Difference characteristics of phosphorus in Chara and two submerged angiosperm species: implications for phosphorus nutrient cycling in an aquatic ecosystem

Abstract

Phosphorus speciation in three submerged macrophytes species, Chara fibrosa Agardh ex Bruzelius, Najas marina Linnaeus and Vallisneria gigantea Graebner, and the implications for phosphorus nutrient cycling in an aquatic ecosystem were studied, using sequential phosphorus fractionations. The results showed that C.␣fibrosa had a far higher residual ash and calcium content compared with the two angiosperm species, but lower total phosphorus content. Two different fractionation methods for phosphorus showed that the bioavailable water-soluble phosphorus (H2O-P) and ammonium chloride extractable phosphorus (NH4Cl-P) of the extractions used represented the major part of total plant phosphorus in the two angiosperm species, while organic phosphorus (NaOH-P) represented a relatively large fraction in C. fibrosa. In this species, about 12–15% of total plant phosphorus was calcium-bound phosphorus (HCl-P), occurring as co-precipitation with calcite encrustation, but this fraction was negligible in the two angiosperm species, i.e. less than 1%. The redox-insensitive forms of HCl-P are considered less bioavailable and not affected by anoxic conditions of bottom sediment, thus have potential as a phosphorus nutrient sink in aquatic ecosystems.