An examination of essential and non-essential metals in cacao (Theobroma cacao L.) using concentrations and stable isotope compositions
File(s)
Author(s)
Barati, Elnaz
Type
Thesis
Abstract
High Cd concentrations observed in cacao beans (Theobroma cacao L.) grown in South and Central America pose global health concerns. This Ph.D. thesis aims to understand whether elements, primarily Zn and Cd, use similar mechanisms for their uptake, storage and translocation in hydroponic- and soil-cacao systems. If similar mechanisms are used for Cd and other elements, there are mitigation opportunities to reduce Cd uptake and subsequent transport to cacao beans. Firstly, using anion exchange chromatography and MC-ICP-MS, Zn isotope and concentration analyses were conducted on 19 cacao genotypes grown in hydroponic solutions under Cd stress. The results demonstrated all 19 genotypes preferentially removed isotopically light Zn from hydroponic solutions, which was also observed for Cd; and the roots were enriched in isotopically heavy Zn isotopes compared to aerial organs. This isotope partition trend between roots and aerial organs is opposite to what was observed for previously published Cd isotope data from the same plants. Secondly, using ICP-Q-MS, element concentration measurements were conducted on cacao, soil leachate and bulk soil samples from Ecuador. The results showed cacao trees had similar uptake patterns for Zn and Cd and for Mn and Cu from bioavailable pools, represented by soil leachates, indicating possible shared physiological mechanisms for uptake. Additionally, based on the concentration analyses and elemental distributions for cacao fruit, leaves, woody biomass and roots, the elements fell into three primary groups: Zn, Cd, Mg, Al, and Fe; Cu, Mn, As and Mo; and Co and Ni. Lastly, a critical review on Zn and Cd isotope fractionation in plant systems demonstrated that most plant species: preferentially take up isotopically light Zn and Cd from nutrient mediums; and isotopically heavy Zn and light Cd are sequestered in the root, whereas isotopically light Zn and heavy Cd are preferentially translocated from the root to aerial organs.
Version
Open Access
Date Issued
2023-06-02
Date Awarded
2024-03-01
Copyright Statement
Creative Commons Attribution NonCommercial NoDerivatives Licence
Advisor
Rehkämper, Mark
Moore, Rebekah
Publisher Department
Earth Science and Engineering
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)