Relative Importance of Ion Exclusion, Secretion and Accumulation in Spartina alterniflora Loisel.

The extent to which Spartina alterniflora Loisel. excluded,secreted or accumulated the major seawater ions (Cl^-, SO^2-₄,Na⁺, K⁺, Mg²⁺, and Ca²⁺) was investigated under varying salinitytreatments. From a quantitative viewpoint, ion exclusion wasmost prominent and accounted for 91–97% of the theoreticalmaximum ion uptake as a result of transpiration and growth.Of those ions taken up, approximately half was secreted fromthe shoots. Relative to K⁺, a disproportionate amount of Na⁺was excluded at the roots and secreted by the shoots. The concentrationwithin the tissues of S. alterniflora did not change with salinitytreatment for the majority of the ions examined, but Na⁺ wasmore than twice as concentrated at 40 g dm^-3 than at lOgdm^-3.Calculations of the flux of ions from salt marsh sediments tothe flood water via shoot secretion or stem/leaf turnover indicatethat these processes may be important to the ecology of S. alternifloraas mechanisms that limit the accumulation of salt within theroot zone.