Experimental determinations of soil copper toxicity to lettuce (Lactuca sativa) growth in highly different copper spiked and aged soils
2015
Christiansen, Karen S. | Borggaard, Ole K. | Holm, Peter E. | Vijver, Martina G. | Hauschild, Michael Z. | Peijnenburg, Willie J. G. M.
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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