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Abstract

While the number of studies on the role of biodiversity on ecosystem functioning is
steadily increasing, a key component of biogeochemical cycling in forests, dead wood
decay, has been largely neglected. It remains widely unknown whether and how dead
wood decay is affected by diversity loss in forests. We studied the hierarchical effects
of tree species diversity on wood decay rates in a subtropical forest landscape in southeast
China via its influence on fungal OTU richness and invertebrate diversity using
piecewise structural equation models. The experiment was conducted in natural forest
plots that span a wide gradient of tree species diversity embedded in a heterogeneous
topography. To account for interactions between macro-invertebrates and fungi, that
potentially modify the influence of tree biodiversity and climate on dead wood decay,
we compared a macro-invertebrate exclusion treatment with a control treatment that
allowed access to all types of decomposers.
Diversity effects of trees on wood decay rates were mostly negative and mediated
by the diversity of macro-invertebrates. However, the effects of tree species diversity
or fungal OTU richness and macro-invertebrate diversity on wood decay rates were
comparatively weak. Temperature affected decay rates positively and had the strongest
influence in all treatments. While the exclusion of macro-invertebrates did not lead
to a reduction of wood decay rates, our results suggest that they may however have a
mediating role in the process. In the presence of invertebrates the predictability of wood
decay rates was higher and we observed a tendency of a stronger temperature control.
Our results suggest that there is evidence for diversity effects on wood decomposition,
but the temperature control is still more important. Thus, an increase in
mean annual temperature will increase carbon and nutrient turnover through wood
decomposition in subtropical forest irrespective of biotic composition.