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Soil salinity and moisture gradients and plant zonation in Mediterranean salt marshes of Southeast Spain

For two years, we measured soil moisture, pH, salinity, and ion concentrations bimonthly from 55 vegetation plots in six Mediterranean salt marshes of SE Spain. Edaphic characteristics during dry and wet seasons were compared within six selected plant communities. The dominant species in each of these communities were Suaeda vera, Lygeum spartum, Limonium sp, Sarcocornia fruticosa, Halocnemum strobilaceum, and Arthrocnemum macrostachyum. Although soil salt concentrations were lower during the wet season, different patterns of temporal variation in total dissolved salts, sodium adsorption ratio, Cl−, Na+, K+, Ca2+, and Mg2+ were observed in the soils occupied by different plant communities. The variation patterns for SO42− were the same in all plant communities. The Ca2+/Mg2+, Ca2+/Na+, and SO42−/Cl− ratios increased during the wet season because of the more pronounced decrease in Cl−, Na+, and Mg2+ concentrations relative to Ca2+, and SO42−. Canonical correspondence analysis (CCA) related the species distribution with certain soil conditions. The edaphic variables that best explained the data were maximum soil moisture, mean K+/Na+ ratio, mean Ca2+/Mg2+ ratio, maximum pH, and maximum K+. Two different environments were identified: dry salt marsh and wet salt marsh. to examine soil ionic gradients in these two environments, two further CCA were applied. The variables that best explained soil-vegetation relationships in the dry salt marsh were mean K+/Na+ ratio, mean Ca2+/Mg2+ ratio, maximum K+, and minimum Ca2+/Na+ ratio. Some representative dry salt marsh species were Lygeum spartum, Atriplex glauca, Suaeda vera, and Frankenia corymbosa. The variables explaining the data set in the wet salt marsh were maximum sodium adsorption ratio, maximum Mg2+ content, mean Ca2+ content, and mean Ca2+/Mg2+ ratio. Species such as Arthrocnemum macrostachyum, Sarcocornia fruticosa, Juncus maritimus, and Tamarix boveana were representative of this environment.