Relationships between spatio-temporal changes in the sedimentary environment and halophytes zonation in salt marshes

This study reports the soil-plant relationships along the intertidal gradient from unvegetated mudflats to the ecotone between high marshes and coastal dunes. The main objective was to establish the integrated role of spatial and seasonal changes in the sedimentary abiotic environment in relation to the establishment of the halophytes zonation pattern. The sedimentary environment and the halophytes coverage were sampled bimonthly during a year in nine intertidal habitats characterized by different plant communities. The highest values of sediment water content (40-60%) and electrical conductivity (20-30 mS cm(-1)) were registered in low middle marshes, the highest organic matter content (ca. 23%) was found in middle marshes, and the highest pH (8.5-9.0) was recorded in high marshes. The conductivity and the pH of the marsh sediments changed seasonally. The sediment conductivity reached its highest values during spring and summer. The spatial variations in the sedimentary environment were closely associated with the distribution of most of the recorded halophytes, especially in low and high marshes where the abiotic environment was more stressful. At the same time, cyclical seasonal changes in conductivity seemed to determine the distribution of the halophytes in high marshes, where the seasonality was very marked under Mediterranean climate. The combination and integration over time of these spatio-temporal changes in the sedimentary environment defined habitats with contrasted abiotic conditions parallel to the tidal line and complex abiotic mosaics inside some of these habitats, allowing the cohabitation of > 30 plant species along the intertidal gradient.