Stress tolerance of five willow clones after irrigation with different amounts of landfill leachate.

Short-rotation willow (Salix sp.) coppice, a commercial crop grown for energy purposes, is used for phytoremediation of landfill leachate in Sweden. However, the leachate's chemical composition can cause plant damage mainly due to high NaCl and NH4 concentrations. A pot experiment was conducted in order to quantify the growth responses of five different willow clones ("78-183", "Jorr", "Loden", "Olof", "Tora") to irrigation with different leachate mixtures (corresponding to 240, 180, and 120 mg Cl l(-1)) and to assess the applicability of leaf length and leaf fluctuating asymmetry as stress indicators. A series of plant traits (shoot, root and leaf dry weight, leaf area, leaf length and leaf fluctuating asymmetry) were measured. The irrigation with leachate resulted in reduced relative growth rates but there were no clear differences between the different concentrations. The clones "Jorr" and "Loden" performed best in terms of differences in relative growth rate between control and leachate treatments. Leaf length appeared to be a useful stress diagnostic tool for use in situ showing a high correlation to growth, whereas fluctuating asymmetry showed no such correlation. Higher N, lower P and higher Na concentrations in plant stems treated with leachate than control plants were observed.