Changes of bacterial community compositions after three years of biochar application in a black soil of northeast China

Although biochar has been widely evaluated as a soil-amendment, the response of soil bacterial community to biochar addition, especially after several years' addition, has not yet been fully understood. Here, we studied the effect of a single addition of biochar on bacterial community compositions in a black soil of northeast China. The biochar was added with dosages of 0%, 2%, 4% and 8% of the total mass of the top 20 cm soils in the spring of 2012, and soil samples were collected seasonally four times in 2014. The abundance and composition of bacterial community were determined using quantitative real-time PCR and Illumina MiSeq sequencing methods, respectively. The results showed that soil pH, moisture, total C, total N, total P, NO3−-N, available K and the C/N ratio significantly increased with biochar addition, but that soil bulk density and total K content decreased. The bacterial abundance increased with biochar addition, especially at a higher dosage. The biochar addition increased the alpha-diversity of soil bacterial community and changed the bacterial community compositions. Taxonomic analyses showed that Proteobacteria, Acidobacteria, Actinobacteria, Chloroflexi and Bacteroidetes were the dominant phyla in this study, and the relative abundances of Acidobacteria decreased but Chloroflexi increased with biochar addition. Additionally, biochar addition increased the relative abundances of Bacillus and Pedomicrobium, but decreased the relative abundance of Bradyrhizobium. Canonical correspondence analysis indicated that bacterial community compositions were closely associated with soil parameters such as pH, total C, total N and total K. Given the changes of these soil parameters were highly correlated with the amounts of biochar addition, which suggested that the impacts of long-term biochar amendment on the soil bacterial community were linked to the alteration of soil physiochemical properties.