ECOLOGICAL IMPACTS OF pH, WATER AND OIL ON MICROBIAL COMMUNITIES IN CRUDE OIL-CONTAMINATED SOILS FROM FIVE OIL-FIELDS IN CHINA

The microbial communities and physico-chemical parameters of crude oil-contaminated soils sampled from five oil-fields in China were analyzed using a polyphasic approach. The objective was to determine any ecological effects of abiotic factors, such as nutrient level, soil pH, pollutant level, and moisture on microbial communities in the soils. Results showed that soil pH was an important factor affecting microbial communities in the contaminated soils. Results showed that microbial populations were generally low when soil pH was higher than 8.0; in detail, the density of oil degrading micro-organisms was less than 104 cells.g(-1) dry soil, fluorescein diacetate (FDA) activity was less than 0.4 abs.g(-1) dry soil.h(-1), and H was smaller than 0.7. When soil pH was between 7.0 and 8.0, water content and pollutant level were important factors affecting microbial communities. For water contents between 6-13% and oil content less than 8%, the total microbial density was higher than 108 cells.g-1 dry soil, FDA activity was above 0.3 abs.g(-1) dry soil.h(-1), and H was greater than 0.9. The relative abundance of oil degrading micro-organisms relative to total micro-organisms was highest when the oil content was 3-8%, which may be optimal for the proliferation of oil degrading bacteria. The correlation analysis between nutrient level and microbial community revealed that there was no obvious influence of effective nitrogen (EN) or effective phosphorus (EP) on the microbial communities in the oil-field soil environment.