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

Abstract

Uptake rates of dissolved inorganic phosphorus and dissolved inorganic nitrogen under unsaturated and saturated conditions were studied in young sporophytes of the seaweeds Saccharina latissima and Laminaria digitata (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_M and the parameter for photosynthetic efficiency F_v /F_m . Sporophytes of S. latissima showed a V_S of 0.80 ± 0.03 μmol · cm^-2 · d^-1 and a V_M of 0.30 ± 0.09 μmol · cm^-2 · d^-1 for dissolved inorganic phosphate (DIP), whereas V_S for DIN was 11.26 ± 0.56 μmol · cm^-2 · d^-1 and V_M was 3.94 ± 0.67 μmol · cm^-2 · d^-1 . In L. digitata, uptake kinetics for DIP and DIN were substantially lower: V_S for DIP did not exceed 0.38 ± 0.03 μmol · cm^-2 · d^-1 while V_M for DIP was 0.22 ± 0.01 μmol · cm^-2 · d^-1 . V_S for DIN was 3.92 ± 0.08 μmol · cm^-2 · d^-1 and the V_M for DIN was 1.81 ± 0.38 μmol · cm^-2 · d^-1 . Accordingly, S. latissima exhibited a larger ISC for DIP (27 μmol · cm^-2 ) than L. digitata (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 S. latissima and L. digitata, 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 multitrophic aquacultures that produce biomass simultaneously for use in the food, feed, and energy industries.

Keywords: Laminaria digitata; Saccharina latissima; nitrate uptake; phosphate uptake; uptake kinetics.