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

Abstract

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.

Long-term biochar application influences phosphorus and associated iron and sulfur transformations in the rhizosphere

“…4a and b). In contrast to previous findings (Fang et al 2021b;Yin et al 2020;Williams et al 2014), no apical Fe flux hotspots were observed in our study (Fig. 3).…”

Study on the soil microbial community structure of the Rhizosphere of Camellia sinensis L. in Anping Village, Kaiyang County, Guizhou Province

“…Many scholars have carried out in-depth studies of rhizospheric microflora in model plants and crops such as Arabidopsis thaliana (Bressan et al 2009), corn (Jin et al 2013), and rice (Fang et al 2021) and found that substances secreted by plants can drive and shape different rhizospheric microbial processes. In other words, rhizosphere microorganisms mainly attract specific microbial populations through rhizosphere exudates.…”

Distinct response of arsenic speciation and bioavailability to different exogenous organic matter in paddy soil

“…It has been widely reported that DOC is an important factor controlling the soil As release and dissolved organic matter will favor the As mobilization through the J o u r n a l P r e -p r o o f formation of dissolved As-Fe-NOM collids/complexes and the reduction of As V to As III under the strongly reducing condition stimulated by exogenous organic matter (Fang et al, 2021). Also, the dissolved organic matter will compete with As for adsorption sites on soil reactive surfaces.…”