Abscisic acid-producing bacterium Azospirillum brasilense effectively reduces heavy metals (cadmium, nickel, lead, and zinc) accumulation in pak choi across various soil types

Heavy metal contamination of soil is a serious environmental issue that threatens agricultural products and human health. Previous studies have shown that abscisic acid (ABA)-producing bacteria can effectively decrease heavy metal accumulation in plants. However, the broader applicability of this approach across varying soil types remains undetermined, revealing significant gaps in understanding its real-world implementation under distinct edaphic conditions. Garden soils were collected from Zhejiang, Sichuan, and Heilongjiang Provinces to investigate the effects of ABA-producing bacteria in reducing heavy metal accumulation in vegetable crops grown in moderately contaminated soils in this study. Inoculating the ABA-producing bacterium Azospirillum brasilense decreased heavy metals contents, including cadmium (Cd), nickel (Ni), lead (Pb), and zinc (Zn) in pak choi grown in the soil from Zhejiang, Heilongjiang, and Sichuan Provinces by 30.2-52.4 %, 24.1-30.1 %, and 22.0-49.2 %, respectively. Additionally, pak choi biomass increased significantly by 134.3 %, 87.9 %, and 126.3 % in these soils, respectively. These results indicated that ABA-producing bacteria universally benefited from heavy metal reduction and yield improvement. Further analysis revealed that the ABA levels in plants increased by 24.7 %, 27.7 %, and 11.9 %, IRT1 expression decreased by 34.9 %, 8.6 %, and 30.8 %, and IRT2 expression decreased by 34.2 %, 20.1 %, and 9.2 % in those soils, respectively. Structural equation modeling analysis confirmed that increased soil pH and decreased available heavy metals contributed to the reduced heavy metal accumulation in pak choi. Overall, the ABA-producing bacteria effectively reduced heavy metal accumulation and enhanced biomass across different soil types, with the most pronounced effect observed in the soil of Zhejiang. Consequently, the application of ABA-generating bacteria may be an alternative strategy for improving the biomass production and quality of vegetable plants grown in heavy metal-contaminated soils.