Peng Xu, Lei Li, Yunmei Wei, Yun Xu, Yuhang Zhang, Wenjie Ye, Xuya Peng
This study integrated a two-stage immobilization-cultivation experiment to evaluate the effects of three immobilization strategies (inorganic, organic, and organo-mineral amendments) and two fertilization modes (mineral fertilizer alone and partial substitution with organic fertilizer) on soil cadmium (Cd) immobilization and plant Cd accumulation. During the immobilization phase, the organo-mineral strategy achieved the highest Cd immobilization efficiency of 69.5%. In the cultivation phase, the use of mineral fertilizer alone led to Cd remobilization, whereas organic substitution maintained or even enhanced immobilization, reducing shoot Cd accumulation in pak choi by up to 58.3%. Notably, the combined organic immobilization and organic substitution treatment (OP) was particularly effective: despite not having the lowest soil available Cd, it achieved the lowest plant Cd accumulation (2.83 mg·kg-1). Genomic analysis indicated that the OP treatment enriched core metagenome-assembled genomes (MAGs), including MAG8/Pelagerythrobacter, MAG13/Sphingomicrobium, and MAG30/VAYN01, which contained the highest abundances of genes related to extracellular polymeric substance (EPS) synthesis, phosphorus mobilization, and complexation-precipitation, suggesting the potential of these microbes to enhance EPS secretion and phosphate precipitation for rhizospheric Cd interception. This functional potential, along with the measured high EPS content (259.88 mg·kg-1) and low plant Cd accumulation in the OP group, provides coherent correlative evidence supporting the hypothesis that an "EPS barrier-chemical precipitation" mechanism synergistically reduces Cd migration to root surfaces. Collectively, continuous organic management can maintain soil fertility, enhance Cd immobilization, and promote low-Cd crop production, offering an efficient strategy for the safe utilization of remediated farmland.