The effects of long-term residues of poly(butylene adipate-co-terephthalate) mulch film on soil microbial communities and tobacco growth

Long-term use of conventional polyethylene mulch film (PE) causes white pollution, whereas biodegradable poly(butylene adipate-co-terephthalate) (PBAT) mulch film can serve as an alternative to PE mulch film. However, research on the effects of long-term residual PBAT mulch film on soil microbial communities and tobacco growth remains limited. In this five-year field experiment, we compared the annual PBAT mulch treatment with a single-dose PE film treatment and a non-mulching blank control (N) to explore their effects on soil microbial communities and tobacco growth. Scanning electron microscope results indicated that the surface of the PBAT mulch film was relatively rough and exhibited varying degrees of cracking and bulging. Further chemical structural analysis revealed that the ester bonds in PBAT broke, the alkyl chains degraded, and oxygen‑containing functional groups were generated. Compared with the other treatments, the long‑term persistence of PBAT residues improved the soil’s physicochemical properties and significantly increased the Shannon and Chao1 indices for bacteria and fungi. At the phylum level, the PBAT treatment increased the relative abundances of Proteobacteria, Actinobacteriota, and Ascomycota, whilst at the genus level, it led to the enrichment of bacteria such as Sphingomonas. Within the fungal community, the proportion of saprophytic fungi increased, whilst the relative abundance of the pathogenic Fusarium decreased. Functional prediction indicated that, in the later stages of the PBAT treatment, the relative abundance of metabolic pathways involved in the degradation of exogenous substances increased, whilst saprophytic fungal functions were enhanced and plant‑pathogenic functions were suppressed. Furthermore, long‑term persistence of PBAT residues had a positive effect on the plant height, stem diameter and maximum leaf area of tobacco. Overall, our results suggest that the long‑term persistence of PBAT residues has positive effects on soil microbial communities and tobacco growth.