Facilitation of phosphate assimilation by aquatic mycorrhizae of Vallisneria americana Michx

Presence of vesicular-arbuscular mycorrhizal fungi was found toenhance phosphate uptake in the submersed plant Vallisneriaamericana compared with plants treated with a fungicidal medium(i.e., Captan). Incorporation of 33P-orthophosphate into roottissue in short-term incubations was over 85% greater for plantswith active mycorrhizae. In addition, we measured a fine-scale irongradient and elevated concentrations of solid-phase phosphate in theextensive sheath surrounding the roots. The coupling of fungalsymbionts with phosphorus storage in the sheath may be an importantmechanism of phosphate assimilation in submersed aquatic macrophytes.Contrary to the effect on phosphate uptake, we did not find that15NH4 assimilation by Vallisneria americanaroots wasenhanced by the presence of the mycorrhizal association.