Epiphytic alkaline phosphatase on natural and artificial plants in an oligotrophic lake: Re‐evaluation of the role of macrophytes as a phosphorus source for epiphytes

Abstract

Alkaline phosphatase activity (APA) and Chl a concentrations of epiphytes were measured from two species of aquatic macrophytes (Potamogeton illinoensis and Scirpus subterminalis) and structurally similar artificial plants in a P‐limited lake. The artificial substrata were incubated serially in situ to simulate the age of the natural plant leaves. Throughout the macrophyte growing season, APA per unit of algal Chl on both new and aging leaves was consistently greater for intact epiphytes on artificial plants. This enhancement increased 2‐fold to 20‐fold (mean 4.5‐fold and 7.4‐fold for epiphytes from natural and artificial plants) when epiphytes were removed from the plants and suspended before enzymatic assay, exposing more algal cells to the amended PO43− substrate. Comparisons of APA for epiphytes on natural and artificial plants indicated that in this oligotrophic lake, submersed macrophytes were a source of P for epiphytes throughout the growing season and significantly influenced the P metabolism of the microflora. Epiphyte Chl was significantly greater from artificial than from natural plants in 6 of 11 comparisons, however, perhaps indicating a trade‐off between improved P availability and some nonbeneficial factor associated with the macrophyte.