Short-term effects of biomass burning on soil ammonia-oxidizing bacteria and ammonia-oxidizing archaea

Biomass burning, a form of disturbance in soil ecosystem, is frequently carried out in farmland after harvest in China, which has potential influence on soil biological properties. To study the short-term effects of biomass burning on soil ammonia-oxidizing bacteria (AOB) and archaea (AOA), a field investigation utilizing poplar branch (PB) and corn stalk (CS) as feedstock for experimental biomass burning was conducted in farmland in Yanqing County, Beijing, China (116°12'E, 40°25'N). The shifts in abundance and community composition of AOB and AOA were investigated utilizing real-time polymerase chain reaction (PCR), cloning and sequencing approaches based on amoA genes. Striking increase in potential ammonia oxidation rate and abundance of soil AOA and AOB after fire were observed, as well as community composition of AOA. For AOB, little changes in diversity but significant shifts in relative abundance of different Clusters were observed after fire. Phylogenetic analyses of the amoA gene fragments showed that all AOB clones from different treatments were affiliated with Nitrosospira species and grouped into 5 clusters (3a, 3b, 3c, A and B). Most of the clones were almost evenly distributed in Cluster 3a, 3b, A and B before burning. However, domination in the clones by Cluster 3a was observed after fire. All AOA clones fell within Soil cluster (soil origin). Although Group 1.1b was found dominant in the obtained AOA clones in all the treatments, the relative abundance of clones belonging to Group 1.1b decreased after fire. These findings could be fundamental to improve our understanding of the effect of biomass burning on soil AOB and AOA in agricultural ecosystems.