Changes in Soil Properties and Bacterial Community Composition with Biochar Amendment after Six Years

Changes in soil physicochemical properties and bacterial community composition were investigated six years after biochar amendment at 0%, 4%, 8% and 12% (w/w), which were coded as C0, C1, C2 and C3, respectively. Results showed that some soil characteristics were sustainable, as they were still affected by biochar addition after six years. Compared to the control, biochar-treated soils had higher pH, total carbon (TC), C/N, total nitrogen (TN), available phosphorus (AP) and available potassium (AK). Soil pH, C/N and the content of TC, TN and AK all increased along with the increase of biochar dosage. The results of Illumina MiSeq sequencing demonstrated that biochar enhanced soil bacteria diversity and modified the community composition over time. The relative abundance of Nitrospirae and Verrucomicrobia phylum increased but that of Acidobacteria phylum decreased significantly in biochar amended soils. The addition of biochar also enriched some bacterial genera, such as uncultured Nitrosomonadace, uncultured Gemmatimonadac, uncultured Nitrospiraceae and Magnetovibrio. In particular, the relative abundance of uncultured Nitrospiraceae was enhanced by 16.9%, 42.8% and 73.6% in C1, C2 and C3, respectively, compared to C0. Biochar has a potential role in enhancing the abundance of bacteria involved in N cycling. Soil pH, TC, TN, TK and AK, were closely related to alterations in the composition of the soil bacterial community. Meanwhile, these soil properties were significantly influenced by biochar amendment, which indicates that biochar affected the soil microbial community indirectly by altering the soil characteristics in the long term.