Thiol-modified rice straw biochar (RS) was prepared by an esterification reaction with βmercaptoethanol and used for the remediation of Cd and Pb polluted soils. Modified biochar was characterized through elemental analysis, BET analysis, FE-SEM, FT-IR and XPS. These analyticalcharacterizations confirmed that the thiol groups were successfully grafted onto the surface of the biochar and were involved in the metal ion complexation. The batch sorption experiments showed that Cd 2+ and Pb 2+ sorption onto RS followed a pseudo second order kinetic model and a Langmuir isotherm. The maximum adsorption capacities for Cd 2+ and Pb 2+ were 45.1 and 61.4 mg g -1 , respectively in the single-metal systems. In contrast, Cd 2+ was selectively adsorbed over Pb 2+ by RS in the binary-metal systems. Both Cd 2+ and Pb 2+ were mainly removed through surface complexation. The soil incubation experiments further showed that RS reduced the available Cd concentrations up to 40% while available Pb concentrations was reduced up to 11%. Overall, this study demonstrates thiol-modified biochar can effectively enhance the remediation of heavy metal polluted soils.

Cadmium (Cd) is a heavy metal and is highly toxic to all plant species. However, the underlying molecular mechanism controlling the effects of auxin on the Cd stress response in maize is largely unknown. In this study, the transcriptome produced by maize ‘Zheng 58’ root responses to Cd stress was sequenced using Illumina sequencing technology. In our study, six RNA-seq libraries yielded a total of 244 million clean short reads and 30.37 Gb of sequence data. A total of 6342 differentially expressed genes (DEGs) were grouped into 908 Gene Ontology (GO) categories and 198 Kyoto Encyclopedia of Genes and Genomes terms. GO term enrichment analysis indicated that various auxin signaling pathway-related GO terms were significantly enriched in DEGs. Comparison of the transcript abundances for auxin biosynthesis, transport, and downstream response genes revealed a universal expression response under Cd treatment. Furthermore, our data showed that free indole-3-acetic acid (IAA) levels were significantly reduced; but IAA oxidase activity was up-regulated after Cd treatment in maize roots. The analysis of Cd activity in maize roots under different Cd and auxin conditions confirmed that auxin affected Cd accumulation in maize seedlings. These results will improve our understanding of the complex molecular mechanisms underlying the response to Cd stress in maize roots.

Much research has considered the influence of biochars on the availability and phytoaccumulation of potentially toxic elements (PTEs) from soil. However, the vast majority of these studies use, what are arguably, unrealistic and unpractical amounts of biochar (10, 50 and even up to 100 t/ha