Marigold can protect crops against soil-borne diseases. However, the effects of intercropping with marigold on apple rhizosphere soils are not known. In this study, we investigated the metabolite profiles and bacterial community structures in rhizosphere soils of the apple-marigold intercropping system by high-throughput sequencing and soil metabolomics. The results show that intercropping marigold could significantly enhance soil moisture, nitrogen, and enzyme activities compared with clean tillage. The soil metabolite profiles and the soil bacterial community structures in the rhizosphere soils were different between the inter-and mono-cropping systems. Among nine metabolites, carbohydrates were more increased in the intercropping system than in the monocropping system. Pathway enrichment analysis revealed that the greatest differential, in terms of metabolic pathway, was starch and sucrose metabolism. Moreover, intercropping marigold significantly increased the relative abundance of plant growth promoting bacteria in rhizosphere soils, such as Rhizobiales, Pseudomonadales, and Bacillales. These results indicate that marigold intercropping positively affected the apple orchard’s soil quality and may provide a new intercropping technique to improve soil fertility in orchards and promote plant growth.

Cadmium(Cd)contamination poses significant risks to agricultural productivity and ecosystems, necessitating effective remediation strategies. This study evaluated the efficacy of iron (Fe)-modified corn straw biochar (FB) in immobilizing Cd and reducing its uptake in lettuce, compared to raw biochar (B). FB was synthesized by pyrolyzing Fe(NO₃)₃-treated corn straw and characterized for physicochemical properties. Pot experiments tested Cd immobilization at 0, 1, and 2 mg kg⁻¹ Cd levels with 0%, 1%, and 3% (w/w) B or FB applications. Results demonstrated that FB exhibited higher specific surface area, pore volume, and oxygen-containing functional groups than B, enhancing Cd adsorption via mechanisms including surface complexation (-OH, Fe-O), precipitation (CdCO₃), and π-π interactions. FB reduced soil bioavailable Cd by 15–28% and shifted Cd speciation from exchangeable to Fe/Mn oxide-bound fractions, outperforming B even at lower doses (1% FB ≈ 3% B). Additionally, FB improved soil fertility, enzyme activities, and enriched Cd-immobilizing bacteria , promoting lettuce growth and reducing Cd content in roots (25–40%) and leaves (33–47%). The findings highlight FB as a cost-effective and sustainable amendment for Cd-contaminated soils, combining enhanced adsorption, microbial modulation, and reduced application rates. This study provides critical insights into Fe-modified biochar’s dual role in soil remediation and crop safety, supporting its practical application in sustainable agriculture.