Soil fauna communities are major drivers of many forest ecosystem processes. Tree species diversity and composition shape soil fauna communities, but their relationships are poorly understood, notably whether or not soil fauna diversity depends on tree species diversity. Here, we characterized soil macrofauna communities from forests composed of either one or three tree species, located in four different climate zones and growing on different soil types. Using multivariate analysis and model averaging we investigated the relative importance of tree species richness, tree functional type (deciduous vs. evergreen), litter quality, microhabitat and microclimatic characteristics as drivers of soil macrofauna community composition and structure. We found that macrofauna communities in mixed forest stands were represented by a higher number of broad taxonomic groups that were more diverse and more evenly represented. We also observed a switch from earthworm-dominated to predator-dominated communities with increasing evergreen proportion in forest stands, which we interpreted as a result of a lower litter quality and a higher forest floor mass. Finally, canopy openness was positively related to detritivore abundance and biomass, leading to higher predator species richness and diversity probably through trophic cascade effects. Interestingly, considering different levels of taxonomic resolution in the analyses highlighted different facets of macrofauna response to tree species richness, likely a result of both different ecological niche range and methodological constraints. Overall, our study supports the positive effects of tree species richness on macrofauna diversity and abundance through multiple changes in resource quality and availability, microhabitat, and microclimate modifications. Keywords Community ecology • Forest ecosystems • Biodiversity-ecosystem functioning • Aboveground-belowground linkagesCommunicated by Stefan Scheu .
Earthworms can stimulate plant productivity, but their impact on soil greenhouse gases (GHG) is still debated. Methodological challenges of measuring GHG in experiments with plants are presumably contributing to the status quo, with the majority of studies being conducted without plants. Here we report the effect of earthworms (without, anecic, endogeic and their combination) and plants (with and without) on GHG (CO2 and N2O) emissions in an experiment. N2O emissions were also 34.6 and 44.8% lower when both earthworm species and only endogeic species were present, respectively, while plants reduced the cumulative N2O emissions by 19.8%. No effects on CO2 were found. Estimates of soil macroporosity measured by X-ray tomography show that the GHG emissions were mediated by their burrowing activity affecting the soil aeration and water status. Both GHG emissions decreased with the macropore volume in the top soil, presumably due to reduced moisture and microbial activity. N2O emissions also decreased with macropore volume in the deepest layer, likely caused by a reduction in anaerobic microsites. Our results indicate that, under experimental conditions allowing for plant and earthworm engineering effects on soil moisture, earthworms do not increase GHG emissions and that endogeic earthworms may even reduce N2O emissions.
<p>Accelerating climate change and biodiversity loss calls for agricultural practices that can sustain productivity with lower greenhouse gas emissions while maintaining biodiversity. Biodiversity-friendly agricultural practices have been shown to increase earthworm populations, but according to a recent meta-analyses, earthworms could increase soil CO<sub>2</sub> and N<sub>2</sub>O emissions by 33 and 42%, respectively. However, to date, many studies reported idiosyncratic and inconsistent effects of earthworms on greenhouse gases, indicating that the underlying mechanisms are not fully understood. Here we report the effects of earthworms (anecic, endogeic and their combination) with or without plants on CO<sub>2</sub> and N<sub>2</sub>O emissions in the presence of soil-moisture fluctuations from a mesocosms experiment. The experimental set-up was explicitly designed to account for the engineering effect of earthworms (i.e. burrowing) and investigate the consequences on soil macroporosity, soil water dynamic, and microbial activity. We found that plants reduced N<sub>2</sub>O emissions by 19.80% and that relative to the no earthworm control, the cumulative N<sub>2</sub>O emissions were 17.04, 34.59 and 44.81% lower in the anecic, both species and endogeic species, respectively. CO<sub>2</sub> emissions were not significantly affected by the plants or earthworms but depended on the interaction between earthworms and soil water content, an interaction that was also observed for the N<sub>2</sub>O emissions. Soil porosity variables measured by X-ray tomography suggest that the earthworm effects on CO<sub>2</sub> and N<sub>2</sub>O emissions were mediated by the burrowing patterns affecting the soil aeration and water status. N<sub>2</sub>O emissions decreased with the volume occupied by macropores in the deeper soil layer, whereas CO<sub>2</sub> emissions decreased with the macropore volume in the top soil layer. This study suggests that experimental setups without plants and in containers where the earthworm soil engineering effects via burrowing and casting on soil water status are minimized may be responsible, at least in part, for the reported positive earthworm effects on greenhouse gases.</p>
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