Nutrient scarcity strengthens soil fauna control over leaf litter decomposition in tropical rainforests

Abstract

Soil fauna is a key control of the decomposition rate of leaf litter, yet its interactions with litter quality and the soil environment remain elusive. We conducted a litter decomposition experiment across different topographic levels within the landscape replicated in two rainforest sites providing natural gradients in soil fertility to test the hypothesis that low nutrient availability in litter and soil increases the strength of fauna control over litter decomposition. We crossed these data with a large dataset of 44 variables characterizing the biotic and abiotic microenvironment of each sampling point and found that microbe-driven carbon (C) and nitrogen (N) losses from leaf litter were 10.1 and 17.9% lower, respectively, in the nutrient-poorest site, but this among-site difference was equalized when meso- and macrofauna had access to the litterbags. Further, on average, soil fauna enhanced the rate of litter decomposition by 22.6%, and this contribution consistently increased as nutrient availability in the microenvironment declined. Our results indicate that nutrient scarcity increases the importance of soil fauna on C and N cycling in tropical rainforests. Further, soil fauna is able to equalize differences in microbial decomposition potential, thus buffering to a remarkable extent nutrient shortages at an ecosystem level.

Fine roots stimulate nutrient release during early stages of leaf litter decomposition in a Central Amazon rainforest

“…However, in contrast to our hypothesis and earlier observations by Cuevas and Medina (1988), in our experiment, fine roots did not affect total litter mass, nor C and N loss, but reduced the lignin fraction in the remaining litter, which may have led to an accelerated mass loss in later stages of decomposition. Excluding fine roots may have excluded soil meso-and likely some soil microfauna (Powers et al 2009;Peguero et al 2019), however, we did not find a significant impact on litter mass loss. Moreover, the lack of differences in mass loss rates suggests that the size of the litterbags did not influence the results.…”

“…In tropical forests, litter decay and nutrient mineralization rates are generally fast due to hot and humid conditions, and are instead predominantly controlled by faunal litter fragmentation, litter stoichiometry and microbial decomposer activity (Cusack et al 2009;Powers et al 2009;Prescott 2010;Peguero et al 2019). The biochemical depolymerization of complex molecules (e.g., cellulose, lignin, chitin or proteins) to smaller units available for uptake by plants and microbes is catalyzed by a range of extracellular enzymes (Sinsabaugh et al 2002;Schimel and Bennett 2004).…”

Litter decomposition by soil fauna: effect of land use in agroecosystems

“…After the production of biomass the next important process is decomposition ( Wilkinson 1998 ). Litter decomposition mainly depends on the complex relationships between different groups of soil fauna and microorganisms that inhabit agroecosystems as well as climate and litter quality ( Swift et al., 1979 ; Peguero et al., 2019 ). Soil fauna plays a key role in organic matter decomposition ( Brussaard 1997 ; Smith and Bradford 2003 ; Lavelle et al., 2006 ).…”

Teatime in the Serengeti: macrodetritivores sustain recalcitrant plant litter decomposition across human-modified tropical savannahs

“…When accessible to macrodetritivores recalcitrant litter mass loss could equal or exceed labile litter mass loss. A number of species of millipedes, termites and woodlice have been shown to exhibit a preference for recalcitrant or nutrient poor litter qualities over labile litter (Hättenschwiler and Gasser 2005;Peguero et al 2019;Sitters et al 2014). As mentioned earlier, termites avoid readily digestible litterhigh sugar or labile fractionsdue to the fermentation process in termite guts (Abe et al 2000).…”

“…Several macrodetritivores, e.g. millipedes, termites and woodlice, prefer recalcitrant litter types (Hättenschwiler and Gasser 2005;Peguero et al 2019;Sitters et al 2014). For example, termite species ferment litter within the gut through a mutualistic relationship with microorganisms (i.e.…”