Browsing by Author "Wu, J"

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    Coupled U-series and radiocarbon dating of a Chinese stalagmite from 15 to 33 ka: testing calibration applicability and dead carbon correction variability
    (Elsevier, 2006-08) Hodge, E; Zhao, JX; Feng, YX; Wu, J; Fink, D; Hua, Q
    A high purity stalagmite from South China with minimal detrital component (based on 230Th/232Th ratios >4000) and an average growth rate of ∼50 mm/ka has been carefully sampled along its growth axis for both U-series and radiocarbon measurements in a study to investigate its applicability for improving the database of radiocarbon calibration for the pre-dendro period (∼12.4 ka). Our preliminary assessment is based on a set of 15 high-precision AMS 14C-and 6 TIMS U-series samples spaced over the 37 cm length of the stalagmite to confirm an age range of 15 to 33 ka. TIMS U-series dates over this age range can be obtained to 0.5% at 2σ errors and as speleothems are composed of dense crystalline calcite, they are often less vulnerable to post-depositional alteration than corals. However an issue of serious concern in such an analysis is to evaluate whether the variability of the dead carbon fraction (DCF) over this time range reduces the reliability and quality of a speleothem-based calibration of atmospheric radiocarbon. The DCF represents the fraction of carbon derived from host limestone surrounding the cave that contains negligible 14C and therefore offsets the 14C date towards older ages. An assumption of a constant DCF, estimated by others to be ∼16% for speleothems (based on matching to a well-constrained radiocarbon calibration curve from 11 to 15 ka) requires case-by-case verification. Calendar ages for the positions taken for AMS 14C samples were interpolated from adjacent U-series dates on the growth curve. These absolute ages were compared to the measured AMS 14C ages and then overlain on the IntCal04 calibration curve. In broad terms, our preliminary results indicate that the growth rate, although continuous, was not linear over the period from 15 to 33 ka. In order to minimise the difference between our 14C-ages and the IntCal04 curve from 26 ka to 15.6 ka, we required an average DCF of 18%. However, this value causes the younger half (<22 ka) to be ‘too old’ and the upper section (>22 ka) to be too ‘young’ indicating that DCF over the LGM period was probably not constant. To further qualify the status of this stalagmite and decouple growth rate variability from that of the DC, a new set of 30 paired 230Th–AMS 14C-ages are in progress. Copyright © 2006 Elsevier Ltd.
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    Translocation of foliar absorbed Zn in sunflower (Helianthus annuus) leaves
    (Frontiers, 2022-03-02) Li, C; Wang, LL; Wu, J; Blamey, FPC; Wang, N; Chen, YL; Ye, Y; Wang, L; Paterson, DJ; Read, TL; Wang, P; Lombi, E; Wang, YH; Kopittke, PM
    Foliar zinc (Zn) fertilization is an important approach for overcoming crop Zn deficiency, yet little is known regarding the subsequent translocation of this foliar-applied Zn. Using synchrotron-based X-ray fluorescence microscopy (XFM) and transcriptome analysis, the present study examined the translocation of foliar absorbed Zn in sunflower (Helianthus annuus) leaves. Although bulk analyses showed that there had been minimal translocation of the absorbed Zn out of the leaf within 7 days, in situ analyses showed that the distribution of Zn in the leaf had changed with time. Specifically, when Zn was applied to the leaf for 0.5 h and then removed, Zn primarily accumulated within the upper and lower epidermal layers (when examined after 3 h), but when examined after 24 h, the Zn had moved to the vascular tissues. Transcriptome analyses identified a range of genes involved in stress response, cell wall reinforcement, and binding that were initially upregulated following foliar Zn application, whereas they were downregulated after 24 h. These observations suggest that foliar Zn application caused rapid stress to the leaf, with the initial Zn accumulation in the epidermis as a detoxification strategy, but once this stress decreased, Zn was then moved to the vascular tissues. Overall, this study has shown that despite foliar Zn application causing rapid stress to the leaf and that most of the Zn stayed within the leaf over 7 days, the distribution of Zn in the leaf had changed, with Zn mostly located in the vascular tissues 24 h after the Zn had been applied. Not only do the data presented herein provide new insight for improving the efficiency of foliar Zn fertilizers, but our approach of combining XFM with a transcriptome methodological system provides a novel approach for the study of element translocation in plants. © 2022 Li, Wang, Wu, Blamey, Wang, Chen, Ye, Wang, Paterson, Read, Wang, Lombi, Wang and Kopittke. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.