Culturing of stoneworts and submersed angiosperms with phosphate uptake exclusively from an artificial sediment

Summary 1. We aimed to demonstrate reproducible nutrition and growth of macrophytes in non-axenic laboratory cultures preventing growth of phytoplankton and epiphytes. 2. Macrophyte shoot segments were planted in a mixture of commercial acid-washed silica sand with crystalline tricalcium phosphate, and this artificial sediment was covered with a layer of pure silica sand. The liquid mineral media used did not contain phosphorus but were rich in all other nutrient elements. A CO2 reservoir provided sustainable CO2 supply to macrophyte cultures by gas diffusion through a polyethylene membrane. 3. Chara hispida, Chara tomentosa, Chara baltica, Elodea canadensis, Potamogeton pectinatus and Zanichellia palustris could be cultivated for long term without medium exchange and aeration. Microalgae growth was prevented by the absence of phosphate in the water column. Mobilisation of tricalcium phosphate and phosphate uptake by the rhizoids of C. hispida enabled sustainable rapid shoot growth and increased the concentration of inorganic phosphate in the shoot dry weight by five to six times in comparison with plants cultivated on pure silica sand. A significant growth support from tricalcium phosphate was also observed for E. canadensis, but the rate of phosphate uptake by the roots was not sufficient to maintain a storage pool of inorganic phosphate (Pi) in the growing shoots of this plant. 4. Membrane-controlled CO2 supply from a reservoir and artificial sediments like the one described provide attractive options for the laboratory culture of macrophytes.