Nutrient limitation of primary production in a sub-arctic salt marsh.
In view of the use of salt marshes along the southern shores of Hudson Bay as breeding grounds and feeding areas by lesser snow geese and Canada geese, the effects of additions of nitrogen and phosphorus on net above-ground primary production were examined in a sub-arctic salt marsh in the absence of grazing. The net above-ground primary production of unfertilized vegetation (dominated by Puccinellia phryganodes and Carex subspathacea) was 65-97 g m-2 year-1, similar to published figures for other tundra communities.
Addition of nitrogen, as either ammonium or nitrate, resulted in significant increases in production, to approximately double the values for untreated vegetation. There was no significant difference in production between plots which received ammonium and those which received nitrate. Addition of phosphate did not increase net production significantly compared to untreated plots. Addition of ammonium and phosphate in combination led to much higher production than no treatment, or the addition of either ammonium or phosphate alone. It is concluded that the primary productivity of the marsh was limited by the supply of inorganic nitrogen. The supply of phosphorus was not ordinarily limiting, but became limiting when the nitrogen supply was supplemented.