Germanium fractions in typical paddy soil and its interaction with humic substances
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RESEARCH ARTICLE
Germanium fractions in typical paddy soil and its interaction with humic substances Bolun Fan 1 & Molan Tang 1 & Lingyang Yao 2 & Aobo Zhang 3 & Hanqin Yin 3 & Weilin Yang 1 & Zhenzhen Ma 1 & Wu Xiang 4 & Zhengyu Bao 1,2,5 Received: 18 July 2020 / Accepted: 29 October 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract Ge and Si differ strongly in their biogeochemical behavior due to the differences in binding capacity to organic matter. The mechanisms of soil organic matter affecting the mobility and bioavailability of Ge in soil-plant system remain unclear. This work aimed to investigate the soil Ge fractions and Ge binding to humic substances in paddy soil. Paddy soil samples taken from Changxing County, Zhejiang Province, China, were investigated by the sequential extraction method. Humic acid (HA) and fulvic acid (FA) isolated from paddy soils were characterized by Fourier transform infrared spectrometry (FT-IR) and 3-dimensional excitation-emission matrix (3D-EEM). The effect of humic substances on the binding of Ge was studied by fluorescence-quenching titration. Results showed that residual Ge was the dominant fraction in soil (up to 85%). The mobile Ge, organic matter bound Ge and easily reduceable compounds bound Ge accounted for approximately 10% of soil TGe and may represented critical labile pools of soil Ge. Organic matter bound Ge significantly correlated (r = 0.56, p < 0.01) with rice Ge concentrations. The fluorescence of HA and FA was markedly quenched by the addition of Ge. The conditional stability constant of HA-Ge complexes was larger than that of FA-Ge complexes, and the complexation capacity of HA-Ge complexes was lower than that of FA-Ge complexes. Humic substances played a dual role in affecting the behavior of dissolved Ge in paddy soil. HA formed stable complexes with Ge and tended to sequester Ge, while FA formed soluble and unstable complexes with Ge and tended to act as a Ge carrier in soil-plant system. Keywords Germanium . Soil germanium fractions . Organic matter-bound germanium . Humic substances . Complexation . Stability constants Highlights (1) Approximately 10% of total soil germanium exists in labile pools that is potentially available for plants. (2) Organic matter-bound Ge may increase the transfer of Ge from soil to plants. (3) In soil-plant system, humic acids sequester Ge, while fulvic acids act as carrier of Ge. Responsible editor: Kitae Baek * Zhengyu Bao [email protected] 1
Faculty of Materials Science and Chemistry, China University of Geosciences, Wuhan 430074, Hubei, China
2
Zhejiang Institute, China University of Geosciences, Zhejiang 311305, Hangzhou, China
3
Zhejiang Institute of Geological Survey, Zhejiang 311203, Hangzhou, China
4
School of Earth Sciences, China University of Geosciences, Wuhan 430074, Hubei, China
5
Ankang Se-Resources Hi-Tech Co., Ltd, Ankang 725000, Shaanxi, China
Introduction As a rare metal, Ge is classified as a technology-critical element (TCE) (Wojcieszek et al. 2017) and is widely dis
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