Greenhouse gas emissions and soil bacterial community as affected by biochar amendments after periodic mineral fertilizer applications

In a 338-d microcosm incubation experiment, greenhouse gas emissions (GHG) and bacterial diversity were studied in a clayey soil amended with 5% (w/w) biochar in the presence or absence of 4% (w/w) peat- and shrimp-based compost used as an additional C source. Two maple biochars produced at 400 °C (M400) or 700 °C (M700) and pine chips produced at 700 °C (P700) were tested. In comparison with soil supplemented or not with compost, the addition of any biochar resulted in lower total cumulative N 2 O emission (90% to 97%). The low porosity of M400 and M700 increased soil anaerobic conditions and resulted in higher total cumulative CH 4 emission compared to the other soil treatments. In addition, the lowest total cumulative CO 2 emission was observed with M700, probably due to its low-priming effect on native soil C decomposition. In all treatments, compost addition had the highest impact on both soil bacterial richness and community composition, particularly on bacteria of the class Anaerolineae . At day 338, results showed that modification of soil properties by maple biochars reduced bacterial diversity and induced shifts in the taxonomic composition of their community. In fact, heterotrophic bacteria involved in denitrification, such as genera Haliangium , Hyphomicrobium , Opititus , and Pedomicrobium , increased in abundance in response to the amendment with maple biochars. We conclude that the nature of biochar feedstock can impact soil bacterial diversity by changing soil physicochemical properties, thus influencing C dynamics, porosity, and pH, and by mitigating total cumulative GHG emissions.