Oil and wildfire effects on nutrient cycling and microbial diversity in subarctic mineral soils

Abstract

In 1976 crude oil was experimentally spilled on a plot near Fairbanks, Alaska to mimic an oil pipeline spill. The plot and surrounding area were further disturbed by wildfire in 2004. Although the fire burned organic matter on the plot surface, substantial subsurface oil remained. After the fire, soil samples from oiled/burned, burned, and control plots were collected to evaluate the effects of disturbance on nutrient cycling and soil bacterial communities. Samples were analyzed for total nitrogen (N), soil carbon (C) and N mineralization, N fixation, total bacterial diversity (16S rDNA), and functional genetic diversity (nifH). Inorganic N was low in all soil types. In control and burned soils there was net N mineralization, but in oiled/burned soils there was significant N immobilization. Carbon mineralization was much higher in oiled/burned soils than control or burned soils. While the highest N fixation potential was measured in oiled/burned soils, the diversity of the N-fixing bacterial community in those soils was about the same as that of the control. For 16S rDNA, diversity was higher in control and burned soils than in oiled/burned soils. Overall, the type of disturbance and the length of time since disturbance both affected microbial function and diversity