Soil revitalization: Montmorillonite's role in mitigating cadmium toxicity and improving wheat growth under water...

Montmorillonite clays effectively adsorb cadmium (Cd) from polluted soils; however, their mechanisms and effects on microbial diversity, soil quality, and wheat phytotoxicity, especially in contaminated and water-stressed environments, remain inadequately explored. This study evaluated raw montmorillonite amendments (RMA), acid-modified montmorillonite amendments (AMA), and magnesium-modified montmorillonite amendments (MMA) under three water regimes: severe deficit irrigation (DI₅₀), moderate deficit irrigation (DI₇₀), and mild deficit irrigation (DI₉₀). Results showed that DI₉₀ × MMA increased soil pH and water-soluble organic carbon, achieving a Cd removal efficiency of 41.8 % compared to DI₅₀ × RMA. Also, DI₉₀ × MMA reduced Cd extractability in soil, converting it from the acid-soluble to the residual fraction. Microbial analysis indicated that MMA reduced Proteobacteria and Actinobacteria while increasing Bacteroides under DI₉₀ conditions, enhancing α-diversity and soil health. In comparison to DI₅₀ × AMA, the DI₉₀ × MMA treatment reduced Cd uptake by plants, leading to an increase in root surface area and a decrease in H₂O₂ levels in roots. Furthermore, leaf glutamine synthetase (319 μmol/(g.h)) and catalase (29.3 μg/min) were higher in DI₉₀ × MMA compared to DI₅₀ × RMA (85.5 μgmol/(g.h)) and (11.1 μmol/(g.h)), respectively. Reducing Cd content in plant tissues improved the plant cell ultrastructure and cell cycle progression by decreasing the malonaldehyde (12.9 μmol/g) level, mitigating Cd phytotoxicity and promoting wheat growth. This strategy offers an alternative to chemical extractants for Cd removal using clay adsorbents, although careful optimization of montmorillonite addition is necessary to avoid adverse impacts on soil texture, root development and overall soil health.