Effects of nutrients and temperature on decomposition of <i>Myriophyllum spicatum</i> L. in a hard‐water eutrophic lake1

Abstract

Temperature, phosphorus, and nitrogen were investigated as possible factors influencing decay of Myriophyllum spicatum shoots. In laboratory experiments, nitrogen enrichment significantly increased decay rates while phosphorus enrichment did not. Similar increases in decay rate per unit of added nitrogen occurred whether nitrogen was provided as nitrate or was present as additional tissue nitrogen. Exponential decay coefficients depended on temperature with a Q 10 of about 3. Predictions of decay rates during litter bag experiments were based on laboratory responses of decay rate to temperature and initial nitrogen concentration of the shoots. Observed decay rates correlated closely with predictions, demonstrating the usefulness of temperature and shoot nitrogen content in explaining variations in decay rates in Lake Wingra. However, predictions underestimated decay rates. Possible explanations for the discrepancies include slow establishment of the detrital microflora, lower nitrogen availability, and absence of animals in the laboratory incubations.