Variability in responses of soil nematodes to trace element contamination.

Free-living soil nematodes and plant parasites were previously repeatedly tested for their use as bioindicators of soil contamination. We investigated soil nematode communities from grasslands in four different industrial areas in Slovakia to estimate their responses to heavy metals. We considered differences or similarities in behavioural reactions of nematodes to different quantities of selected heavy metals in the soil. Using the CCA analysis and t-value biplot diagrams with van Dobben circles, we split individual nematode genera by their tolerance/intolerance to the particular heavy metal into several clusters. Our results showed that (a) representatives of nematode genera showed concurrently positive and negative associations with two or more heavy metals, (b) most nematode genera expressed a strong positive relation with Ni and to a lesser extend with Cr and Zn, (c) taxonomically closely related nematodes did not demonstrated similar responses to the same pollutant. We assume that nematode genera with a higher level of tolerance to trace elements should be prioritized in the heavy metal bioindication instead of sensitive species, due to their longer persistence in the stressed environment and better indicative ability. We pointed nematode genera, which according to received results may serve as suitable sentinels for specific soil pollutants.