THE EFFECT OF SALINITY ON THE LEAF AND SHOOT DEMOGRAPHY OF 2 ARCTIC FORAGE SPECIES

1 Two important graminoid forage species, Puccinellia phryganodes and Carer subspathacea, which are eaten by lesser snow geese, are widespre ad in arctic coastal salt marshes. Extensive grubbing of these plants by geese has led to increased soil salinity which may restrict their r egrowth, 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 experime nt 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(-1) dissolved salts containing so dium at a concentration between 568 mol m(-3) and 1136 mol m(-3)). The salinities at which these changes were evident depended on the specie s and the growing conditions. When birth and death rates of leaves and plant deaths were compared, Puccinellia phryganodes was less salt-sen sitive than Carer subspathacea. 4 As salinity increased, the decline i n numbers of leaf births on axillary shoots and attached tillers of pl ants of Puccinellia and Carer was faster than the decline in leaf birt hs on main shoots. 5 The growth responses of the two species to salini ty are discussed in relation to the foraging activities of the geese a nd the long-term changes occurring in salt marshes on the coast of Hud son Bay.