Rock powder amendment mitigates microplastic induced destabilization of soil organic carbon by modulating molecular composition and microbial assembly

• Rock powder counters microplastic-induced soil organic carbon destabilization. • In microplastic soil, rock powder boosts total soil organic carbon and mineral associated organic carbon. • Rock powder alters microbial assembly, enhancing carbon cycling under microplastic stress. • Rock powder improves dissolved organic carbon thermodynamic stability and molecular traits in microplastic-impacted soils. • Rock powder’s soil organic carbon benefits are mediated by soil physics, microbes and molecular traits. Microplastic contamination poses a significant threat to soil organic carbon (SOC) stability, while enhanced weathering via rock powder application is a promising carbon sequestration technology that enhances SOC through mineral protection. To investigate rock powder’s potential for mitigating microplastic-induced soil degradation, we conducted a controlled soil column experiment with four treatments: control (CK), microplastic (MP), rock powder (RP), and microplastic plus rock powder (MPRP). We analyzed SOC fractions, molecular composition, microbial diversity, carbon-cycling functional genes, and ecological assembly processes. MP treatment substantially decreased mineral-associated organic carbon and altered dissolved organic carbon composition toward higher aromaticity and molecular complexity. RP amendment effectively counteracted these adverse effects, with MPRP treatment showing the highest SOC content and enhanced thermodynamic stability. MP exposure significantly modified microbial community composition and reduced diversity, while RP maintained community structure closer to CK and enhanced carbon-cycling gene abundance. Ecological process analysis revealed that RP increased heterogeneous selection and and homogenizing dispersal processes compared to MP treatment. Structural equation modeling demonstrated that soil physicochemical properties influenced SOC indirectly through microbial communities and organic carbon molecular properties. These findings demonstrate that rock powder amendment effectively mitigates microplastic-induced soil degradation by enhancing SOC content and stability through modulating organic carbon molecular composition, microbial community structure, and ecological assembly processes. This provides a promising nature-based solution for addressing microplastic contamination in soils, though potential environmental and economic trade-offs require further evaluation.