Translocation of mycorrhizal fungi by earthworms during early succession

Abstract

The distribution of propagules of vesicular-arbuscular mycorrhizal (VAM) fungi by earthworms was investigated in a number of natural plant communities, differing in successional age. Propagule numbers were quantified using direct spore counts and the Most Probable Number (MPN) dilution method. Propagule number was low in early successional sites and was progressively higher in sites of 3yr and over. Results of spore counts and MPN analysis showed similar patterns. In all sites, earthworm cast material contained higher numbers of spores and infective propagules than nearby field soil. These differences were significant in sites of 5 yr and over. There was a positive relationship between MPN of propagules and spore counts in cast material, but spore counts underestimated total propagule numbers. It is suggested that, due to feeding on senescing roots, earthworms concentrate mycorrhizal propagules in their cast soil. Due to the fact that surface worm casts were more abundant in early succession, the deposition of propagules was comparable to that in older communities. Earthworms may therefore be important agents in the distribution of mycorrhizal fungi, and thereby influence plant establishment in early succession.