Functional diversity of the microbial community in the rhizosphere of chickpea grown in diesel fuel-spiked soil amended with Trichoderma ressei using sole-carbon-source utilization profiles

Present study describes chickpea (Cicer arietinum) growth, microbial activity and community composition in a soil samples spiked with 0, 20 (LCD) and 80 g (HCD) diesel/kg soils, amended with Trichoderma ressei. T. ressei had stimulatory effect on the plant growth parameters as compared with un-inoculated control chickpea plant. Root length, shoot length, plant dry weight and chlorophyll content enhanced 128, 31, 46, 79%, respectively, as compared over the un-inoculated control. At LCD in the presence of T. ressei chickpea root length, shoot length, plant dry weight and chlorophyll content was maximum indicating that at this concentration of diesel chickpea plants could grow very well and T. ressei amendment had synergistic effect. Effect on microbial population was most evident at HCD and resulted in 4.84 log unit reduction of heterogeneous bacterial population, as compared with LCD which caused reduction of 2.8 log unit, compared with non-diesel spiked control soil. Impact of diesel on soil was somewhat lessened in the presence of T. ressei. Our results indicated that application of diesel improved the organic matter status of soils which was in turn reflected in the higher dehydrogenase activity. This could be due to diesel being a good source of hydrocarbon readily available for microbial activity. The structure of the microbial community in rhizosphere was analyzed through the sole-carbon-source utilization profiles using ECO Biolog microplates. Significant differences were found among the diversity and evenness indices on effect of diesel on chickpea rhizosphere microflora in presence and absence of T. ressei, based on Tukey's test (at P = 0.05). Principal component analysis of substrate source utilization pattern on Biolog Eco plates by chickpea rhizosphere microflora in presence and absence of T. ressei was determined. Distinct resolution of soil microbial communities in the presence of either diesel or, T. ressei observed thus revealed differences in the microbial metabolic profiles for the different treatments. Our results demonstrated that characteristics of the dynamics in microbial communities complemented well with organic matter status of soils and dehydrogenase activity. The technique highlighted the usefulness of this parameter for ecological indication of land use change in diesel contaminated ecosystems.