Negative effects of earthworms on soil nematodes are dependent on earthworm density, ecological category and experimental conditions

Abstract

Earthworms are ecosystem engineers and are able to induce considerable changes in soil. These modifications go beyond physical and chemical aspects, as earthworms also act as regulators of communities of microorganisms and invertebrates. Although several studies have sought to clarify the effects of earthworms on soil nematode communities, the observed effects are highly variable, and there is no consensus on these interactions. In this work, fifteen studies representing 187 observations evaluating the impact of earthworms on soil nematode communities were synthesized in a meta-analysis. Our results showed that earthworms reduced soil nematode abundance by 27%. Nevertheless, this effect depends on the ecological category of earthworm and their densities, as well as experimental conditions. Anecic earthworms exhibited a greater capacity for modifying soil nematode communities than other ecological categories of earthworms. High earthworm densities also had stronger effects on soil nematodes than lower densities (<100 ind. m−2). However, we found that the presence of plants in experiments cancels out the negative effects of earthworms on soil nematodes, suggesting that earthworms did not affect nematode densities in these environments.