Towards an understanding of the Cd isotope fractionation during transfer from the soil to the cereal grain

Cadmium isotope fractionation in the soil – cacao systems of Ecuador: a pilot field study

“…Furthermore, Cd isotope data for numerous different mineral P fertilizers reveal that the great majority are characterized by d 114/110 Cd values of less than 0.20&. [33][34][35] Use of such fertilizers in the more distant past is thus unlikely to have caused the observed high d 114/110 Cd ¼ 0.24& for the 0-5 cm topsoil at Site A-2 ( Fig. 2 and Table 2).…”

“…57 Of further interest in this context are recent detailed studies of soil-wheat agricultural systems in Switzerland, which also identied Cd enrichments characterized by heavy isotope compositions in topsoils. 31,33 Based on a detailed soil mass balance, it was concluded that these Cd enrichments are unlikely to be of recent origin but rather reect long-term 'plantpumping', whereby uptake of Cd by plants and trees, subsequent decay of the organic matter with relatively high d 114/110 Cd and release of this Cd into the topsoil over long timescales is responsible for the Cd enrichment. In the absence of a detailed soil mass balance for the cacao sites of this study, it is therefore uncertain whether the observed topsoil Cd enrichments have a long-term origin, which predates cacao cultivation or reect recent agricultural practices, such as the use of leaf litter as a soil supplement.…”

“…31 In part, this isotopic difference reects that the plant-available (PA) Cd pool of soils typically appears to be characterized by higher d 114/110 Cd than bulk soils, with a fractionation factor of up to D 114/110 Cd PAsoil z 0.5&. 31,33 As such, bulk wheat plants have Cd isotope compositions that closely resemble the plant-available Cd of soils but with signicant internal Cd isotope fractionation, whereby successively higher d 114/110 Cd values are observed for the roots, the straw and the grains. Amongst these compartments, only the grains are consistently enriched in isotopically heavy Cd relative the plant-available soil Cd, with an apparent fractionation of D 114/110 Cd PA-grain z 0.1-0.5&.…”

“…Such studies have already shown, however, that coupled Cd concentration and isotope data can be used to trace the origin of isotopically distinct Cd inputs, such as mineral P fertilizers, into soils. [31][32][33][34][35] In addition, isotope data can provide constraints on the distinct cellular and molecular processes that are employed by plants for the uptake, internal transport and sequestration of Cd. In particular, recent publications demonstrated that wheat and barley display similar trends of Cd isotope fractionation 33 and these differ signicantly from the isotope systematics observed for Cdtolerant and accumulator cultivars.…”

“…[31][32][33][34][35] In addition, isotope data can provide constraints on the distinct cellular and molecular processes that are employed by plants for the uptake, internal transport and sequestration of Cd. In particular, recent publications demonstrated that wheat and barley display similar trends of Cd isotope fractionation 33 and these differ signicantly from the isotope systematics observed for Cdtolerant and accumulator cultivars. 36 As various genotypes of cacao differ in the extent to which Cd is enriched in the plants relative to soil and in how Cd is partitioned within the plants, 7,25,30 such genotypes might also exhibit distinct Cd isotope signatures as a consequence of distinct pathways for Cd uptake, transport and sequestration.…”