Biochar affects greenhouse gas emissions in various environments: A critical review.

Biochar application to the soil is a novel approach to carbon sequestration. Biochar application affects the emission of greenhouse gases (GHGs), such as CO2, CH4, and N2O, from different environments (e.g., upland soils, rice paddies and wetlands, and composting environments). In this review, the effect of biochar on GHGs emissions from the above three typical environments are critically evaluated based on a literature analysis. First, the properties of biochar and engineered biochar related to GHGs emissions was reviewed, targeting its relationship with climate change mitigation. Then, a meta‐analysis was conducted to assess the effect of biochar on the emissions of CO2, CH4, and N2O in different environments, and the relevant mechanisms. Several parameters were identified as the main influencing factors in the meta‐analysis, including the pH of the biochar, feedstock type, pyrolysis temperature, biochar application rate, C/N ratio of the biochar, and experimental scale. An overall suppression effect among different environments was found, in the following order for different greenhouse gases: N2O > CH4 > CO2. We conclude that biochar can change the physicochemical properties of soil and compost in different environments, which further shapes the microbial community in a specific environment. Biochar addition affects CO2 emissions by influencing oligotrophic and copiotrophic bacteria; CH4 emissions by regulating the abundance of functional genes, such as mcrA (a methanogen) and pmoA (a methanotroph); and N2O emissions by controlling N‐cycling functional genes, including amoA, nirS, nirK, nosZ. Finally, future research directions for mitigating greenhouse gas emissions through biochar application are suggested. [ABSTRACT FROM AUTHOR]