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.
Highlights
Dead wood decay is a key component of ecosystem functioning in forests (Harmon et al 1986, Cornwell et al 2009, Wirth et al 2009), most importantly of carbon sequestration and release as well as nutrient cycling (Chambers et al 2000, Wirth et al 2009)
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 operational taxonomic unit (OTU) richness and invertebrate diversity using piecewise structural equation models
Tree species diversity did not have a positive effect on wood decay rates which was driven by the microclimate
Summary
Dead wood decay is a key component of ecosystem functioning in forests (Harmon et al 1986, Cornwell et al 2009, Wirth et al 2009), most importantly of carbon sequestration and release as well as nutrient cycling (Chambers et al 2000, Wirth et al 2009). A growing body of literature reports positive effects of forest biodiversity on various ecosystem functions (reviewed by Nadrowski et al 2010, Duffy et al 2017). Decomposition dynamics of dead wood have, so far, been widely neglected in forest biodiversity–ecosystem functioning (BEF) experiments. To our knowledge only two studies have recently tested effects of tree species and decomposer diversity on dead wood dynamics (Eichenberg et al 2017, Kahl et al 2017). It remains largely unknown whether and how dead wood decomposition is affected by changes in biodiversity beyond the well described effect of abiotic conditions. We explored three modes of tree species diversity effects: via a modification of the microclimate for decomposition, via altering decomposer diversities, and via direct effects of unknown mechanism
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