Nutrient limitation of Myriophyllum spicatum growth in situ

SUMMARY. 1. The hypothesis that the submersed macrophyte biomass in natural weedbeds is nutrient limited was tested in situ by an enrichment experiment. 2. The response of Myriophyllum spicatum was significant and positive for N‐enrichment, resulting in a 30–40% increase in biomass over controls. There was no response to phosphorus or to potassium enrichment. 3. Plant length and number of shoots per rephcate were also significantly increased by nitrogen additions but again showed no response to phosphorus and potassium. 4. Water depth differences were also found to affect the plant responses in some cases. 5. The macrophyte response to fertilization was similar to that recorded for emergent macrophytes and terrestrial crops but much smaller than for phytoplankton.