HR: 10:50h
AN: B12A-03    [Abstracts]
TI: Zinc Isotopes in the Soil-Plant Interface
AU: * Arnold, T
EM: tim.arnold@imperial.ac.uk
AF: Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, UK, SW7 2AZ, United Kingdom
AU: Weiss, D
EM: d.weiss@imperial.ac.uk
AF: Department of Earth Science and Engineering, Imperial College London, South Kensington Campus, UK, SW7 2AZ, United Kingdom
AU: Weiss, D
EM: d.weiss@imperial.ac.uk
AF: Department of Mineralogy, The Natural History Museum, Cromwell Road, London, SW7 5BD, United Kingdom
AU: Wissuwa, M
EM: wissuwa@affrc.go.jp
AF: Japan International Research Center for Agricultural Sciences, Crop Production and Environment Division, Tsukuba, Ibaraki, 305–8686, Japan
AU: Zhao, F
EM: fangjie.zhao@bbsrc.ac.uk
AF: Agriculture and Environment Division, Rothamsted Research, Harpenden, AL5 2JQ, United Kingdom
AU: Kirk, G
EM: g.kirk@cranfield.ac.uk
AF: National Soil Resources Institute, Cranfield University, Silsoe, MK45 4DT, United Kingdom
AB: From the geosphere/biosphere system as a whole down to the organism and cellular level, isotopes have the potential capability to uniquely understand the fluxes of inorganic elements. Zinc is of particular interest as it is one of the trace elements essential for living organisms and most usefully its chemistry is simplified by the possession of only one oxidised state (II). The use of multicollector ICP-MS, together with complete sample digestion and anion exchange chromatography, has allowed the measurement of Zn isotopes to be made precisely (below ±0.1‰ (2 S.D., n=4 typically)) and accurately in the geological and biological matrices studied. Zinc deficiency is the most widespread micronutrient disorder in rice (\it Oryza \it sativa) and differences between genotypes render some genotypes more susceptible to deficiency than others. Hence rice was chosen as a model species in our uptake and fractionation studies. A previous hydroponic study in our laboratory showed Zn uptake by tomato, lettuce and rice all produced an enrichment of the light Zn isotopes in plant shoots. A study of vegetation in a watershed, however, revealed a more complex picture, and plant shoots and roots were generally enriched in heavy isotopes relative to the litter and superficial soils. In the results presented here, rice grown under field conditions showed only heavy or insignificant fractionations relative to the soil matrix (in contrast to the hydroponic study). A genotype tolerant to Zn soil deficiency (line 46) and a genotype intolerant to deficiency (IR74) were grown in both zinc fertilised and unfertilised (Zn deficient) plots as part of a larger study. On the zinc fertilised plots, shoot samples of both genotypes showed a negligible difference in δ⁶⁶Zn_IMP-Zn compared to the growth soil. On unfertilised plots (soil δ⁶⁶Zn_{IMP- Zn} = 0.14 ± 0.10 ‰ (2 S.E., n=3)), however, line 46 rice showed preferential heavy uptake (δ⁶⁶Zn_IMP-Zn = 0.35 ± 0.04 ‰ (2 S.E., n=4)) compared to IR74 (δ⁶⁶Zn_IMP-Zn = 0.22 ± 0.07 ‰ (2 S.E., n=4)). The most likely explanation for a heavy signature is that of an equilibrium reaction induced in the zinc deficient soil environment. It has been hypothesised by plant scientists that under Zn limiting conditions, plants may secrete complexing agents that bind Zn²⁺ outside the plant and that it is these complexes that are then taken up across the cell membrane. It has been difficult to prove such a hypothesis due to the inherent problems of conducting experiments under normal Zn deficient conditions; however, new isotope studies such as these promise to provide additional insight.
UR: http://www3.imperial.ac.uk/earthscienceandengineering/people/phdstudents/a-b/arnoldt
DE: 0454 Isotopic composition and chemistry (1041, 4870)
SC: Biogeosciences [B]
MN: 2007 Fall Meeting