Moderating carbon dynamics in black soil by combined application of biochar and an artificial humic substance

The mineralization and humification of organic matter triggered by added exogenous carbon are relevant to soil organic matter (SOM) turnover and stability. Biochar (BC) and artificial humic substance (A‐HS), two typical exogenous carbon materials, have not been jointly applied to seek to improve the soil carbon pool, which is contributed by the development of A‐HS which has not yet been used on a large‐scale. We surmise that the dynamic interactions occurring in combined application of BC and A‐HS are complex and deserve detailed attention. Herein, a continuous incubation experiment including relevant weather events (freezing, freezing–thawing, warming climates) was conducted for 180 days to observe the development of SOM in the different stages and under separate and mixed applications of A‐HS and BC. After 45 d cultivation period and the freezing phase, the relative mineralization rate of SOM was up to 6.4% (120 ml/kg A‐HS), 4.9% (2% BC) and 13.3% (for the combination of 120 ml/kg A‐HS and 2% BC), suggesting that the presence of A‐HS triggers an enhanced mineralization of SOM throughout freezing. However, the remaining SOM turned out to be more strongly humified and more stable, preserving the SOM through the warming season, as shown by ultraviolet fluorescence and high‐throughput sequencing. Overall, the dynamic interactions between BC and A‐HS are shown to be mainly mediated by biological activity and alterations of microbial community structure and the related metabolic preferred pathways, which vice versa can be influenced by the added carbon sources.