Comparative metagenomics reveals enhanced nutrient cycling potential after 2 years of biochar amendment in a tropical oxisol

The complex structural and functional responses of agricultural soil microbial communities to the addition of carbonaceous compounds such as biochar remain poorly understood. This severely limits the predictive ability for both the potential enhancement of soil fertility and greenhouse gas mitigation. In this study, we utilized shotgun metagenomics in order to decipher changes in the microbial community in soil microcosms after 14 days of incubation at 23°C, which contained soils from biochar-amended and control plots cultivated with Napier grass. Our analyses revealed that biochar-amended soil microbiomes exhibited significant shifts in both community composition and predicted metabolism. Key metabolic pathways related to carbon turnover, such as the utilization of plant-derived carbohydrates as well as denitrification, were enriched under biochar amendment. These community shifts were in part associated with increased soil carbon, such as labile and aromatic carbon compounds, which was likely stimulated by the increased available nutrients associated with biochar amendment. These findings indicate that the soil microbiome response to the combination of biochar addition and to incubation conditions confers enhanced nutrient cycling and a small decrease in CO₂ emissions and potentially mitigates nitrous oxide emissions.