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-, SO42-, Na+, K+, Mg2+, and Ca2+) was investigated under varying salinity treatments. From a quantitative viewpoint, ion exclusion was most prominent and accounted for 91-97% of the theoretical maximum ion uptake as a result of transpiration and growth. Of those ions taken up, approximately half was secreted from the shoots. Relative to K+, a disproportionate amount of Na+ was excluded at the roots and secreted by the shoots. The concentration within the tissues of S. alterniflora did not change with salinity treatment for the majority of the ions examined, but Na+ was more than twice as concentrated at 40 g dm-3 than at 10 g dm-3. Calculations of the flux of ions from salt marsh sediments to the flood water via shoot secretion or stem/leaf turnover indicate that these processes may be important to the ecology of S. alterniflora as mechanisms that limit the accumulation of salt within the root zone.