Phosphorus release by submerged macrophytes: Significance to epiphyton and phytoplankton1,1

The contribution of nine species of macrophytes to the phosphorus nutrition of their epiphytes and the rates of P release by Myriophyllum spicatum L. were measured in situ on fully labeled (32P) plants. The epiphytes derived only 3.4–9.0% of their P from the supporting macrophyte, indicating that previously suggested macrophyte‐epiphyte nutrient interactions are of relatively minor importance. Although high diurnal P release rates (x̄ = 3.24 µg·g‒1·h‒1) were observed for the Myriophyllum‐epiphyte complex, Myriophyllum accounted for only 9.9% (0.32 µg·g−1·h−1) of the total P released: The Myriophyllum‐derived P was, however, released in a highly available soluble form (minimum estimate: 60.3%). During the growing season, Myriophyllum thus appears to be principally important as a physical support for an active microbial community rather than as a P source to its epiphyton and surrounding waters.