Identifying the species of copper that are toxic to plant roots in alkaline nutrient solutions |
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Authors: | Wang Peng Menzies Neal W Wang Yi-Min Zhou Dong-Mei Zhao Fang-Jie Kopittke Peter M |
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Institution: | 1.Key Laboratory of Soil Environment & Pollution Remediation, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China ;2.School of Agriculture and Food Sciences, The University of Queensland, St. Lucia, Queensland, 4072, Australia ;3.Rothamsted Research, Harpenden, Hertfordshire, AL5 2JQ, UK ;4.College of Resources and Environmental Sciences, Nanjing Agricultural University, Nanjing, 210095, China ; |
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Abstract: | Background and aims The pH of the growth medium influences Cu speciation in solution, the negativity of plasma membrane (PM) surface potential, and hence the rhizotoxicity of Cu. MethodsSolution culture experiments were conducted with wheat (Triticum aestivum L.) seedlings to examine the toxicity of various Cu species at pH values ranging from 4.50 to 8.25. The toxic species of Cu was identified, giving particular consideration to the electrical properties at the plant cell membrane and ion activities at the PM surface. ResultsThe solution culture studies showed that at pH?<?6.60 (i.e., free Cu2+ >95 % of total Cu), the addition of cations (Ca2+ or H+) decreased the toxic effects of Cu by decreasing the negativity of the PM surface potential (and hence decreasing the activity of Cu2+ at the PM surface). For solutions with pH values from 7.50 to 8.25 (CuCO
03
>50 % of total Cu), an increase in pH significantly enhanced the toxicity of Cu, whilst the addition of Ca had negligible influence on toxicity. ConclusionsRoot growth in solution cultures was influenced primarily by the surface activities of free Cu2+ and CuCO
03
. Across all experiments, the data indicate that it was CuCO
03
, rather than CuOH+, that contributed Cu toxicity over pH?>?7.00. Although our data do not explore the mechanism of toxicity, we propose that CuCO
03
has an important role in Cu rhizotoxicity in alkaline growth media. |
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