Environmentally-driven dissimilarity of trait-based indices of nematodes under different agricultural management and soil types

Trait-based indices have been widely applied to determine the below-ground effects of anthropogenic disturbances on the nematofauna. Given that the aggregation of the nematode community into one index value might result in difficulties in the interpretation of the signal, we investigated whether trait-based indices of nematodes are sensitive enough to assess the soil quality in agricultural soil systems. In the case of 137 locations in the Netherlands, we compared the suitability of indices to assess soil microbial and (a)biotic conditions for six combinations of management and soil type. Nematode abundance was strongly correlated with soil phosphorus (explained variances: 43.8% for molar N:P ratio and 30.9% for C:P ratio) and less with microbial biomass (explained variance 26.0%). Generally, the nematode abundance reflected more the variances of abiotics and microbial parameters than trait-based indices did. Nematode maturity indices point to differences in management intensity between ecosystems, although maturity indices explained only a small fraction of the variance of soil parameters. For combinations of soil and management types, contrasting correlations between nematological indices and soil conditions were often detected. Agricultural soils can be seen as characterized by a disturbance continuum and observed correlations were low as soon as soil and ecosystem types were analyzed together. Still, the gradients in soil abiotics and microbial parameters were rather large in comparison to single combinations of soil and ecosystem type. Dissimilarities indicate that small gradients within comparable ecosystems can largely hamper the interpretation of some indices and hence applying trait-based indices to few locations in an attempt to assess the biological qualities at local scales should be performed with caution.