Uptake kinetics and storage capacity of dissolved inorganic phosphorus and corresponding N:P dynamics in Ulva lactuca (Chlorophyta)

Dissolved inorganic phosphorus ( DIP ) is an essential macronutrient for maintaining metabolism and growth in autotrophs. Little is known about DIP uptake kinetics and internal P‐storage capacity in seaweeds, such as Ulva lactuca (Chlorophyta). Ulva lactuca is a promising candidate for biofiltration purposes and mass commercial cultivation. We exposed U. lactuca to a wide range of DIP concentrations (1–50 μmol · L −1 ) and a nonlimiting concentration of dissolved inorganic nitrogen ( DIN ; 5,000 μmol · L −1 ) under fully controlled laboratory conditions in a “pulse‐and‐chase” assay over 10 d. Uptake kinetics were standardized per surface area of U. lactuca fronds. Two phases of responses to DIP ‐pulses were measured: (i) a surge uptake ( V S ) of 0.67 ± 0.10 μmol · cm −2  · d −1 and (ii) a steady state uptake ( V M ) of 0.07 ± 0.03 μmol · cm −2  · d −1 . Mean internal storage capacity ( ISC P ) of 0.73 ± 0.13 μmol · cm −2 was calculated for DIP . DIP uptake did not affect DIN uptake. Parameters of DIN uptake were also calculated: V S  = 12.54 ± 1.90 μmol · cm −2  · d −1 , V M  = 2.26 ± 0.86 μmol · cm −2  · d −1 , and ISC N  = 22.90 ± 6.99 μmol · cm −2 . Combining ISC and V M values of P and N, nutrient storage capacity of U. lactuca was estimated to be sufficient for ~10 d. Both P and N storage capacities were filled within 2 d when exposed to saturating nutrient concentrations, and uptake rates declined thereafter at 90% for DIP and at 80% for DIN . Our results contribute to understanding the ecological aspects of nutrient uptake kinetics in U. lactuca and quantitatively evaluating its potential for bioremediation and/or biomass production for food, feed, and energy.