The response of nutrient assimilation and biochemical composition of Arctic seaweeds to a nutrient input in summer

Abstract

Twenty-one species of macroalgae (four Chlorophyta, eight Rhodophyta, and nine Phaeophyta) from the Kongsfjord (Norwegian Arctic) were examined for their response to nutrient enrichment (nitrate and phosphate) in the summer period. The enzymatic activities related to nutrient assimilation, external carbonic anhydrase (CAext, EC 4.2.1.1), nitrate reductase (NR, EC 1.6.6.1), and alkaline phosphatase (AP, EC 3.1.3.1), as well as the biochemical composition (total C and N, soluble carbohydrates, soluble proteins, and pigments) were measured. CAext activity was present in all species, and showed a general decrease after nutrient enrichment. Inversely, NR activity increased in most of the species examined. Changes in pigment ratios pointed to the implication of light harvesting system in the acclimation strategy. Despite enzymatic and pigmentary response, the Arctic seaweeds can be regarded as not being N-limited even in summer, as shown by the slight effect of nutrient enrichment on biochemical composition. The exception being the nitrophilic species Monostroma arcticum and, to a lesser extent, Acrosiphonia sp. For the rest of the species studied, changes in total internal C and N, soluble proteins, soluble carbohydrates, pigment content, and the internal pool of inorganic N were recorded only for particular species and no general pattern was shown. Acclimation to unexpected nutrient input seemed to ensure the maintenance of a stable biomass composition, rather than an optimized use of the newly available resource (except for the nitrophilic species). This indicates a high degree of resilience of the algal community to a disruption in the natural nutrient availability pattern.

Nitrate Assimilation: The Role of In Vitro Nitrate Reductase Assay as Nutritional Predictor

“…A like inducing response, under the same conditions, has also been observed in other macroalgae (Gao, Smith & Alberte 1995;Lartigue & Sherman, 2005;Young et al, 2007;Martins et al, 2009;Cabello-Pasini et al, 2011). Nitrate reductase activity in Arctic species appears to be directly enhanced by nitrate addition, with relatively little feedback from the N-status of the cell (Gordillo et al, 2006). Communities of Laminariales species apparently possess a high degree of resilience to disruption in natural nutrient-availability patterns.…”

Climate-driven regime shifts in Arctic marine benthos

“…We conclude that the observed increases in SST and in the length of the ice-free season, leading to enhanced light conditions promoted reproduction and growth of erect, boreal macroalgae. Increased nutrient input associated with warming could have been a source of enhanced growth, but a recent nutrient enrichment study shows that macroalgae in Kongsfjord are not N-limited because they take up and store nitrogen compounds during winter (32). Along the rocky coastlines of the Arctic, boreal macroalgae are predicted to expand within the 21st century as a consequence of climate warming (21,33), an expectation that our findings support.…”

Growth and accumulation of carotenoids and nitrogen compounds in Gracilaria domingensis (Kütz.) Sonder ex Dickie (Gracilariales, Rhodophyta) cultured under different irradiance and nutrient levels

“…Concentrations of chlorophyll a in G. domingensis were not influenced by irradiance and nutrient levels and were lower than the phycobiliprotein contents. The relationship between pigment content and nutrient availability has been investigated in several studies (Jones et al, 1996;Godillo et al, 2006), indicating that Gracilaria species are able to assimilate nitrogen and, when present in excess, nitrogen is stored as proteins or pigments (Kosovel & Talarico, 1979). However, this is not the only factor determining the pigment concentrations.…”