Plastic Film Residue Reshaped Protist Communities and Induced Soil Nutrient Deficiency Under Field Conditions

The use of plastic agricultural mulching films presents a “double-edged sword”: while these films enhance crop yields, they also lead to the accumulation of plastic film residues in the soil, creating new pollutants (microplastics). Our understanding of the “plastisphere”, a niche formed by agricultural film residues in the soil, where unique microbial communities and soil conditions converge remains limited. This is particularly true for protists, which are recognized as key determinants of soil health. Therefore, this study simulated a field experiment to analyze the effects of long-term plastic film residues on the structure of protist microbial communities in the rhizosphere, bulk soil and plastisphere of oilseed rape as well as their effects on soil nutrients. The results revealed that the residual plastic films underwent significant structural and chemical degradations. Protist diversity and co-occurrence network complexity were markedly reduced in plastisphere soils. In addition, soil moisture content, inorganic nitrogen and available phosphorus levels declined, leading to deficiencies in soil nutrients. Functional shifts in consumer protists and phototrophs along with weakened network interactions, have been identified as key drivers of impaired nutrient turnover. Our study underscores the critical role of protist communities in maintaining soil nutrient cycling and highlights the profound adverse effects of plastic film residues on soil ecosystems. These findings provide valuable insights into mitigating plastic residue accumulation to preserve long-term soil fertility and ensure sustainable agricultural productivity.