Rice Rhizospheric Effects on the Bioavailability of Toxic Trace Elements during Land Application of Biochar

Wen Fang, Yi Yang, Hailong Wang, Danxing Yang, Jun Luo, Paul N. Williams*

*Corresponding author for this work

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Land application of biochar, the product of organic waste
carbonization, can improve soil fertility as well as sequester carbon to
mitigate climate change. In addition, biochar can greatly influence the
bioavailability of toxic trace elements (TTEs) in soils resulting from its large
internal surface areas, abundance in organic carbon, and ability to modify
soil pH. Most research to date employs batch leaching tests to predict how
biochar addition impacts TTE bioavailability, but these ex situ tests rarely
considered the rhizospheric effect which might offset or intensify the
changes induced by organic residue addition. This is especially so in rice
rhizospheres because of strong clines in localized redox conditions. In this
study, we adopted in situ high-resolution (HR) diffusive gradients in thin
films (DGT) as well as rhizo-bag porewater sampling experiments to depict
an overall picture of the difference in TTE (As, Cd, Cu, Ni, and Pb)
bioavailability between the rice rhizosphere and bulk soils during land
application of biochar. Porewater sampling experiments revealed that biochar additions stimulated TTE release due to the increase of dissolved organic carbon (DOC) and H+ concentrations. In the rhizosphere, although biochar still promoted As, Cd, and Ni release into porewaters, the rhizospheric effect was one of dampening/reduction compared with the bulk soil. When we focused on the localized changes of TTE bioavailability in the rhizosphere using an in situ HR-DGT approach, on the contrary, flux maxima of Cd, Cu, and Ni occurred near/on the root surface, and hot spots of As can be observed at peripheries of the rooting zone, which demonstrated the high heterogeneity and complexity of the rhizosphere’s influence on TTE bioavailability.
Original languageEnglish
JournalEnvironmental Science and Technology
Early online date17 Mar 2021
Publication statusEarly online date - 17 Mar 2021


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