Introduction Since biochar has the potential to mitigate climate change and enhance agricultural outputs, new research is exploring its dual role relative to greenhouse gas emissions from agronomic soils, with particular focus on nitrous oxide (N2O). It is well accepted that definitive investigations of sustainable contemporary biochar applications in different (bio)technologies must be underpinned by combined physico-chemical and microecophysiological analyses. Nevertheless, recent nitrogen cycle research has measured principally the occurrence and emission of different N species to then infer shifts in microbial activity in response to biochar augmentation, with a few emerging studies assessing its effects on the functional genes/communities. As a result, a wide scope for critical and exciting research exists. This must be informed by comprehensive multidisciplinary studies of the dynamics of functional N-cycle genes, enzymes, strains and communities across different ecosystems and environmental biotechnologies – agriculture, contaminant remediation, wastewater treatment, malodorant gas biofiltration and landfill. This review aims to summarize the state-of-the art and highlight critical research that is required to assess the effect of biochar addition on N-cycling in different ecosystems. Conclusion We conclude that despite emerging research there are still critical knowledge gaps on the microbial response to biochar, which need to be addressed before the material can be applied in specific key environmental biotechnologies
