UPTAKE KINETICS AND STORAGE CAPACITY OF DISSOLVED INORGANIC PHOSPHORUS AND CORRESPONDING N: P DYNAMICS IN&IT ULVA LACTUCA &IT(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 laduca (Chlorophyta). Ulva laduca is a promising candidate for biofiltration purposes and mass commercial cultivation. We exposed U. laduca to a wide range of DIP concentrations (1-50 mu mol center dot L-1 and a nonlimiting concentration of dissolved inorganic nitrogen (DIN; 5,000 mu mol center dot 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. lactual fronds. Two phases of responses to DIP-pulses were measured: (i) a surge uptake (V-s) of 0.67 +/- 0.10 mu mo] center dot cm(-2) center dot d(-1) and (ii) a steady state uptake (V-M ) of 0.07 +/- 0.03 mu mol center dot cm(-2)center dot d(-1) . Mean internal storage capacity (ISCp) of 0.73 +/- 0.13 mu mol center dot 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 mu mol center dot cm(-2) center dot d(-1), V-M = 2.26 +/- 0.86 mu mol center dot cm(-2) center dot d(-1) , and ISCN = 22.90 +/- 6.99 mu mol center dot cm(-2) . Combining ISC and V-M values of P and N, nutrient storage capacity of U. lactuca was estimated to be sufficient for similar to 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.