Soil Properties and Microbial Community Assemblages in Response to Plastic Film Mulches with Divergent Degradation Characteristics

To identify a suitable plastic film type for broccoli cultivation in the subtropical humid region of southern China, a field experiment was conducted with four treatments, including no film control (CK), reinforced polyethylene film (RF), biodegradable film PBAT + starch (BDF1), and biodegradable film PBAT + PLA (BDF2). Soil physiochemical properties, temperature and humidity dynamics, microbial community structure, and film degradation status were investigated. The results showed that the RF treatment improved available P and K contents, while the BDF2 treatment significantly increased soil organic matter, NH4+-N, water-soluble Ca2+, and Mg2+ contents. The soil temperature followed the order of RF > BDF1 > BDF2 > CK, and the humidity was BDF1 > RF > CK > BDF2, with RF treatment showing a more stable soil temperature, while BDF2 treatment fluctuated the most. There were no significant differences in bacterial diversity among the treatments, while the highest fungal diversity was observed in the BDF2. Water-soluble Mg was the key factor driving the changes in microbial community structure (p < 0.05). The film degradation rate followed BDF2 > BDF1 > RF. Collectively, RF is suitable for targeting short-term yield improvement, while BDF2 has significant advantages in sustainable cultivation in the long-term.