Uptake kinetics and storage capacity of dissolved inorganic phosphorus and corresponding dissolved inorganic nitrate uptake in <i>Saccharina latissima</i> and <i>Laminaria digitata</i> (Phaeophyceae)

Uptake rates of dissolved inorganic phosphorus and dissolved inorganic nitrogen under unsaturated and saturated conditions were studied in young sporophytes of the seaweeds <i>Saccharina latissimi</i> and <i>Laminaria digitate</i> (Phaeophyceae) using a ‘pulse‐and‐chase’ assay under fully controlled laboratory conditions. In a subsequent second ‘pulse‐and‐chase’ assay, internal storage capacity (ISC) was calculated based on V<SUB>M</SUB> and the parameter for photosynthetic efficiency Fv/Fm. Sporophytes of <i>S. latissimi</i> showed a V<SUB>S</SUB> of 0.80±0.03 μmol · cm^-2 · d^-1and a V<SUB>M</SUB> of 0.30±0.09 μmol · cm^-2 · d^-1for DIP, while V<SUB>S</SUB> for DIN was 11.26±0.56 μmol · cm^-2 · d^-1and V<SUB>M</SUB> was 3.94±0.67 μmol · cm² · d^-1. In <i>Laminaria digitate</i>, uptake kinetics for DIP and DIN were substantially lower: V<SUB>S</SUB> for DIP did not exceed 0.38±0.03 μmol·cm−2·d^-1while V<SUB>M</SUB> for DIP was 0.22±0.01 μmol· cm^-2 · d^-1. V<SUB>S</SUB> for DIN was 3.92±0.08 μmol · cm² · d^-1and the V<SUB>M</SUB> for DIN was 1.81±0.38 μmol · cm² · d^-1. Accordingly, <i>S. latissimi</i> exhibited a larger ISC for DIP (27 μmol · cm^-2) than <i>L. digitate</i> (10 μmol · cm^-2), and was able to maintain high growth rates for a longer period under limiting DIP conditions. Our standardized data add to the physiological understanding of <i>S. latissimi</i> and <i>L. digitate</i>, thus helping to identify potential locations for their cultivation. This could further contribute to the development and modification of applications in a bio‐based economy, for example in evaluating the potential for bioremediation in integrated multi‐trophic aquacultures (IMTA) that produce biomass simultaneously for use in the food, feed and energy industries