in further enhancement (167 per cent). Nitrogen and phosphorus individually had no effect on carbon-14-lignin decomposition but simultaneous addition increased decomposition by 65 per cent. Concentrations of at least 10 mg nitrogen per litre were required for maximal lignocellulose decomposition, but concentrations above this level did not further increase the rates. Decomposition rates increased with increasing temperature over the range tested (5-22C). Ammonia accumulated in the culture filtrates of potassium nitrate supplemented incubations. The role of supplemental nitrate in lignocellulose decomposition is discussed in relation to wood decomposition and the low nitrogen concentrations in Pacific Northwest streams.