Mechanism of nanoplastics altering soil carbon turnover under freeze-thaw cycle

Nanoplastics (NPs) affect soil carbon (C) turnover, but their influence on this process through modifications in soil aggregate stability under freeze-thaw cycles remains unclear. In this study rare earth oxides (REOs) and C isotope (¹³C) labeling, combined with Soil Microstructure Scanning Computed Tomography (SMS-CT) and data modeling, were used to examine the relationship between soil aggregate turnover and C turnover under NPs. Compared with the control group, the total phase porosity and surface area of soil treated with NPs increased by 11.9 % and 30.9 %, respectively under freeze-thaw cycle. NPs exhibited a positive effect on the stability of soil aggregates, and the change in soil aggregate stability were attributed to shifts in aggregate composition. During the freeze-thaw cycle, the distribution of ¹³C in 0.5-1 mm aggregates decreased by 41.9 % compared with the control group, while it increased by 60.8 % in < 0.25 mm aggregates, indicating NPs redirected C toward microaggregates. Freeze-thaw cycles improved the connection between soil aggregates and C turnover, whereas NPs increased resistance of aggregate to freeze-thaw forces. This study provides new insights into the environmental effects of NPs on soil ecosystems and food security.