Impacts of earthworms on nitrogen acquisition from leaf litter by arbuscular mycorrhizal ash and ectomycorrhizal beech trees

Abstract

Earthworms (EWs) and mycorrhizal fungi are key components of soil biota participating in N recycling from leaf litter. The extent to which their interactions impact leaf litter-derived N uptake by tree species colonized by different mycorrhizal types and the variation of these interactions with leaf litter quality is unknown. We used a greenhouse experiment to investigate the effects of EWs on plant acquisition of N from 15N enriched ash (Fraxinus excelsior) and beech (Fagus sylvatica) leaf litter. We employed arbuscular mycorrhizal (AM) ash and ectomycorrhizal (EM) beech trees. EW presence did not affect the overall root mycorrhizal colonization, but in the beech leaf litter treatment it caused a shift in the EM fungal community, favoring species with a ruderal life strategy at the expense of more specialized species able to degrade organic compounds. No differences in 15N capture were found between EM and AM plants. Generally, 2–7% of the N released from leaf litter was taken up by the plants. EWs uniformly increased plant acquisition of N from leaf litter. This effect was more pronounced in treatments with ash than in those with beech leaf litter, presumably because of higher degradability of ash than of beech litter. The results suggest that leaf litter quality dominates the impact of EWs on plant N acquisition from leaf litter while the mycorrhizal type is of minor importance.