[Effects of Microplastics and their Properties on Soil Organic Carbon Fractions: A Meta-analysis]

The potential effects of microplastics （MPs） on soil organic carbon （SOC） and its components have attracted much attention in recent years. However， existing research tends to focus on the study of the effect of a single MPs characteristic on a single SOC component， and it is difficult to reveal the mechanism of the effect of multiple MPs characteristics on the inter-transformation among SOC components. Therefore， in this study， the Meta-analysis method was used to integrate and analyze 846 case data from 51 publications published between 2017 and May 2025， and the effects of MPs characteristics （type， mass fraction， and particle size） on SOCs and their fractions were systematically evaluated using the R language random-effects model and the mixed-effects model. The results showed that the addition of MPs significantly increased the content of soil organic carbon （SOC）， dissolved organic carbon （DOC）， microbial biomass carbon （MBC）， and mineral-bound organic carbon （MAOC） fractions by 25.14%， 30.42%， 31.90%， and 62.50%， respectively， while no significant effect was observed on the content of particulate organic carbon （POC） and permanganate-oxidizable organic carbon （POXC）. The increase in MAOC content reflected the potential contribution of MPs to the long-term retention and stability of SOC. The mass fraction of MPs was significantly positively correlated with its effect size on SOC， DOC， MBC， and MAOC concentrations， but significantly negatively correlated with its effect size on POXC， whereas the particle size of MPs was significantly negatively correlated with its effect size on SOC， DOC， and POXC， and positively correlated with its effect size on MAOC. Between-group differences in the effects of MPs on the content of stable organic carbon fractions （MAOC） versus reactive organic carbon fractions （POC and POXC） suggest that MPs may facilitate the conversion of reactive organic carbon fractions to stable organic carbon fractions. This study analyzed the characteristics of the changes in soil organic carbon content after the addition of MPs from the perspective of the mutual transformation of soil organic carbon components， which helps to explore the complex mechanism of the influence of MPs on the soil carbon cycle process.