| Biochar is generally considered playing a vital role on carbon sequestration in soil ecosystem, as well as on feitility retaintion and pollutants remediation. Soil microorganisms interact with the introduced biochar, which on the one hand affects the stability of bichar and on the other induces the changes in soil microbial community as well as functional traits.Both the abundance and diversity of soil microorganisms in soils are influenced by a variety of abiotic and biotic variables. The effect of biochar on the microbial community has been reported, but the underlying mechanisms modifying soil microbial distribution are less understood. In the test 1, biochar is physically separated from soil and the abiotic characteristics generally recognized influencing soil microbial communities are examined. The microbial community structure is assessed via denaturing gradient gel electrophoresis (DGGE). The influence of abiotic components including available N, Olsen P, extractable K, pH and C/N induced by biochar on soil microbial communities are compared by canonical correspondence analysis (CCA). Results indicate that biochar fosters more fungi and stimulates bacteria growth in the adjacent soil. Biochar particles at three sampling times exhibit the similar microbial community composition, although it is also impacted by temporal factors. Phylogenetic distributions of the operational taxonomic units (OTUs) could be divided into the following 8 groups:Bacillaceae, Gemmatinomadetes, Sphingomanas, Acidobacteria, Proteobacteria, Chloroflexaceae, Actibacteria (similarity> 95%) and unknown (similarity< 85%). Canonical correspondence analysis (CCA) reveals the greater contribution of C/N, Olsen P and extractable K to fungi growth, and C/N and Olsen P to actinomycete abundance. The presence of biochar not only induces the increase of available nutrients, but also increases microbial biomass and diversity, which indicates beneficial effects on soil microorganisms and soil fertility.Biochar is considered difficult for microorganisms to decompose, whereas the volatile organic compounds (VOCs) sorbed onto fresh biochar may affect the survival rate of inoculants or the structure of soil microbial communities.It is hypothesed that VOCs on fresh biochar may play a vital role on shaping the structure of soil microbial communities and determining if inhibited or supported the growth of inoculants. In the test 2, 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 is examined. The composition of VOCs before and after the incubation is characterized by pyrolysis-gas chromatography/mass spectroscopy (Py-GC-MS). The structure of a whole suspension of soil microbial community incubated in biochar is examined via denaturing gradient gel electrophoresis (DGGE). Canonical correspondence analysis (CCA) is applied to reveal the contribution of potential factors such as pH, K and Na, and diversity indices from VOCs fingerprints to the diversity indices calculated from DGGE profiles. Results show that all biochars are able to support Bacillus mucilaginosus at population densities analogous to peat. Phenols, comprising 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 rDNA and 18S rDNA DGGE profiles is greatly affected by biochar. Besides, CCA reveals the role of VOCs in shaping the structure of soil microbial communities. VOCs absorbed to biochar, despite their short lifespans, could support the survival of Bacillus 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.Despite a growing body of evidence suggesting that biochar changes the structure of soil microbial communities, little evidence has revealed the long-term effect, and which may be linked to the role of old black carbon (BC) in soil ecosystem. In the test 3, pyrolysis-gas chromatography/mass spectroscopy is used to analyze the composition of pyrolysates in biochar pellets. Also, the structure of soil microbiome is examined by using 454 Pyrosequencing and the activities of bacteria and fungi are contrasted by measuring their biomarkers.In addition, the functions of the bacterial community are predicted by Phylogenetic Investigation of Communities by Reconstruction of Unobserved States analysis. The composition of pyrolysates in biochar pellets has changed during soil aging. The enhanced abundance of muramic and decreased ratio of glucosamine to muramic acid are found in biochar pellets. The structure of bacterial community is more shifted by biochar compared with the fungal community. The bacterial metabolism capacities in xenobiotics are enhanced, which may be associated with the presence of organic carbons analogous to xenobiotics in biochar. The decreased capacity of bacterial community in metabolizing carbohydrates explains the high abundant water soluble carbon occurred in biochar pellets. Both of our results and previous findings indicate biochar or BC could drive the microbial community toward high C metabolic quotient. As BC comprises similar components to biochar, it is speculated that biochar may mirror the role of BC in the soil microbial communities. Therefore, BC may alter the C metabolism of soil bacterial communities.Altogether, biochar could influence the soil microbial communities via abiotic pathways, but for fresh biochar, the volatile organic carbon outweighs other variables on affecting soil microbial community. The microbial activities not only result in decomposing the labile organic carbon in fresh biochar, but also drive the structure loose of intermediate stable organic carbon.Both labile organic carbon and decomposed moderate in biochar are considered affecting the metabolic traits, such as increased capacity in degration of xenobiotics and decreased capacity in utilizing carbohydrates. The findings here are possibly providing the evidence how biochar maintains the soil fertility. In addition, biochar has exhibited potential as being used as carriers for inocullants as well as being as a vehicle for soil pollutants remediation. |
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