The preferential preservation of both different minerals and polyethylene microplastics on aromatic or aliphatic carbon fractions within low or high pyrolysis temperature biochar under mineralization

The effects of soil minerals and microplastics on the stability of biochar (BC) have not been clearly clarified. Here, the mineralization of BC produced at low and high temperatures (L-BC and H-BC) and their artificial soils made of quartz, smectite and kaolinite, respectively, was investigated. BC and BC artificial soils were incubated with or without polyethylene (PE) over 180 d, and the CO2 emission, molecular composition and microbial community structure were assessed. Minerals, especially quartz, had relatively more protection to H-BC than to L-BC. Moreover, smectite preserved aliphatic C of L-BC, and kaolinite protected its aromatic C and aliphatic C. Smectite and kaolinite likely had comparable ability to protect BCs. Quartz protected the aromatic C of H–BCs by adsorbing the hydrophobic aromatic C. Minerals also led to the shift of the dominant bacteria from r-strategists to K-strategists, which alleviated degradation of labile carbon and reduced the CO2 emissions. PE decreased the CO2 emissions of L-BC as well as its artificial soils and the opposite effect was observed for H-BC. PE enhanced the aromatic C associated with minerals within H-BC artificial soils, and inhibited the mineralization of H-BC. PE degradation by fungi (Aspergillus) could be largely responsible for the rise in CO2 emissions of H-BC artificial soils. This study addressed the different effect of minerals and PE in the process of BC mineralization and provided the basis for elucidating the stability mechanism of BC in soil, which would be helpful for establishment of BC carbon sequestration policy.