Excretion of ions (Cd2+, Li+, Na+ and Cl−) by Tamarix aphylla

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Abstract
Excretion of minerals by the NaCl‐resistant and comparatively cadmium‐resistant tree Tamarix aphylla (L.) Karst, was investigated. Cd2+ was excreted by plants exposed for 1–10 days to 9 or 45 μM Cd2+ solutions. Excretion of this toxic ion increased considerably with time but was less than 5% of the quantities that had been accumulated in the shoots. Excretion of Na+ and Cl− was positively correlated with NaCl concentration (1.5, 10, 50 mM) of the medium. The Na+/Cl− ratios of the excrete were positively correlated with the concentration of the treatment solution. Ca2+ excretion decreased with increasing NaCl concentrations of the solution. Excretion of K+ and Mg2+ was only little affected by NaCl. Excretion of Li+ occurred whenever this element was supplied in the uptake solution; daily excretion rates of Li+ increased with time. The ecological significance of excretion is discussed in relation to the low selectivity of the mechanism in T. aphylla.