The Charosphere Promotes Mineralization of 13C‐Phenanthrene by Psychrotrophic Microorganisms in Greenland Soils

• Published in: Journal of environmental quality 2019-05, Vol.48 (3), p.559-567
• Main Authors: Karppinen, Erin M., Mamet, Steven D., Stewart, Katherine J., Siciliano, Steven D.
• Format: Article
• Language: English
• ISSN: 0047-2425; 1537-2537
• DOI: 10.2134/jeq2018.10.0370

When soil is frozen, biochar promotes petroleum hydrocarbon (PHC) degradation, yet we still do not understand why. To investigate microbial biodegradation activity under frozen conditions, we placed 60‐μm mesh bags containing 6% (v/v) biochar created from fishmeal, bonemeal, bone chip, or wood into PHC‐contaminated soil, which was then frozen to −5°C. This created three soil niches: biochar particles, the charosphere (biochar‐contiguous soil), and bulk soil outside of the bags. After 90 d, 13C‐phenanthrene mineralization reached 55% in bonemeal biochar and 84% in bone chip biochar charosphere soil, compared with only 43% in bulk soil and 13% in bone chip biochar particles. Soil pH remained near neutral in bone chip and bonemeal biochar treatments, unlike wood biochar, which increased alkalinity and likely made phosphate unavailable for microorganisms. Generally, charosphere soil had higher aromatic degradative gene abundances than bulk soil, but gene abundance was not directly linked to 13C‐phenanthrene mineralization. In bone chip biochar‐amended soils, phosphate successfully predicted microbial community composition, and abundances of Bosea and Caulobacter increased in charosphere soil. Biochar effects on charosphere soil were dependent on feedstock material and suggest that optimizing the charosphere in bone‐derived biochars may increase remediation success in northern regions. Core Ideas 13C‐phenanthrene was mineralized in the charosphere of bone chip biochar particles. pH and nutrient availability were dependent on biochar type and sampling location. Biochar effects are localized in specific spatial niches of the soil.