Purpose The term “charosphere” refers to the biochar-contiguous soil that is directly influenced by the physicochemical properties of the biochar, yet the dynamics of microbial composition in the charosphere in heavy metal-polluted soil remains largely unknown.

Methods Swine manure-derived biochars prepared at 300 and 700 °C were packed in a double-layer mesh bag and then buried in a Cd-contaminated paddy soil for 15 days (T1) and 95 days (T2). Bacterial community composition in the charosphere and the linked properties such as soil pH, dissolved organic carbon (DOC) contents, and total Cd and Zn concentrations were analyzed.

Results The results showed that biochar significantly shifted the beta diversity of the bacterial community in the charosphere, mainly due to increase in pH and total Zn concentrations. Further, 300 °C-prepared biochars stimulated Bacteroidetes and inhibited Acidobacteria by increasing soil pH. In the charosphere of biochars prepared at 700 °C, associated with the release of Zn and the adsorption of Cd, Chloroflexi became favorable over other microbial groups. Both biochar additions gave an increase in the putative function of energy metabolism and lipid metabolism, which might help bacteria dominant in charosphere resist stress of heavy metals.

Conclusion Taken together, these pieces of evidence suggest that bacterial community and potential functions in the charosphere differ remarkably from the control soil without biochar, which was mainly due to biochar reduced environmental stresses such as soil acidity and heavy metals.