ESTCP Project #1011, Rhizosphere
Final Report
the degradation on some petroleum fractions relative to control treatments (Reynolds et al.,
2001). Whyte et al., 1997, found Pseudomonas spp., isolated from cold soils could degrade C5 to
C12 aliphatics, toluene, and naphthalene at both 5 and 25 C, and also possessed both the alkane
and naphthalene degradation pathways. Their data indicated that both alkane and naphthalene
degradation capabilities, which are located on separate plasmids, can naturally coexist in the
same bacterium. Our earlier work at Fairbanks showed that the dominant culturable bacteria in
both control and fertilized soils were Pseudomonas spp. (Reynolds and Wolf, 1999). The
mechanisms for fertilizer inhibition of heavier fractions are not clear, but we have observed this
in several field studies.
4.3.6 Microbial Characterization. Because the potential for successful remediation of
petroleum-contaminated soils is determined by the number and activity of the hydrocarbon-
degrader microbial population in the soil, we also assessed the influence of fertilizer addition and
vegetation on culturable microbial numbers in a petroleum-contaminated soil at all three sites.
Using culturable microorganisms as a monitoring variable, significant treatment effects were
seen only at the Annette Island site. Soil samples were collected four times over a period of 20
months and total plate counts were used to enumerate bacteria and fungi. The bacterial numbers
significantly increased as a result of fertilizer addition and fungal numbers increased following
the establishment of vegetation (Figure 36). Bacteria but not fungi responded to fertilization.
Fungi but not bacteria responded to plants (Figure 37). The results indicated that adding fertilizer
and establishing vegetation increased microbial populations differentially and the potential for