Comparative microbial responses and degradation characteristics of petroleum-based and biodegradable chainsaw...

Chainsaw lubricating oils used during timber harvesting can introduce petroleum hydrocarbons into forest soils, yet their ecological impacts under operational conditions and during natural attenuation remain poorly understood. We conducted a one-year field study comparing commercial biodegradable, mineral, and recycled oils, focusing on hydrocarbon persistence and soil bacterial community responses following harvesting. Total petroleum hydrocarbon (TPH) concentrations remained elevated in soils treated with mineral and recycled oils after one year, whereas TPH in biodegradable oil-treated soils returned to levels comparable to the control. In contrast, priority polycyclic aromatic hydrocarbons showed no consistent accumulation across treatments. Bacterial communities across all treatments shared a conserved taxonomic core, and α-diversity did not differ significantly among oil types. Temporal dynamics dominated community patterns, with γ-diversity increasing over time regardless of lubricant type, indicating progressive taxonomic accumulation during post-harvest natural attenuation. β-diversity analyses revealed modest and transient treatment-associated shifts, with biodegradable oil maintaining greater compositional similarity to control soils over time, while mineral oil showed greater divergence at later stages. Co-occurrence network analysis further indicated oil type dependent reorganization of microbial community structure, with the highest network connectivity observed under mineral oil treatment. Overall, lubricating oil type governed the persistence of petroleum hydrocarbons and the reorganization of soil bacterial community structure during post-harvest natural attenuation.