Plant–Soil–Microbial Regulation Mediated by Mercapto-Modified Nanosilica Mitigates Cadmium Accumulation in Pak Choi ( <i>Brassica chinensis</i> L.)

Effective and sustainable strategies to reduce cadmium (Cd) accumulation in leafy vegetables grown on alkaline soils remain limited. Here, mercapto-modified nanosilica (MS) was developed and evaluated for mitigating Cd uptake in pak choi. MS3 exhibited an 11-fold higher Cd adsorption capacity than unmodified nanosilica, attributed to strong chemisorption via mercapto groups. Soil incorporation (0.1% w / w ), irrigation (800 mg·L –1 ), and foliar spraying (100 mg·L –1 ) of MS3 significantly reduced Cd concentrations in edible tissues by 59.9%, 64.7%, and 43.8%, respectively, while increasing leaf biomass by 24.5%–38.1%. Soil- and irrigation-applied MS3 decreased bioavailable Cd and enriched beneficial bacteria ( Lysobacter, Sphingomonas ). Transcriptomic analysis revealed that MS3 enhanced Cd detoxification by upregulating photosynthesis and cell wall synthesis genes and modulating transporters (downregulating HIPP and COPT to inhibit Cd uptake, while upregulating HMA5, ABCG40, and MTP to promote vacuolar sequestration). These findings highlight MS3 as a promising nanotechnology for ensuring crop safety in Cd-contaminated alkaline soils.