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 CO 2 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 CO 2 emissions. PE decreased the CO 2 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 CO 2 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. • Minerals led to the shift of bacteria from r-to K-strategists in biochar (BC). • Quartz preserved aromatic C while smectite preserved aliphatic C in BC. • Kaolinite preserved aromatic/aliphatic C in BC. • Polyethylene promoted the accumulation of aromatic C in BC-mineral association. • Polyethylene increased CO 2 emission of biochar-mineral system due to fungi shift.