Soil cadmium pollution decreases phosphorus-mineralizing microbial diversity and reduces phosphorus availability

Cadmium (Cd) has become a major environmental concern, adversely affecting soil quality and crop productivity. Cd pollution disrupts soil nutrient cycling, particularly phosphorus (P), which is crucial for plant growth. In this study, we conducted a meta-analysis to assess the impact of Cd on soil phosphorus availability, followed by pot experiments using maize (Zea mays) to investigate the effects of varying Cd concentrations (0, 0.5, 1.0, 2.5, and 5.0 mg/kg) on phosphorus uptake, soil phosphorus fractions, and microbial diversity. The results revealed that when soil Cd concentrations exceeded 1.0 mg/kg, maize growth and phosphorus uptake were significantly inhibited (P < 0.05), with a 25.3-64.9% reduction in yield. Cd pollution decreased soil available phosphorus and altered its chemical forms, as indicated by a decrease in soluble P fractions (H₂O-Pi, NaHCO₃-Pi) and an increase in insoluble P fractions (NaOH-Pi, HCl-Pi). Total organic and inorganic phosphorus increased by 5.6-29.4% and 5.8-23.5%, respectively, while active phosphorus decreased by 19.3-58.6%, and steady-state phosphorus increased by 5.2-26.0%. The activities of alkaline phosphatase (AKP) and acid phosphatase (ACP) were significantly reduced under higher Cd concentrations (P < 0.05). Microbial biomass carbon (MBC) decreased significantly, while phosphorus transformation-related genes (phoD, phnK, ppx, pqqC) were reduced by up to 82.4%. In summary, Cd pollution significantly alters maize rhizosphere microbial communities, reduces the abundance of phosphorus transformation-related microorganisms and functional genes, and disputes phosphorus mineralization. These changes reduced soil active phosphorus content, ultimately decreasing phosphorus availability for maize. This study emphasizes the need for further research on Cd-induced phosphorus transformation mechanisms and microbial responses, and suggests developing soil management strategies to mitigate the adverse effects of Cd on phosphorus availability.