Earthworm Aporrectodea trapezoides had no effect on the dispersal of a vesicular-arbuscular mycorrhizal fungi, Glomus intraradices

Abstract

We investigated the interactions between earthworms and vesicular-arbuscular (VA) mycorrhizal fungi. The effects of earthworms (Aporrectodea trapezoides) at three densities, on the initiation of mycorrhizal colonization of roots of Trifolium subterraneum L. were examined in Experiment 1. An increasing density of earthworms was associated with a decrease in proportional colonization of the roots by mycorrhizal fungi, with a significant difference between the treatment with no earthworms and that with three earthworms per pot (equivalent to 500 earthworms m(-2)). Experiment 2 was established to examine the effect of earthworms on the lateral spread of VA mycorrhizal Fungi from localized inoculum through a sward of T. subterraneum. A reduction in colonization was again observed at 14 and 21 days (Experiment 2A) or 14 and 28 days (Experiment 2B) but was not evident at a later harvest. The effects of earthworms on the infectivity of an established fungal hyphal network was examined in Experiment 3. The mean proportional colonization was consistently lower in the earthworm treatment compared to the no-earthworm treatment, except in the 1-3-cm section of soil, but none of the differences was statistically significant. We obtained no evidence that earthworms increase the rate of spread of mycorrhizal fungi between plants. Our results indicate that earthworms reduce the infectivity of the soil, with respect to VA mycorrhizal colonization of roots. However, the reduction may only be transient. Possible mechanisms for this effect include grazing on or disturbance of the hyphal network in soil.