PBAT biodegradable microplastics enhanced organic matter decomposition capacity and CO2 emission in soils with and without straw residue

Recent studies show that biodegradable microplastics (BMPs) could increase soil CO emission, but whether altered carbon emission results from modified soil organic matter (SOM) decomposition remains underexplored. In this study, the effect and mechanisms of BMPs on CO emission from soil were investigated, using poly(butylene adipate-co-terephthalate) (PBAT, the main component of agricultural film) as an example. Considering that straw returning is a common agronomic measure which may interact with microplastics through affecting microbial activity, both soils with and without wheat straw were included. After 120 d, 1 % (w/w) PBAT BMPs ificantly increased cumulative CO emission by 1605.6 and 1827.7 mg C kg in soils without and with straw, respectively. Cracks occurred on the surface of microplastics, indicating that CO was partly originated from plastic degradation. Soil dissolved organic matter (DOM) content, carbon degradation gene abundance (such as abfA, xylA and manB for hemicellulose, mnp, glx and lig for lignin, and chiA for chitin) and enzyme activities increased, which significantly positively correlated with CO emission rate (p < 0.05), suggesting that PBAT enhanced carbon emission by stimulating the decomposition of SOM (and possibly the newly added straw) via co-metabolism and nitrogen mining. This is supported by DOM molecular composition analysis which also demonstrated stimulated turnover of carbohydrates, amino sugars and lignin following PBAT addition. The findings highlight the potential of BMPs to affect SOM stability and carbon emission.