Mineral-ions modified biochars enhance the stability of soil aggregate and soil carbon sequestration in a coastal wetland soil

Abstract Biochar (BC) has been evidenced as an effective material to enhance the soil capacity of carbon (C) sequestration. However, the influence of mineral ion-modified BC on soil organic carbon (SOC) mineralization in coastal wetland soil are still unclear. In the present study, a 90 d incubation experiment of a coastal wetland soil incubated with reed straw (RS) and its derived BCs without or with mineral ion modification, was conducted to explore the effects of different BCs on SOC mineralization. The C mineralization in most of the mineral ion-modified BC treatments demonstrated the significant lower levels than the RS and pristine BC treatments. Furthermore, the negative priming effects on soil C mineralization were observed for Fe-modified BCs due to their significant lower C mineralization levels than the control. Meanwhile, the stability of soil aggregate and the proportion of organic carbon (OC) contained in large aggregates (0.25–1 mm) were improved more effectively by the mineral ion-modified BCs, indicating the positive stabilization mechanism of SOC. Moreover, the high content of stable SOC and low pH in soil amended with Fe-modified BCs co-contributed a distinct shift of microbial community from the labile-C preferential bacterial phyla-dominant (e.g., Proteobacteria and Bacteroidetes) to recalcitrant-C preferential bacterial phylum-dominant (e.g., Firmicutes) community. This change may be beneficial to a long-term sequestration of C in soil. In sum, this study demonstrated that the application of mineral ion-modified BC in coastal wetland soil could bring the great potential to restore the C sink function of degraded wetland system.