Effect of volatile organic compounds absorbed to fresh biochar on survival of Bacillus mucilaginosus and structure of soil microbial communities

Biochar is considered difficult for microorganisms to decompose, and volatile organic compounds (VOCs) sorbed to fresh biochar may affect the survival rate of inoculants or the structure of soil microbial communities. We tested the hypotheses that VOCs on fresh biochar may play a vital role in shaping the structure of soil microbial communities and determined if they inhibited or supported the growth of inoculants. We examined the growth of Bacillus mucilaginosus in mushroom medium-based biochar (MM-biochar), corn stalk-based biochar (CS-biochar), and rice straw-based biochar (RS-biochar) in comparison with peat. The composition of VOCs before and after the incubation was characterized by pyrolysis-gas chromatography/mass spectroscopy (GC-MS). The structure of a soil microbial community incubated in biochar was examined via denaturing gradient gel electrophoresis (DGGE). Canonical correspondence analysis (CCA) was applied to reveal the contribution of pH, K and Na, and diversity indices from VOC fingerprints to diversity indices in DGGE profiles. In the present study, all biochars were able to support B. mucilaginosus at population densities analogous to peat. Phenols comprise a fraction of the VOCs that potentially could be toxic to some microbes and inhibit their growth in the short time. The structure of the inoculated soil microbial communities in terms of the diversity indices calculated from 16S ribosomal DNA (16S rDNA) and 18S rDNA DGGE profiles was greatly affected by biochar. Besides, CCA revealed the role of VOCs in shaping the structure of soil microbial communities. VOCs absorbed to biochar, despite their short life spans, could support the survival of B. mucilaginosus, demonstrating the potential of biochars as carriers for inoculants. The changes in the soil microbial communities induced by fresh biochar may not represent the long-term biochar effect. Therefore, future work needs to appreciate mechanisms underlying aged biochar on the structure of soil microbial communities.