Species Composition of Indigenous Trichoderma Fungi Affected by Cd, Ni and Zn Heavy Metals in Calcareous Chernozem Soil

Cadmium, nickel or zinc contaminated soils originating from a long-term heavy metal field experiment were used to assess the influence of those particular treatments on the coexistence of various Trichoderma species. The abundance of six indigenous Trichoderma spp. - T . atroviride , T . harzianum , T . pubescens , T . tomentosum , T . virens and T . viride - were studied 12 years after the application of Cd, Zn and Ni salts on four levels (0, 30, 90 and 270 mg·kg ⁻¹) in a calcareous chernozem soil. Trichoderma fungal colonies from the soil particles were estimated on selective media. The isolated strains were taxonomically characterized by microscopic visualization. A reduced Trichoderma fungal colonization was found at the lower ratio of the studied metals. No colonization could be recorded in the case of Cd, and a slightly increased abundance at Ni and Zn metal salts at the highest 270 mg·kg ⁻¹ doses. The species composition of the fungi varied considerably in the contaminated samples as a function of the metals and the applied doses. Correlation analysis revealed that the population density of T . atroviride , T . harzianum , T . pubescens , T . viride was negatively affected by the available Cd concentration. The nickel content of the soil, however, correlated positively with the abundance of T . harzianum (r = 0.955) and T . virens (r = 0.964). In addition to this finding, the frequency of T . viride and T . tomentosum showed significant positive and negative correlation with the Zn treatment (r = 0.955; r = -0.965, respectively). Great differences between the correlation and partial correlation coefficients suggested that the heavy metals may alter not only the abundance of the fungi, but the interspecific relationships among the indigenous Trichoderma population, as well. This fact is considered to have further influence on some other biotic parameters and the soil functioning in heavy-metal-affected soils.