[Effect of Polyethylene Microplastics on Microbial Necromass Carbon in Different Land Use Type Soils]

Microplastics （MPs） are widely present in terrestrial ecosystems， but the impact of their accumulation on microbial necromass and their contribution to soil organic carbon （SOC） in different land use types is unclear. In this study， 5 mm×5 mm polyethylene microplastics （PE-MPs） sourced from plastic film were added to the grassland， farmland， and facility soil at the dosages of 0% （CK）， 0.03%， and 0.3% （w/w）， respectively， for an eight-week indoor culture experiment. The changes in soil organic carbon and microbial residue carbon were analyzed after the culture was completed. The results showed that： ① The addition of 0.03% and 0.3% PE-MPs reduced the soil MNC content of the three land use types by 5.4%-11.1% and 2.1%-37.1%， respectively， compared with those of CK. Among them， the addition of 0.3% PE-MPs significantly reduced soil MNC content by 19.8% and 37.1% in farmland and facility soils， respectively， and had no significant effect on grassland soil. ② The addition of 0.03% and 0.3% PE-MPs significantly reduced the contribution of soil MNC to SOC by 20.6% and 25.0% in the farmland and by 4.8% and 18.8% in the facility soils， respectively （P<0.05）. The addition of 0.3% PE-MPs increased the contribution of soil MNC to organic carbon in grassland by 5.9%. ③ Soil nitrate nitrogen， dissolved organic nitrogen， and pH were important factors affecting the accumulation of microbial necromass carbon. In conclusion， the accumulation of soil MNC and its contribution to SOC were reduced in both farmland and facility soils after the addition of 0.3% PE-MPs， which was detrimental to soil carbon sequestration.