Mercapto-Functionalized Carbon Dots Reduce Cadmium Accumulation in Wheat Grains via Plant–Soil–Microbial Regulation
Li Zhang, Lijie Zhao, Ajit K. Sarmah, Jian Sun, Nan Zhao, Qiang Zeng, Yuepeng La, Dasong Lin, Ruigang Wang
Abstract
Sustainable strategies to reduce Cd accumulation in wheat grown on Cd-contaminated alkaline soils remain limited. Here, we developed mercapto-functionalized carbon dots (SH-CDs) from Salvia miltiorrhiza biomass via a solvent-free ball milling approach with 3-mercaptopropyltrimethoxysilane. SH-CDs exhibited superior Cd 2+ adsorption capacity (35.9 mg·g –1 ), primarily attributed to the strong affinity of surface-bound mercapto (−SH) groups, as confirmed by DFT calculations. SH-CDs applied via soil irrigation (800 mg·L –1 ) and foliar spraying (1 mg·mL –1 ) effectively reduced Cd content in wheat grains by 61.1% and 43.8%, respectively, compared to the control group (CK), while grain yield increased significantly by 24.5% and 12.4%. Soil irrigation with SH-CDs transformed soil Cd into less bioavailable fractions, reducing diethylenetriaminepentaacetic acid-extractable Cd (DTPA-Cd) by 13.6–45.7%. Integrated transcriptomic and metabolomic analyses revealed that SH-CDs mitigate Cd accumulation and phytotoxicity through: (1) enhancing photosynthesis (upregulating Lhca/b, Psa, Psb genes) and antioxidant defense (elevating SOD, CAT, POD, GSH; upregulating GST, APX); (2) promoting Cd sequestration in cell walls via remodeling genes involved in lignin, cellulose, and pectin biosynthesis; (3) regulating Cd transporters (upregulating ABCG3/7, ABCC2/3/4; downregulating HIPP27/45); and (4) reprogramming stress-related metabolites (amino acids, lipids, flavonoids). Additionally, SH-CDs irrigation enriched soil plant-growth-promoting and heavy-metal-resistant bacteria (e.g., Lysobacter and Vicinamibacteraceae ). This work elucidates the multifaceted plant–soil–microbe mechanisms underpinning the efficacy of SH-CDs, demonstrating their potential as a nanoenabled strategy for safe crop production in Cd-contaminated farmlands.