Liming offers unique benefits for reducing cadmium (Cd) uptake in crops by lowering soil Cd bioavailability. However, its effectiveness in reducing Cd accumulation in wheat grains is often insufficient, and the underlying mechanisms remain unclear. This study employed rhizobag pot experiments to systematically evaluate the self-limiting factors of liming on Cd uptake in wheat, focusing on micronutrient dynamics, rhizosphere organic acid secretion, and Cd transporter gene expression. Lime addition (0.5–4.0 g·kg −1 ) significantly increased soil pH and reduced Cd availability by up to 95.4%, but Cd accumulation in wheat grains decreased only 27.9% maximally at 2.0 g·kg −1 . Higher dosages (4.0 g·kg −1 ) failed to further reduce grain Cd concentrations and significantly inhibited plant growth. Liming markedly decreased Fe, Mn, and Zn availability in rhizosphere soil while stimulating rhizosphere secretion of low-molecular-weight organic acids (LMWOAs; e.g., malic, citric, and quinic acids). Exogenous organic acid application experiments confirmed that enhanced LMWOA secretion may subsequently increase rhizosphere Cd availability, promoting Cd uptake in plants. Furthermore, liming upregulated root Cd transporter gene expression ( TaIRT1, TaZIP3, TaZIP5, TaNRAMP3, and TaHMA2 ), possibly facilitating Cd uptake. These combined mechanisms—decreased soil micronutrient availability, enhanced LMWOAs in the rhizosphere, and increased expression of Cd transporter genes—compromised lime's efficacy in mitigating wheat Cd uptake. This study contributed to optimizing soil-wheat system remediation strategies.
Tong et al. (Sat,) studied this question.