Nitrogen Uptake by Porphyra purpurea: its Role as a Nutrient Scrubber

Aspects of the nutrient-uptake physiology of Porphyra dioica (Brodie et Irvine) from Porto, Portugal were investigated under laboratory conditions. The capacity for uptake and accumulation of nitrogen (N) by P. dioica was determined for two different N sources, ammonium  and nitrate (). The influence of the light–dark cycle and of the simultaneous presence of  and , as well as the effects of phosphorus (P) enrichment, on the growth, nutrient uptake, and accumulation were also evaluated. Porphyra dioica was able to take up, accumulate, and grow equally well using both sources of nitrogen when presented separately. The photosynthetic pigment levels increased significantly with the increase of the availability of N, for both sources. The chlorophyll a content was higher in thalli that used  as source of N, while this difference was not seen for phycobiliprotein content. When both N sources were available (NO3 : NH4 = 6 : 1), P. dioica preferentially removed , with a clear diurnal difference. During the light period, the algae removed 70% of the  available, while only 35% was removed during the dark period. Phosphorus enrichment did not influence the growth rate or the amount of P removed from the medium, suggesting a limited capacity to store P. These results indicate that P. dioica is a good candidate for application in an integrated multi-trophic aquaculture (IMTA) system.