High temperatures and microplastic enhanced inorganic phosphorus mineralization and phoD-harboring bacterial abundance in paddy soil

Microplastic (MP) pollution in agricultural soils poses a significant threat, particularly under changing climatic conditions. This study investigates the combined effects of MP contamination and elevated temperatures (29°C and 42°C) on paddy soil nutrient dynamics, rice physiology in heat-sensitive and heat-tolerant genotypes, rhizosphere phoD-harboring bacteria, and microbial community composition in a controlled growth chamber. Soil properties, gene expression, and microbial diversity were analyzed using flow injection analysis, qPCR, and high-throughput sequencing. At 29°C, MP exposure reduced soil inorganic phosphorus (Pi), dissolved organic carbon (DOC), dissolved organic nitrogen (DON), and NO₃⁻-N by 7-50 %, while increasing NH₄⁺-N by 21-26 %, with greater effects on heat-sensitive genotypes. Conversely, at 42°C, MP increased Pi, DOC, DON, and NO₃⁻-N by 5-35 % and decreased NH₄⁺-N by 16-28 %. MP reduced phoD and 16S rRNA gene abundance at 29°C (0.74-0.96-fold) but increased them at 42°C (0.28-9.31-fold). Rice phosphorus transporter gene expression varied, with OsPT1 and OsPT6 upregulated at 29°C and OsPT8 at 42°C. Microbial diversity increased at 42°C, favoring Proteobacteria, Actinobacteria, and Burkholderiaceae, while Firmicutes and Acidobacteria declined, especially in heat-sensitive rice. Key taxa like Geobacter, Clostridium, and Zopfiella were enriched at 42°C, improving Pi availability and plant biomass. Enhanced amino acid and carbohydrate metabolism at 42°C supported rice growth despite MP contamination. This study reveals how rising temperatures modulate microplastic impacts on soil nutrient cycling and microbial activity, highlighting critical interactions for sustainable agriculture under climate change.