Nutrient Limitation of Primary Production in a Sub-Arctic Salt Marsh

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Abstract
Sub-arctic salt marshes along the southern shores of Hudson Bay [Canada] are used as breeding grounds and feeding areas by lesser snow geese [Anser caerulescens caerulescens] and Canada geese [Brauta canadensis]. The effects of additions of N and P on net above-ground primary production were examined in a sub-arctic salt marsh dominated by Puccinellia phryganodes and Carex subspathacea, to determine whether primary production (and hence forage) was limited by the availability of these elements in the absence of grazing. The net above-ground primary production of unfertilized vegetation was 65-97 g m-2 yr-1, similar to published figures for other tundra communities. Addition of N, 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 signficantly 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. The primary productivity of the marsh was limited by the supply of inorganic N. The supply of P was not ordinarily limiting, but became limiting when the N supply was supplemented.