Availability and Shoot Cadmium Content in Wheat Differentially Respond to Liming: The Impact of Exchangeable Calcium and pH in Bulk and Rhizosphere Soil

Cadmium (Cd) contamination in soil poses significant risks to environmental and crop safety. One of the most important parameters controlling Cd uptake by plants from soil is pH. The role of soil pH in regulating Cd availability and its uptake by plants has been studied; however, no study has yet compared how pH changes in the rhizosphere and bulk soil differentially influence these processes. This study examined how nitrification inhibitor (3,4-Dimethylpyrazole phosphate (DMPP)) and lime affect Cd availability and concentration in wheat via modulating pH and calcium (Ca) availability in rhizosphere and bulk soil. Wheat was grown in acidic sandy soil under three lime application rates and two DMPP levels to investigate Cd accumulation. Our results indicated that DMPP application was associated with decreased rhizosphere pH, exchangeable Ca and Cd accumulation in wheat shoots. The impact of lime on shoot Cd varied depending on the presence of DMPP. Liming generally increased soil pH and exchangeable Ca and was associated with decreased plant-available Cd (CaCl₂-extractable Cd) in both bulk soil and the rhizosphere. In the absence of DMPP, liming was associated with a greater increase in exchangeable Ca in the rhizosphere and reduction in plant-available Cd (CaCl₂-extractable Cd) in the rhizosphere and bulk soil. Despite the decline in soil Cd availability, these changes were associated with higher Cd concentration and content in wheat shoots. In contrast, under DMPP application, liming decreased shoot Cd concentration but did not affect shoot Cd content, suggesting that DMPP may influence the response of shoot Cd concentration to liming. The results provide useful insights into Cd management in agricultural systems and may contribute to strategies for reducing Cd-related risks in crop production.