Spatial and temporal variation in tissue halide levels of Salicornia virginica

Abstract

Succulence, tissue chloride, bromide, and iodide levels were determined in the coastal salt marsh halophyte Salicornia virginica taken from three elevations over a 12-month period. Soil samples from each sampling area were also taken for the determination of halide concentrations. The average percent dry weight (% DWt) over the 12 months and three elevations ranged from 10.8 ± 0.4 to 16.1 ± 0.3 % (± sd), with a general increase in % DWt (decrease in succulence) in tissue from all elevations peaking in September, after the dry summer, followed by a decrease in % DWt (increase in succulence) during the rainy season. The mean halide levels in S. virginica tissues over the 12 months and three elevations ranged from 17.5 to 30.3 % Cl⁻, 0.27 to 0.76 % Br⁻, and from 3.00 to 1.21 × 10⁴ ppm I⁻. Mean halide concentrations in plant water ranged from 0.66 to 1.6 M Cl⁻, 4.6 to 12 mM Br⁻ and 3.3 μM to 16 mM I⁻. No environmental factors correlated with changes in tissue halide levels. Tissue Cl⁻ levels tended to increase during the dry summer months and decrease during the wet winter months. Bromide levels were more stable. Large increases in tissue I⁻ levels were found during the months of September and October when the plants were in flower, suggesting a developmental control of I⁻ uptake. Soil concentrations of all three halides at the low elevation were consistently higher than those in the middle and high elevations. The high elevation soil Cl⁻ was the most variable of the three halides. Higher I⁻ soil levels in the low elevation during the spring/summer as compared to fall/winter probably reflect an increase in the biological and chemical reduction of IO ⁻₃ to I⁻. Tissue halide levels at the three elevations did not correlate with their respective soil concentrations. Plant water halide molar ratios were lower than in seawater and soil, indicating the selective uptake of halides in the order I⁻ > Br⁻ > Cl⁻.