New insights into the stages of cadmium remediation in ryegrass enhanced by kitchen compost-derived dissolved organic matter: Activation, absorption, and storage

Dissolved organic matter (DOM) regulates plant behavior in both agricultural and environmental fields. However, the regulatory mechanisms by which DOM influences soil-plant system interactions during the phytoremediation of Cd-contaminated soils remain unclear. Therefore, this study investigated the enhanced effect of kitchen compost-derived DOM on the Cd remediation capability of ryegrass across three phases of phytoremediation. The main pathways and mechanisms of DOM-assisted phytoremediation were identified through the analysis of changes in soil microbial communities and metabolism functions. The results revealed that DOM increased the bioavailability of soil Cd and significantly enhanced the Cd enrichment capacity of ryegrass, regardless of the application rate. The application of 20 % DOM to soil with a 20 mg/kg Cd content increased the bioconcentration factors of ryegrass roots and shoots by up to 38.19 and 11.08 times, respectively, compared with the control group. The direct or indirect optimizing effects of DOM on Cd fraction transformation, microbial communities, and their metabolism functions significantly enhanced the Cd enrichment capacity of ryegrass. Notably, DOM exhibited dual effects on ryegrass growth, mainly influenced by changes in soil physicochemical properties, optimization of microbial communities, and alterations in nitrogen metabolic functions. Additionally, the Cd reserves in ryegrass, which serve as a vital indicator of phytoremediation, exhibited a positive response to DOM. This study provides insights into the various reinforcing roles of kitchen compost-derived DOM in Cd-contaminated soil phytoremediation. These findings support the development of effective agronomic strategies for precise Cd regulation.