Effect of nitrogen and silicate enrichment on photosynthate allocation by ice algae from Resolute Passage, Canadian Arctic

Enrichment experiments with ammonium, nitrate and silicate were conducted to determine their effects on the photosynthate allocation by ice algae collected during the spring of 1992 from Resolute Passage, Canadian Arctic. Ammonium concentrations of 100 μM inhibited the synthesis of protein, which was the largest fraction in the end products for the ammonium and nitrate enrichment experiments. No inhibition was detected for up to 200 μM of added nitrate. Silicate enrichment of>5 μM combined with 50 μM ammonium increased photosynthate allocation to protein to more than 45%. However, protein synthesis showed no regular pattern of increase or decrease with enrichments of varying concentration of silicate plus 50 μM of nitrate. The dominant fraction in the silicate plus nitrate experiment was polysaccharide and nucleic acids, which accounted for more than 35% of the total photosynthesis. The total lipid fraction was only slightly affected by nitrogen or silicate, but neutral lipids decreased while membrane-associated polar lipids increased with silicate plus ammonium enrichment. Our findings indicate that ice algae in Resolute Passage were likely limited by ammonium and silicate during the declining period of the algal bloom in 1992.