Copper phytoextraction with Salix purpurea × viminalis under various Ca/Mg ratios. Part 2. Effect on organic acid, phenolics and salicylic acid contents

Abstract

One-year-old cuttings of basket willow (Salix purpurea × viminalis) were cultivated hydroponically under increasing Cu concentrations (0, 1, 2 and 3 mM) and at four Ca/Mg ratios (4:1, 1:10, 20:1 and 1:1/4). After 14 days, rhizosphere and leaf samples were analysed. Salix plants were able to release relatively high amounts of low molecular weight organic acids (LMWOAs) in a short period of time. The total amount of LMWOAs increased with increasing Cu concentrations. Oxalic and acetic acids were dominant, and act as complexing agents for Cu ions, and therefore, organic exudates should be taken into account in phytoextraction of polluted areas. The Ca/Mg ratio of the medium significantly influenced not only concentration, but also the composition of LMWOAs. Phenolics content in leaves increased with the excess of Ca and Mg and with Cu level in the medium for all Ca/Mg ratios. The accumulation of glucose, fructose and sucrose in leaves was observed for deficiency and excess of Ca and/or Mg and Cu treatment at all Ca/Mg ratios. Excess calcium (Ca/Mg = 20:1) led to strong induction of salicylic acid biosynthesis, probably resulting from enhanced oxidative stress. © 2013 The Author(s).