In Vivo Evaluation of Zn Foliar Uptake and Transport in Soybean Using X-ray Absorption and Fluorescence Spectroscopy

Abstract

Understanding the mechanisms of absorption and transport of foliar nutrition is a key step towards the development of advanced fertilization methods. This study employed X-ray fluorescence (XRF) and X-ray absorption near edge spectroscopy (XANES) to trace the in vivo absorption and transport of ZnO and ZnSO₄(aq) to soybean leaves (<i>Glycine max</i>). XRF maps monitored over 48 h showed a shape change of the dried ZnSO₄(aq) droplet, indicating Zn²⁺ absorption. Conversely, these maps did not show short movement of Zn from ZnO. XRF measurements on petioles of leaves that received Zn²⁺ treatments clarified that the Zn absorption and transport in the form of ZnSO₄(aq) was faster that of ZnO. Solubility was the major factor driving ZnSO₄(aq) absorption. XANES speciation showed that in planta Zn is transported coordinated with organic acids. Because plants demand Zn during their entire lifecycle, the utilization of sources with different solubilities can increase Zn use efficiency.