Fe-Ca layered double hydroxide corn straw biochar alleviates heavy metal oxidative stress in Bidens pilosa L.: Rhizosphere effects

Fe-Ca LDH biochar (Fe-Ca LDH-CSB) was prepared by coprecipitation using corn stover as the raw material. Fe-Ca LDH-CSB was applied to the rhizosphere soil of Bidens pilosa L. (B. pilosa L.) to explore the effects of Fe-Ca LDH-CSB on the rhizosphere soil environment and how it helps B. pilosa L. cope with oxidative stress caused by heavy metals (HMs) (Cd, Pb, Zn, and Cu) in the environment. Pot experiments were conducted in low-HM-contaminated (LC) soil and high-HM-contaminated (HC) soil with four Fe-Ca LDH-CSB addition levels. The results showed that the addition of Fe-Ca LDH-CSB increased the rhizosphere soil pH and reduced the acid-soluble forms of HMs, by 19.1 %-44.1 % in HM-contaminated soil at the maximum addition. Specifically, in the LC soil, dehydrogenase activity increased with the addition of Fe-Ca LDH-CSB. The addition of Fe-Ca LDH-CSB also increased the activities of amylase, invertase, urease, and alkaline phosphatase in the soil, promoting an increase in the soil nutrient content. In the LC soil, Fe-Ca LDH-CSB addition significantly affected the relative abundances of Bacillus, Pseudarthrobacter and Neocosmospora, while in the HC soil, the relative abundances of Bacillus, Alternaria and Articulospora were affected. The increased abundance of these microbes contributed to enhanced plant biomass. Fe-Ca LDH-CSB addition helped to increase the biomass of B. pilosa L. and reduce the HM concentration in B. pilosa L. Additionally, the addition of Fe-Ca LDH-CSB reduced the levels of reactive oxygen species (ROS) in B. pilosa L. Peroxidase (POD) and glutathione (GSH) were crucial in reducing the oxidative stress induced by HMs in B. pilosa L. These findings highlight that Fe-Ca LDH-CSB simultaneously improves soil health and plant resilience against HMs, offering dual benefits for promoting environmental sustainability and providing a promising approach for soil remediation and plant protection in contaminated environments.