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- Nitrate reductase activity in green macroalgae as an environmental indicator of temperature and salinity changes and its implication for climate change projectionsPublication . Madeira, Hélder T.; Aníbal, Jaime; Carvalho, Liliana F.; Esteves, Eduardo; Veiga-Pires, C.Temperature and salinity changes can affect nutrient assimilation dynamics in primary producers. Green macroalgae use nitrate as a main source of nitrogen for their metabolism. Nitrate needs to be reduced by nitrate reductase, before amino acids synthesis. Our aims were to study the effect of temperature and salinity changes on nitrate reductase activity (NRA) in Ulva rigida and Enteromorpha clathrata, and to assess if this enzyme can be used as an environmental indicator for changes in such abiotic factors. The study of NRA was carried out using potassium nitrate as substrate and propanol as a membrane permeabilizer, letting the produced nitrite to exit the macroalgae cells into the assay medium, allowing its quantification through a colorimetric method. This procedure was carried out at five temperatures (10, 20, 30, 35 and 40 °C) and three salinities of the assay medium (0, 15 and 36 g/kg). Results show that both Ulva and Enteromorpha have maximum NRA at salinities of 36 g/kg, although nitrate reduction can occur in freshwater or brackish water, but at significantly lower rates. NRA varied significantly with temperature for both macroalgae, although Ulva showed maximum NRA at 30 °C, while NRA peaked at 35 °C in Enteromorpha. Likely adequate models were tentatively fitted to NRAtemperature data at different salinities. NRA is a suitable proxy of the effects of temperature and salinity changes on the ability of green macroalgae to uptake and metabolize nitrogen nutrients and can thus be the base for macroalgae proliferation models under climate change model scenarios.
- Macroalgae mitigation potential for fish aquaculture effluents: an approach coupling nitrogen uptake and metabolic pathways using Ulva rigida and Enteromorpha clathrataPublication . Aníbal, J.; Madeira, Hélder T.; Carvalho, Liliana F.; Esteves, E.; Veiga-Pires, C.; Rocha, CarlosAquaculture effluents are rich in nitrogen compounds that may enhance local primary productivity, leading to the development of algae blooms. The goal of this study was to assess the potential use of naturally occurring green macroalgae (Ulva and Enteromorpha) as bioremediators for nitrogen-rich effluents from a fish aquaculture plant, by evaluating their respective uptake dynamics under controlled conditions. Ulva and Enteromorpha were incubated separately in aquaculture effluent from a local pilot station. Algae tissue and water samples were collected periodically along 4 h. For each sample, nitrate, nitrite, and ammonia concentrations were quantified in the effluent, while internal algae reserve pools and nitrate reductase activity (NRA) were determined within the algae tissues. Both macroalgae absorbed all dissolved inorganic nitrogen compounds in less than 1 h, favoring ammonia over nitrate. Ulva stored nitrate temporarily as an internal reserve and only used it after ammonia availability decreased, whereas Enteromorpha stored and metabolized ammonia and nitrate simultaneously. These distinct dynamics of ammonia and nitrate uptake supported an increase in NRA during the experiment. This study supports the hypothesis that Ulva or Enteromorpha can be used as bioremediators in aquaculture effluents to mitigate excess of dissolved inorganic nitrogen.
- Effects of temperature and salinity on nitrate uptake by green macroalgaePublication . Madeira, Hélder Trindade; Aníbal, J.; Carvalho, Liliana Faia; Esteves, E.; Veiga-Pires, C.; Rocha, C.Temperature, salinity and the availability of dissolved inorganic nutrients are amongst the most important abiotic factors driving macroalgae produstions in estuarine and coastal ecosystems.