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The Ecotone Between Spartina Foliosa Trin. and Salicornia Virginica L. in Salt Marshes of Northern San Francisco Bay: II. Soil Water and Salinity

Bruce E. Mahall and Roderic B. Park
Journal of Ecology
Vol. 64, No. 3 (Nov., 1976), pp. 793-809
DOI: 10.2307/2258809
Stable URL: http://www.jstor.org/stable/2258809
Page Count: 17
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Since scans are not currently available to screen readers, please contact JSTOR User Support for access. We'll provide a PDF copy for your screen reader.
The Ecotone Between Spartina Foliosa Trin. and Salicornia Virginica L. in Salt Marshes of Northern San Francisco Bay: II. Soil Water and Salinity
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Abstract

On two transects perpendicular to and crossing the ecotone between Spartina foliosa and Salicornia virginica measurements were made of soil water content (water as percentage of soil volume) and salt content (osmotically active solutes per unit soil volume). Values were derived for the apparent salinity of the soil solution (m-osm. g-1 water). During the rainless late spring and summer growing season the apparent salinity in the upper-littoral Salicornia zone at a depth of 0-35 cm was of the order of 0.25 m-osm. g-1 water greater than that in the mid-littoral Spartina zone. The mean values increased during the summer and by early autumn reached 1.1-1.4 m-osm. g-1 water in the Salicornia zone but only 0.85-1.1 m-osm. g-1 water in the Spartina zone. The differences between the zones became insignificant during the winter rainy season, when the plants are essentially dormant. Apparent salinities measured at the end of winter were about 0.55 m-osm. g-1 water less than those measured at the end of the preceding summer. During the summer apparent salinity decreased with depth, with differences between the 0-5 cm and 25-35 cm samples ranging from 0.20 to 0.70 m-osm. g-1 water. This gradient was reversed in the wet winter, with differences between the 0-5 cm and 25-35 cm samples ranging from 0.10 to 0.60 m-osm. g-1 water. From these measurements and those of above- and below-ground biomass it is clear that Salicornia occupies a habitat with considerably higher apparent soil salinity than that of Spartina during the growing season. Hydroponic experiments show that S. foliosa plants are less tolerant of rapid salinity changes, and their growth is much more inhibited by higher root medium salinities than is that of Salicornia virginica plants. The growth of the Spartina was severely reduced at salinities above 0.6 m-osm. g-1 water, whereas the growth of Salicornia was not significantly inhibited by salinities up to 1.4 m-osm. g-1 water and its roots seemed to be very effective at excluding ions supplied in root media with high NaCl contents. Spartina was relatively ineffective at excluding such ions and its water use efficiency declined markedly with increasing salinity while that of Salicornia increased slightly. Thus the high apparent salinities in the salt marsh Salicornia zones during the growing season appear to be sufficient to exclude Spartina.

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