Experimental determinations of soil copper toxicity to lettuce (Lactuca sativa) growth in highly different copper spiked and aged soils

Christiansen, Karen S.; Borggaard, Ole K.; Holm, Peter E.; Vijver, Martina G.; Hauschild, Michael Z.; Peijnenburg, Willie J. G. M.

Experimental determinations of soil copper toxicity to lettuce (Lactuca sativa) growth in highly different copper spiked and aged soils

2015

Accurate knowledge about factors and conditions determining copper (Cu) toxicity in soil is needed for predicting plant growth in various Cu-contaminated soils. Therefore, effects of Cu on growth (biomass production) of lettuce (Lactuca sativa) were tested on seven selected, very different soils spiked with Cu and aged for 2 months at 35 °C. Cu toxicity was expressed as pEC₅₀(Cu²⁺), i.e., the negative logarithm of the EC₅₀(Cu²⁺) activity to plant growth. The determined pEC₅₀(Cu²⁺) was significantly and positively correlated with both the analytically readily available soil pH and concentration of dissolved organic carbon [DOC] which together could explain 87 % of the pEC₅₀(Cu²⁺) variation according to the simple equation: pEC₅₀(Cu²⁺) = 0.98 × pH + 345 × [DOC] − 0.27. Other soil characteristics, including the base cation concentrations (Na⁺, K⁺, Ca²⁺, Mg²⁺), the cation exchange capacity at soil pH (ECEC), and at pH 7 (CEC₇), soil organic carbon, clay content, and electric conductivity as well as the distribution coefficient (Kd) calculated as the ratio between total soil Cu and water-extractable Cu did not correlate significantly with pEC₅₀(Cu²⁺). Consequently, Cu toxicity, expressed as the negative log of the Cu²⁺activity, to plant growth increases at increasing pH and DOC, which needs to be considered in future management of plant growth on Cu-contaminated soils. The developed regression equation allows identification of soil types in which the phytotoxicity potential of Cu is highest.

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