Biochar application enhances ant (Formica japonica) ecological functions as indicated by their social behaviors

Abstract Soil fauna activity is crucial for soil ecosystem functioning and health, but soil remediation techniques, such as biochar application, are seldom examined for their influence on soil fauna activity. This study systematically evaluated the effects of rice straw biochar application on the social behaviors of ants, Formica japonica , and elucidated how these behavioral changes enhance ant ecological functional traits. At moderate concentrations (2.5–5%), biochar significantly enhanced several ant colony functions: nest site selection specificity increased by 73.4%, nest architecture complexity improved by 2.8-fold, foraging efficiency accelerated by 2 fold, and social recognition accuracy enhanced by 3.5-fold. The improved colony performance was manifested through sophisticated behavioral responses, including strengthened territorial defense (3.5-fold increase in aggressive behavior duration) and enhanced intraspecific cooperation (4 fold increase in peaceful touch frequency). These behavioral enhancements coincided with specific soil physicochemical conditions at the application rate of 5% biochar. However, higher biochar doses (10%) reduced colony-level survival to 60 ± 5.44% and diminished functional enhancement of behavioral performance, in part due to the presence of persistent free radicals and high pH. Our results indicate that ant social behavior may be altered during soil remediation, which should be carefully considered prior to engineering practices. Graphical Abstract