Impact of various concentrations of crude oil on fungal populations of soil

The effect of various concentrations of crude oil on fungal populations of soil was investigated for a period of 18 weeks using standard methods. Total fungal counts ranged from 26 to 143 × 10² cfu/gsoil while counts of petroleum-utilizing fungi ranged from 2 to 102 × 10² cfu/g soil. Analysis of variance and randomized complete block design of counts of total fungi and petroleum-utilizers showed high significant difference between the control and the oil treated soils at p ≤ 0.05 level. Counts of petroleum-utilizers expressed as a percentage of the corresponding total fungal count of the soils ranged from 4.7 % to 58.8 %. Species of fourteen fungal genera were isolated from the soils. These include Alternaria, Aspergillus, Candida, Cephalosporium, Cladosporium, Fusarium, Geotrichum, Mucor, Penicillium, Rhizopus, Rhodotolura, Saccharomyces, Torulopsis and Trichoderma. Of these, ten were petroleum-utilizers and were all isolated from the control and 1 % oil treated soils. Only seven genera were isolated from the 5 % oil treated soil out of which five genera were petroleum-utilizers in both the 3 % and 5 % treatment. The decreasing order of occurrence of a variety of fungal genera (fungal diversity) of both total fungi and petroleum-utilizers is 0 % (control) > 0.5 % > 1 % > 3 % > 5 %. This order of fungal diversity is a reverse of the decreasing order of fungal counts of these same soils. This showed that higher concentrations of crude oil has adverse effect on fungal diversity while enhancing the population of a fewer fungi.