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Cadmium Isotope Fractionation in Soil–Wheat Systems
journal contribution
posted on 2016-08-02, 00:00 authored by Matthias Wiggenhauser, Moritz Bigalke, Martin Imseng, Michael Müller, Armin Keller, Katy Murphy, Katharina Kreissig, Mark Rehkämper, Wolfgang Wilcke, Emmanuel FrossardAnalyses
of stable metal isotope ratios constitute a novel tool
in order to improve our understanding of biogeochemical processes
in soil–plant systems. In this study, we used such measurements
to assess Cd uptake and transport in wheat grown on three agricultural
soils under controlled conditions. Isotope ratios of Cd were determined
in the bulk C and A horizons, in the Ca(NO3)2-extractable Cd soil pool, and in roots, straw, and grains. The Ca(NO3)2-extractable Cd was isotopically heavier than
the Cd in the bulk A horizon (Δ114/110Cdextract–Ahorizon = 0.16 to 0.45‰). The wheat plants were slightly enriched
in light isotopes relative to the Ca(NO3)2-extractable
Cd or showed no significant difference (Δ114/110Cdwheat–extract = −0.21 to 0.03‰). Among
the plant parts, Cd isotopes were markedly fractionated: straw was
isotopically heavier than roots (Δ114/110Cdstraw–root = 0.21 to 0.41‰), and grains were heavier than straw (Δ114/110Cdgrain–straw = 0.10 to 0.51‰).
We suggest that the enrichment of heavy isotopes in the wheat grains
was caused by mechanisms avoiding the accumulation of Cd in grains,
such as the chelation of light Cd isotopes by thiol-containing peptides
in roots and straw. These results demonstrate that Cd isotopes are
significantly and systematically fractionated in soil–wheat
systems, and the fractionation patterns provide information on the
biogeochemical processes in these systems.