Plant litter functional diversity effects on litter mass loss depend on the macro-detritivore community

Abstract

A better understanding of the mechanisms driving litter diversity effects on decomposition is needed to predict how biodiversity losses affect this crucial ecosystem process. In a microcosm study, we investigated the effects of litter functional diversity and two major groups of soil macro-detritivores on the mass loss of tree leaf litter mixtures. Furthermore, we tested the effects of litter trait community means and dissimilarity on litter mass loss for seven traits relevant to decomposition. We expected macro-detritivore effects on litter mass loss to be most pronounced in litter mixtures of high functional diversity. We used 24 leaf mixtures differing in functional diversity, which were composed of litter from four species from a pool of 16 common European tree species. Earthworms, isopods, or a combination of both were added to each litter combination for two months. Litter mass loss was significantly higher in the presence of earthworms than in that of isopods, whereas no synergistic effects of macro-detritivore mixtures were found. The effect of functional diversity of the litter material was highest in the presence of both macro-detritivore groups, supporting the notion that litter diversity effects are most pronounced in the presence of different detritivore species. Species-specific litter mass loss was explained by nutrient content, secondary compound concentration, and structural components. Moreover, dissimilarity in N concentrations increased litter mass loss, probably because detritivores having access to nutritionally diverse food sources. Furthermore, strong competition between the two macro-detritivores for soil surface litter resulted in a decrease of survival of both macro-detritivores. These results show that the effects of litter functional diversity on decomposition are contingent upon the macro-detritivore community and composition. We conclude that the temporal dynamics of litter trait diversity effects and their interaction with detritivore diversity are key to advancing our understanding of litter mass loss in nature.

Litter decomposition driven by soil fauna, plant diversity and soil management in urban gardens

“…A loss or change of decomposer diversity and species composition is likely to alter decomposition dynamics (Hättenschwiler and Gasser, 2005;Heemsbergen, 2004), but its extent and consequences remain difficult to predict (García-Palacios et al, 2016a;Hooper et al, 2005). The majority of studies has analysed the effect of different litter types on decomposition (Patoine et al, 2017) and has shown a mean positive effect of leaf litter species diversity on litter mass loss across biomes (Handa et al, 2014). Nielsen et al (2011) explored the relationship between soil fauna and ecosystem functions relevant for C cycling.…”

“…In 11 out of 15 studies, they reported a positive relationship between soil fauna species richness and decomposition. Yet, the role of soil fauna on litter decomposition, including not only taxonomic but also functional or phylogenetic metrics, remains mostly unknown (Patoine et al, 2017), especially in urban ecosystems (Schwarz et al, 2017), were environmental conditions and management practices can be profoundly different compared with rural areas (Gaston et al, 2010).…”

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

“…In addition to functional diversity effects, we expected the CWM and variance of certain functional traits to affect litter mass loss (Table 1) (hypothesis 3). For instance, as found in a microcosm study using the same litter mixtures (Patoine et al, 2017), more rapid decomposition was expected for mixtures characterized by high nutrient content, low concentration of defensive compounds (tannins and phenolics), and low leaf stability/strength (thickness and toughness). We expected the variance of nutrient-related traits (leaf N content, leaf C:N, litter C:N) to increase litter mass loss, as diverse mixtures would provide detritivores with complementary food sources to fulfill their nutritional needs (Vos, van Ruijven, Berg, Peeters, & Berendse, 2013).…”

“…Similarly, a few other studies also found that FD effects on litter decomposition in mixtures were not significant (Frainer, Moretti, Xu, & Gessner, 2015;Tardif & Shipley, 2015). Partly, inconsistent findings may be due to different litter traits being considered in previous studies as well as temporal dynamics in the decomposition process, and the varying role of litter traits during different stages of litter decomposition (Patoine et al, 2017;Ristok et al, 2017). To exemplify these interactions, a laboratory study that used the same litter mixtures as presented here (i.e., based on the BIOTREE-FD site design) found a positive effect of litter FD on decomposition, but only for a given time period of the experiment, with the effect disappearing at later stages of the experiment (Patoine et al, 2017).…”

“…We expected the exclusion of mesoand macrofauna to incrementally reduce litter mass loss in litterbags of smaller mesh sizes. We hypothesized that more functionally diverse litter mixtures would show faster decomposition, with a stronger effect with increasing mesh sizes as macro-decomposers have been shown to modulate litter diversity effects (Hättenschwiler & Jørgensen, 2010;Patoine et al, 2017) (hypothesis 1). Tree communities with higher functional diversity were expected to provide more diverse food sources and create more complex and heterogeneous environmental conditions that support a more abundant and diverse fauna community (Hooper, 2000), with detritivores in turn contributing to faster litter mass loss (hypothesis 2).…”