Effects of iron-modified biochar with S-rich and Si-rich feedstocks on Cd immobilization in the soil-rice system.

Fe-modified biochar has been shown to have high sorption ability for cadmium (Cd), while Cd immobilization effects of Fe-modified biochars with Si-rich and S-rich feedstocks have been rarely addressed. To explore the effects of Fe-modified Si-rich and S-rich biochars on Cd translocation in the soil-rice system, a pot experiment was carried out with an acidic Cd-contaminated sandy loam paddy from central South China and a late season rice cultivate during July to November 2018. Rice straw and rice husk were chosen as Si-rich feedstocks, and rape straw was applied as S-rich feedstock, these feedstocks were further collected and pyrolyzed at 450 °C. Pristine and Fe-impregnated rice straw (BRS/BRS-Fe), rice husk (BRH/BRH-Fe) and rape straw (BRE/BRE-Fe) biochars were applied at 0 and 10 t/ha, respectively. The reductions in Cd concentrations in rice grains were 23.8%, 22.3% and 46.1% with treatments of BRE, BRS and BRH, respectively, compared to the control. Compared to other pristine biochars, BRH is more effective in Cd remediation in paddy soil. For Fe-modified biochars, BRE-Fe achieved the highest reductions in Cd concentrations in rice grains with 46.7% and 30.1%, compared with the control and BRE, respectively. BRE-Fe decreased Cd remobilization from leaves to grains. Only BRE-Fe enhanced the formation and Cd sorption capacity of iron plaque. BRS-Fe and BRH-Fe enhanced Fe content in rice plants, which might induce the reduction in iron plaque formation. Fe and S-contained complexes contents increased in the contaminated pristine biochar particles, but reduced in the contaminated BRE-Fe particles. Therefore, Fe modification could not enhance Cd immobilization effect of Si-rich biochar, while Fe modified S-rich biochar has promising potential for Cd remediation with enhancement in iron plaque formation and Cd fixation in rice leaves.

Potential Implications of Interactions between Fe and S on Cereal Fe Biofortification.

Iron (Fe) and sulfur (S) are two essential elements for plants, whose interrelation is indispensable for numerous physiological processes. In particular, Fe homeostasis in cereal species is profoundly connected to S nutrition because phytosiderophores, which are the metal chelators required for Fe uptake and translocation in cereals, are derived from a S-containing amino acid, methionine. To date, various biotechnological cereal Fe biofortification strategies involving modulation of genes underlying Fe homeostasis have been reported. Meanwhile, the resultant Fe-biofortified crops have been minimally characterized from the perspective of interaction between Fe and S, in spite of the significance of the crosstalk between the two elements in cereals. Here, we intend to highlight the relevance of Fe and S interrelation in cereal Fe homeostasis and illustrate the potential implications it has to offer for future cereal Fe biofortification studies.