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Application of biochar derived from biomass resources in soil is an encouraging method to decelerate global warming via carbon sequestration. While there has been extensive research on the priming effect of biochar on the mineralization of native soil organic carbon (nSOC), its correlation with soil organic carbon (SOC) structural variations remains poorly understood. A series of incubation experiments with soils amended with biochar prepared at 300 °C, 450 °C, and 600 °C were performed to explore the shifts in nSOC structure and reveal the interconnections among soil properties, SOC structural variation, and the priming effect induced by biochar. Biochar exhibited an "inhibitory concentration" on soil microorganisms, where 1 % biochar enhanced bacterial and fungal richness and diversity, while 3 % biochar reduced bacterial richness and diversity although soil nutrient conditions were improved. Biochar-treated soil had higher humic acid- and humin-like fractions (HAL and HML) but lower fulvic acid-like components (FAL). Moreover, bulk SOC, FAL, HAL, and HML of soils with 300 °C and 450 °C biochar contained more aromatic-type species (e.g., lignin). Such changes were related to improvement of the soil nutrient condition and shifts in microbial community structures, in addition to the "accumulation of biochar-derived OC in the nSOC pool". Stable carbon isotopes indicated that the inhibitory effect on SOC mineralization (−94.5 to −8.0 mg CO 2 -C kg−1 soil) induced by biochar was significantly explained by the change in FAL and HAL contents. The findings improved the understanding of the carbon sequestration potential of biochar in soils for SOC structural modification. • Biochar showed an "inhibitory concentration" on soil microorganisms. • Biochar-added soils contained more humic acid- and humin-like fraction. • Structure change in SOC was related to soil nutrient and biological condition shift. • Increase in stable SOC partly explained the negative priming effect of biochar. [ABSTRACT FROM AUTHOR]

[Display omitted] • Aggregate stability was dropped by MPs, due to the decline of adhesive agents. • Bacterial community of microaggregates were more sensitive to MPs. • PE MPs more strongly exacerbated bacterial competition and network complexity. • Proteobacteria, Actinobacteria, and Chloroflexi were the sensitive bacteria to MPs. Microplastics (MPs), including conventional hard-to-biodegrade petroleum-based and faster biodegradable plant-based ones, impact soil structure and microbiota in turn affecting the biodiversity and functions of terrestrial ecosystems. Herein, we investigated the effects of conventional and biodegradable MPs on aggregate distribution and microbial community composition in microhabitats at the aggregate scale. Two MP types (polyethylene (PE) and polylactic acid (PLA) with increasing size (50, 150, and 300 μm)) were mixed with a silty loam soil (0–20 cm) at a ratio of 0.5 % (w/w) in a rice–wheat rotation system in a greenhouse under 25 °C for one year. The effects on aggregation, bacterial communities and their co-occurrence networks were investigated as a function of MP aggregate size. Conventional and biodegradable MPs generally had similar effects on soil aggregation and bacterial communities. They increased the proportion of microaggregates from 17 % to 32 %, while reducing the macroaggregates from 84 % to 68 %. The aggregate stability decreased from 1.4 mm to 1.0–1.1 mm independently of MP size due to the decline in the binding agents gluing soil particles (e.g., microbial byproducts and proteinaceous substances). MP type and amount strongly affected the bacterial community structure, accounting for 54 % of the variance. Due to less bioavailable organics, bacterial community composition within microaggregates was more sensitive to MPs addition compared to macroaggregates. Co-occurrence network analysis revealed that MPs exacerbated competition among bacteria and increased the complexity of bacterial networks. Such effects were stronger for PE than PLA MPs due to the higher persistence of PE in soils. Proteobacteria, Bacteroidetes, Chloroflexi, Actinobacteria, and Gemmatimonadetes were the keystone taxa in macroaggregates, while Actinobacteria and Chloroflexi were the keystone taxa in microaggregates. Proteobacteria, Actinobacteria, and Chloroflexi were the most sensitive bacteria to MPs addition. Overall, both conventional and biodegradable MPs reduced the portion of large and stable aggregates, altering bacterial community structures and keystone taxa, and consequently, the functions. [ABSTRACT FROM AUTHOR]