Microplastic-Derived Dissolved Organic Matter Regulates Soil Carbon Respiration via Microbial Ecophysiological Controls

Microbial regulation of soil carbon sequestration is vulnerable to anthropogenic stressors, notably microplastic pollution. Microplastics can release carbon-based compounds that serve as potential substrates for soil heterotrophic microbes. The impact of this novel microplastic-derived dissolved organic matter (MP-DOM) on soil carbon cycling and the underlying mechanisms remain largely unexplored. Here, short-term soil microcosm experiments were conducted with MP-DOM sourced from pristine and aged microplastics to compare their effects on soil carbon respiration against natural dissolved organic matter (NOM). The underlying mechanisms are investigated by estimating the spectroscopic and molecular signatures of MP-DOM and NOM, and comparing their effects on soil microbial physiological properties. Our findings reveal that MP-DOM leads to 36.9-42.3% higher CO2 emissions from soils than NOM, attributed to its greater bioavailability. MP-DOM simultaneously stimulates greater microbial quantity, phenotypic activities, and carbon utilization efficiency because this carbon is more biochemically accessible than NOM. Network analysis indicates stronger interconnections among labile molecules and bacterial taxa in MP-DOM treatments compared to NOM-treated soils, suggesting enhanced microbial capacity to utilize the more readily available MP-DOM. This study demonstrates that MP-DOM accelerates soil microbial respiration by mediating their physiological traits, with potential implications for climate change.