The Effect of Salinity on the Leaf and Shoot Demography of Two Arctic Forage Species

Abstract

1 Two important graminoid forage species, Puccinellia phryganodes and Carex subspathacea, which are eaten by lesser snow geese, are widespread in arctic coastal salt marshes. Extensive grubbing of these plants by geese has led to increased soil salinity which may restrict their regrowth, particularly for the sedge which grows in less saline sites. 2 The effects of salinity on leaf and shoot birth and death rates and on mortality of plants of the two species were therefore examined when pot-grown plants of Puccinellia were exposed to different salinities under field conditions at La Perouse Bay, Manitoba. A similar experiment on Puccinellia was also conducted in a growth chamber. 3 Leaf death rates increased with salinity and approached or exceeded leaf births at the highest salinities (40-80 g L` dissolved salts containing sodium at a concentration between 568 mol m-3 and 1136 mol m-3). The salinities at which these changes were evident depended on the species and the growing conditions. When birth and death rates of leaves and plant deaths were compared, Puccinellia phryganodes was less saltsensitive than Carex subspathacea. 4 As salinity increased, the decline in numbers of leaf births on axillary shoots and attached tillers of plants of Puccinellia and Carex was faster than the decline in leaf births on main shoots. 5 The growth responses of the two species to salinity are discussed in relation to the foraging activities of the geese and the long-term changes occurring in salt marshes on the coast of Hudson Bay.