Phosphorus transfer from sediments by Myriophyllum spicatum1

The uptake of phosphorus, the biomass, and the standing P stock were measured over the course of a year in roots and shoots of the Eurasian watermilfoil, Myriophyllum spicatum, from Lake Wingra, Wisconsin. The resulting data were used to estimate the relative contributions of root and shoot uptake to the phosphorus economy of the plant and to examine the role of the plant in moving phosphorus between sediment and water. The total yearly uptake of P by a square meter of Myriophyllum was 3.0 g P m-*. Root uptake accounted for 2.2 g, shoot uptake only 0.8 g. The rate of P release from healthy shoots was insignificant, but about 2.8 g P m-* yr-l was lost due to shoot turnover. Since most of the P uptake is by the roots and much of the plant P is transferred to and lost by the shoots, Myriophyllum is a potentially important vector in the movement ofP from the sediments to the water. The net transfer of P from the sediments to shoots of Myriophyllum in Lake Wingra is about 2.0 g P m-* yr-l. Release of this P during decay makes Myriophyllum an important source of P for pelagic phytoplankton and can explain much of the previously reported P export from the littoral zone of Lake Wingra.