Abstract: Biochar has been widely applied as a soil amendment in many parts of the world, which can enhance soil organic carbon (SOC) sequestration and nutrient availability beyond the fertilizer effect.  Enriched in poly-condensed aromatic C forms, biochar-C is difficult to be degraded and can hold carbon in soils for hundreds to thousands of years.  Biochar production and incorporation in soil would play critical roles in climate change mitigation.  Over the last decades, numerous researches have highlighted the beneficial roles of biochar in soil amendments.  The specific ecological functions of biochar have not been clearly described because of its diversities and complexities.  For example, biochar helps to ameliorate soil acidity and increase soil aggregated carbon, but the role of microbial interactions between biochar and soil has not been well understood.  In this special issue, we selected four papers contributed by Yuan et?al. (2019), Chen et?al. (2019), Guan et?al. (2019) and Shi et?al. (2019), as a window to reflect the latest research progress of this field in China.  Yuan et?al. (2019) investigated the diversity of microbial carbon use patterns in paddy soils amended with straw or straw-derived biochar in a 3-year field experiment; Chen et?al. (2019) reported that steam explosion of crop straws could improve the characteristics of biochar; Guan et?al. (2019) evaluated the effects of uncharred maize straw and charred maize straw amendments on organic carbon contents in bulk soil and in various soil aggregate-size and density fractions; Shi et?al. (2019) summarized the positive effects and mechanisms involved in the correction of soil acidity, the alleviation of aluminum toxicity and the increase of soil pH buffering capacity by applying crop residue biochar.  Through this special issue, we hope to further boost the basic and applied researches with related to the ecological functions of biochar from different aspects in soil in China and abroad.