Effects of microplastics on soil carbon pool and terrestrial plant performance

Abstract Soil, as a primary repository of plastic debris, faces an escalating influx of microplastics. Microplastics have the potential to decrease soil bulk density and pH, as well as alter soil pore structure and aggregation. These changes in soil physicochemical properties subsequently lead to habitat degradation for microbes and environmental shifts that impact plant growth. Masquerading as soil carbon storage, microplastics can distort assessments of the soil carbon pool by introducing plastic-carbon and associated leachates, influencing soil organic matter (SOM) turnover through priming effects (e.g., dilution, substrate switching, and co-metabolisms). Additionally, microplastics can influence the distribution of soil carbon in particulate and mineral-associated organic matter, consequently affecting the accumulation and stability of soil carbon. Furthermore, microplastics can also influence the chemodiversity of dissolved organic matter (DOM) in soils by increasing DOM aromaticity and molecular weight while deepening its humification degree. The changes observed in soil DOM may be attributed to inputs from microplastic-derived DOM along with organo-organic and organo-mineral interactions coupled with microbial degradation processes. Acting as an inert source of carbon, microplastics create a distinct ecological niche for microbial growth and contribute to necromass formation pathways. Conventional microplastics can reduce microbial necromass carbon contribution to the stable pool of soil carbon, whereas bio-microplastics tend to increase it. Furthermore, microplastics exert a wide range of effects on plant performance through both internal and external factors, influencing seed germination, vegetative and reproductive growth, as well as inducing ecotoxicity and genotoxicity. These impacts may arise from alterations in the growth environment or the uptake of microplastics by plants. Future research should aim to elucidate the impact of microplastics on microbial necromass accumulation and carbon storage within mineral-associated fractions, while also paying closer attention to rhizosphere dynamics such as the microbial stabilization and mineral protection for rhizodeposits within soils. Graphical Abstract