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

Abstract

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.

Bacterial community structure and putative nitrogen-cycling functional traits along a charosphere gradient under waterlogged conditions

“…However, few studies have focused on the bacterial community and functional effects, especially in terms of spatial variability across the biochar-soil interactive zone. Novel spatial niches created by biochar form a dynamic biogeochemical zone coupling many interacting processes (Karppinen et al, 2019). This special soil zone surrounding a biochar source is termed the "charosphere" and may extend several millimeters into the adjacent soil (Quilliam et al, 2013;Yu et al, 2019).…”

Manipulation of Unfrozen Water Retention for Enhancing Petroleum Hydrocarbon Biodegradation in Seasonally Freezing and Frozen Soil

“…Previous bioremediation experiments indicate that the presence of unfrozen water is critical for extending hydrocarbon biodegradation in frozen contaminated soil. ,− However, the relationship between the manipulation of unfrozen water retention via controllable soil factors and the enhancement of petroleum hydrocarbon biodegradation is not understood. Unfrozen water content, influenced by a variety of factors, gradually decreases as soils undergo seasonal freezing, before stabilizing at a minimum threshold in deeply frozen soil .…”