Biochar-induced negative carbon mineralization priming effects in a coastal wetland soil: Roles of soil aggregation and microbial modulation

Biochar can sequestrate carbon (C) in soils and affect native soil organic carbon (SOC) mineralization via priming effects. However, the roles of soil aggregation and microbial regulation in priming effects of biochars on SOC in coastal wetland soils are poorly understood. Thus, a coastal wetland soil (delta C-13-22 parts per thousand) was separated into macro-micro aggregates (53-2000 mu m, MA) and silt-clay fractions (<53 mu m, SF) to investigate the priming effect using two C-13 enriched biochars produced fromcorn straw(delta C-13-11.58 parts per thousand) at 350 and 550 degrees C. The two biochars induced negative priming effect on the native SOC mineralization in the both soil aggregate size fractions, attributed to the enhanced stability of the soil aggregates resulting from the intimate physico-chemical associations between the soil minerals and biochar particles. Additionally, biochar amendments increased soilmicrobial biomass C and resulted in a lower metabolic quotient, suggesting that microbes in biochar amended aggregates could likely incorporate biomass C rather than mineralize it. Moreover, the biochar amendments induced obvious shifts of the bacterial community towards low C turnover bacteria taxa (e.g., Actinobacteria and Deltaproteobacteria) and the bacteria taxa responsible for stabilizing soil aggregates (e.g., Actinobacteria and Acidobacteria), which also accounted for the negative priming effect. Overall, these results suggested that biochar had considerable merit for stabilizing SOC in the coastal soil and thus has potential to restore and/or enhance blue C sink in the degraded coastal wetland ecosystem. (C) 2017 Elsevier B.V. All rights reserved.