Significance of sedimentary phosphorus to a rooted submersed macrophyte (Najas flexilis (Willd.) Rostk. and Schmidt) and its algal epiphytes

Epiphytic participation in the open-water P cycle, ultimately helps to sustain the apparently independent P cycle of rooted macrophytes, by increasing P deposition as littoral sediment.

Abstract

Seedlings of a submersed angiosperm were grown to mature size in small, calcareous sediment-water systems labelled with radiophosphorus to reveal long-term patterns of phosphorus uptake, translocation to shoots, and utilization by algal epiphytes. Shoots of Najas flexilis (Willd.) Rostk. and Schmidt derived P almost exclusively from the sediment (>99%) and released P only sparingly to epiphytes and water (c. 2% of cumulative uptake after 5 weeks). Release of P averaged 3.5 μg P g−1 shoot dry wt (DW) day1. Release was independent of shoot P concentrations over the range 0.12–0.54% DW, which was induced by varying P availability to roots. Nuclear track microautoradiography using 33P was applied to compare utilization of macrophyte-derived P by several epiphytic taxa. Filamentous Mougeotia and long-stalked Gomphonema depended more on the external, P-poor lakewater medium than did small adnate forms like Achnanthes (respectively 20 and 60% of cell P from the host macrophyte). Epiphytic participation in the open-water P cycle, ultimately helps to sustain the apparently independent P cycle of rooted macrophytes, by increasing P deposition as littoral sediment.