Mechanistic insights into mitigating Cd stress in plants using typical organic waste fermentation solutions

Finding practical solutions for utilizing agricultural organic wastes has always been a challenge. To address this, our study investigated the effects and mechanisms of different exogenous organic waste fermentation solutions on alleviating Cd stress in plants using hydroponic experiments. Out of the seven fermentation solutions examined, pea fermentation liquid (T3), chicken manure (T5), molasses (T6), and chitosan oligosaccharide broth (T9) exhibited positive effects. They increased shoot fresh weight by 1.17%, 26.83%, 7.94%, and 15.59%, and root fresh weight by 50.00%, 12.21%, 81.19%, and 19.47%, respectively. Conversely, amino acid mother liquid (T7) and potassium polyaspartate liquid (T8) reduced shoot fresh weight by 34.21% and 24.74%, and root fresh weight by 27.06% and 7.10%, respectively. All organic waste liquids reduced Cd concentration in shoots and roots. Corn fermentation liquid (T4) reduced Cd in shoots from 87.91 to 19.20 mg/kg, while molasses (T6) reduced Cd in roots from 980.94 to 260.47 mg/kg. SEM-EDX results revealed that molasses (T6) effectively repaired Cd damage on root surfaces. In addition, several waste liquids mitigated microelement absorption disturbances. All waste liquids reduced MDA, corn fermentation liquid (T4), chicken manure (T5), molasses (T6), potassium polyaspartate liquid (T8), and chitosan oligosaccharide liquid (T9) significantly decreased H₂O₂ by 21.6-38.3%. Structural equation model (SEM) and correlation analysis highlighted the importance of root Mg, Cu, and Zn content and CAT activity in relieving Cd stress and promoting plant growth. Overall, molasses (T6) and chicken manure (T5) demonstrated the most beneficial combined effects, while amino acid mother liquid (T7) and chitosan oligosaccharide liquid (T9) should be exercised with caution due to their weaker effects.