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

Abstract

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 physiochemical 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 macrodetritivores 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.

Leaf litter identity rather than diversity shapes microbial functions and microarthropod abundance in tropical montane rainforests

“…In contrast with C mic and M loss , the abundance of microarthropods was not affected by litter diversity (Table 3). Some previous studies found mixtures to promote the abundance of microarthropods (Hansen, 2000; Hättenschwiler & Gasser, 2005; Migge et al., 1998; Schädler & Brandl, 2005), while others did not find evidence that litter diversity beneficially affects microarthropods (Bluhm et al., 2019; Ilieva‐Makulec et al., 2006; Korboulewsky et al., 2016; Patoine et al., 2020; Scheu et al., 2003). Our results agree with the latter findings and support the results of Marian et al.…”

“…(2018) suggesting that litter diversity in this tropical rainforest neither improves habitat conditions nor the availability of resources for microarthropods, at least during early stages of decomposition. Indeed, detritivore microarthropods are considered to comprise predominantly generalist feeders colonizing a range of forest types and therefore are rather insensitive to changes caused by litter mixing (Ball et al., 2014; Gergócs & Hufnagel, 2016; Patoine et al., 2020; Wardle et al., 2006). However, even though litter diversity did not affect microarthropod abundance, it may still have fostered the diversity of microarthropods, as has been shown for other soil organisms, such as testate amoebae at our study site (Krashevska et al., 2017).…”

Soil Macrofauna Diversity and Litter Decomposition Rate in the Buffer Zone of Lore Lindu Biosphere Reserve Indonesia

“…In overall, the average similarity index during observations on the three sites is low, below 50% (21% to 35%). The behavior of macrofauna in food preferences during sufficient amount of litter is a factor causing the high similarity index at the beginning of the observation [42]. Meanwhile, the similarity index decreases in line with the decrease in the amount of litter.…”

Tree species mixing causes a shift in fine‐root soil exploitation strategies across European forests

“…Third, the spatial distribution of soil resources may also partly explain our observations. A weak but positive tree diversity effect on abundance and diversity of earthworms was observed across the FunDivEUROPE plots (De Wandeler et al, 2018), indicating an increased bioturbation and redistribution of soil nutrients in mixtures (Meysman et al, 2006;Patoine et al, 2020). As a response, trees could have formed higher-SRL roots to enhance their chance of encountering nutrient-rich spots .…”