Straw incorporation combined with Cd/As resistant microbial inoculation reduces arsenic and cadmium bioavailability and translocation in Ipomoea aquatica (water spinach)

Straw undergoes a microbial degradation process in soil, influencing heavy metal (HM) speciation through humification and mineralization. This study investigates the combined effect of straw incorporation and Cd/As-resistant microbial inocula on arsenic (As) and cadmium (Cd) co-contaminated soil remediation and their accumulation in water spinach. A pot experiment was conducted to assess changes in soil As/Cd speciation, organic carbon fractions, and water spinach uptake under straw incorporation and microbial inocula, such as the metal-tolerant strains Pseudomonas sp. C and Bacillus sp. D, to assess their impact on phytoremediation efficiency. The results showed that microbial agents C and D significantly increased soil microbial biomass carbon (MBC), while microbial agent C also enhanced soil total organic carbon (TOC) and dissolved organic carbon (DOC) content. Microbial agent D reduced the mobility of As and Cd, shifting As to crystalline iron-aluminum oxide-bound forms and Cd to iron-manganese oxide-bound and organic/sulfide-bound forms. All microbial agents promoted humic acid (HA) accumulation and influenced metal uptake patterns. Microbial agent C enhanced Cd translocation to all plant parts and increased stem As uptake while reducing leaf As content. Microbial agent D reduced As accumulation in roots and leaves but increased stem translocation. These findings suggest that combining straw with microbial inocula improves soil health, reduces HM bioavailability and mobility, offering a sustainable strategy for managing Cd/As co-contaminated agricultural soils. • The effects of straw incorporation and microbial agents on As/Cd-contaminated soil under water spinach cultivation were investigated Straw incorporation combined with microbial agents synergistically boosted water spinach biomass by up to 64.9% in contaminated soil. • Straw incorporation with microbial agent C increased soil TOC by 29.5% and DOC by 90.6%. • Straw incorporation and microbial agents reduce soil As/Cd content and alter HM translocation, reducing leaf As/Cd content.Straw incorporation combined with microbial agent D reduces As and Cd mobility.