Data from: Tree litter functional diversity and nitrogen concentration enhance litter decomposition via changes in earthworm communities

Biodiversity is a major driver of numerous ecosystem functions. However,
consequences of changes in forest biodiversity remain difficult to predict
because of limited knowledge about how tree diversity influences ecosystem
functions. Litter decomposition is a key process affecting nutrient
cycling, productivity and carbon storage, and can be influenced by plant
biodiversity. Leaf litter species composition, environmental conditions,
and the detritivore community are main components of the decomposition
process, but their complex interactions are poorly understood. In this
study, we tested the effect of tree functional diversity (FD) on litter
decomposition in a field experiment manipulating tree diversity, and
partitioned the effects of litter physio-chemical diversity and the
detritivore community. We used litterbags with different mesh sizes to
separate the effects of microorganisms and microfauna, mesofauna, and
macrofauna, and monitored soil fauna using pitfall traps and earthworm
extractions. We hypothesized that higher tree litter FD accelerates litter
decomposition due to the availability of complementary food components and
higher activity of detritivores. Although we did not find direct effects
of tree FD on litter decomposition, we identified key litter traits and
macro-detritivores that explained part of the process. Litter mass loss
was found to decrease with an increase in leaf litter carbon:nitrogen
ratio. Moreover, litter mass loss increased with an increasing density of
epigeic earthworms, with most pronounced effects in litterbags with a
smaller mesh size, indicating indirect effects. Higher litter FD and
litter nutrient content were found to increase the density of surface
dwelling macrofauna and epigeic earthworm biomass. Based on structural
equation modeling, we conclude that tree FD has a weak positive effect on
soil surface litter decomposition by increasing the density of epigeic
earthworms, and that litter nitrogen-related traits play a central role in
tree composition effects on soil fauna and decomposition.