Water Use and Salt Balance in Three Salt Marsh Succulents

Water-use characteristics and potential salt accumulation rates were studied in three halophytes, Salicornia virginica, Balis marítima and Borrichia frutescens, inhabiting a salinity gradient in the high marsh. Xylem pressure potential (ψρ), leaf osmotic potential (ψπ) and leaf relative water content were measured seasonally in the three species. Species growing on the high end of the salinity gradient developed more negative xylem pressure potentials compared to species growing at lower soil salinities. This trend was also observed for leaf osmotic potentials. Low mean leaf ψπ (below –15 to –36 bars) and high ash contents (0.27–0.48 g NaCl/g DW) indicated salt accumulation in transpiring tissues. However, calculations of potential salt accumulation, based on rates of transpiration and substrate salinity, suggest that some mechanism of salt exclusion at the roots may be operating.