Biodegradable Film Mulching Increases Soil Respiration: A Two-Year Field Comparison with Polyethylene Film Mulching in a Semi-Arid Region of Northern China

Biodegradable film mulching is increasingly used to replace polyethylene in agriculture, but effects on soil respiration (SR) and components remain unclear, especially during degradation. This study investigated biodegradable mulching’s regulation of SR, root-derived respiration (RDR), and non-root-derived respiration (NRDR) under varying phases. A two-year field experiment was conducted in a rainfed maize system in northern China, comparing conventional tillage with biodegradable film mulching (BM), conventional tillage with polyethylene film mulching (PM), and conventional tillage without mulching (CT). Continuous measurements of soil CO2 concentration (SCC), temperature, water content, and respiration components were used to assess dynamic responses. Results showed that BM enhanced SR and shifted peak timing, with the SR peaking at 106 days after sowing (DAS) under BM, 91.8 DAS under PM, and 91.2 DAS under CT, mainly through a more sustained RDR (BM peak at 103 DAS with a broader peak and greater cumulative RDR than PM and CT). As the biodegradable plastic film degraded, NRDR was higher during the degradation phase, consistent with a priming-like response. These phase-dependent effects suggest that BM first facilitates root growth then serves as a microbial substrate. Moreover, elevated SCC was positively associated with both RDR and NRDR, indicating that CO2 may function as a regulatory signal rather than a passive byproduct of respiration. These findings reveal distinct temporal mechanisms by which BM influences soil carbon fluxes and offer mechanistic insights into the sustainable application of biodegradable film mulching. Future research should evaluate long-term effects on microbial community composition, soil carbon balance, and potential trade-offs with crop productivity and environmental risks.