Three years of biochar amendment alters soil physiochemical properties and fungal community composition in a black soil of northeast China

Although biochar amendment has been extensively evaluated as a promising strategy to improve soil quality, most evaluations have been conducted in the laboratory or under short-term field conditions, which restricted us to understand the long-term effects of biochar as a soil amendment. As the residence time of biochar in soils is expected to be hundreds to thousands of years, this study focused on revealing whether biochar addition influences soil physiochemical properties and fungal community composition in a black soil of northeast China over the long term. Biochar was added to the micro-plots at 0%, 2%, 4%, and 8% of the total mass of the top 20 cm of the soil in the spring of 2012, and soil samples were collected seasonally four times in 2014. The results indicate that soil pH, moisture, total C, total N, total P, NO3−-N, available K and the C/N ratio significantly increased but soil bulk density and total K content decreased with biochar addition. The soil fungal abundance determined using quantitative real-time PCR showed that the number of fungal ITS gene copies increased with biochar addition. The soil fungal community composition determined using the Illumina MiSeq sequencing method showed that community diversity was not influenced by biochar addition but the community composition was influenced. The impact of biochar on changes in community composition was not reflected at the phylum level, but at the genus and operational taxonomic units (OTU) levels. The relative abundance of Fusarium decreased, but Guehomyces increased with biochar addition over the first three sampling dates. The relative abundances of several OTUs classified as potential crop pathogens decreased with biochar addition, suggesting that biochar amendment may be beneficial in terms of suppressing the occurrence of crop disease over the long term. In addition, canonical correspondence analysis indicated that fungal community composition was associated with soil parameters such as pH, soil moisture, total C, total N, total K and available K. The changes in these soil characteristics were highly correlated with the amounts of biochar addition, suggesting that the impacts of long-term biochar amendment on the soil fungal community occurred indirectly as a result of the alteration of soil physiochemical properties.