Responses of phenanthrene degradation to the changes in bioavailability and microbial community structure in soils amended with biochars pyrolyzed at low and high temperatures

This study investigated the impact of wheat straw biochars pyrolyzed at temperatures of 100?700 ?C (BC100BC700) on biodegradation of phenanthrene in soils. During a 42-day experiment, biochar amendment reduced the biodegradation ratio of phenanthrene in soils by no change-77.0%. The biodegradation ratio decreased with the increase of pyrolysis temperature from 100 to 400 ?C and then increased with the increase of pyrolysis temperature from 400 to 700 ?C, exhibiting a U-shape. Meanwhile, desorbing fraction of phenanthrene extracted by n-butanol declined with increasing pyrolysis temperature. Biochar-derived dissolved organic carbon (DOC) obviously influenced the soil DOC contents which were negatively correlated with the total relative abundances of dominant polycyclic aromatic hydrocarbon (PAH)-degraders. These results indicated that in soils amended with biochars pyrolyzed at low temperatures (i.e. 100?400 ?C), both the reduced bioavailability of phenanthrene and the reduced PAH-degrader abundance resulted in decreasing phenanthrene degradation with pyrolysis temperature. In soils amended with biochars pyrolyzed at high temperatures (i.e. 500?700 ?C; HT-biochars), two possible reasons contribute to increasing phenanthrene degradation with pyrolysis temperature: (1) high sorbedphenanthrene concentration due to large specific surface area and high aromaticity of the biochars, and (2) the increased dominant PAH-degrader abundance for the removal of sorbed-phenanthrene due to the impact of HTbiochars on soil properties (mainly on DOC content).

Automated summary

The study found that in soils amended with biochars pyrolyzed at low temperatures, the degradation of phenanthrene decreased with the increase of pyrolysis temperature. On the other hand, in soils amended with biochars pyrolyzed at high temperatures, the degradation of phenanthrene increased with the increase of pyrolysis temperature.