Litter decomposition in most terrestrial ecosystems is controlled predominantly by moisture-dependent microorganisms. In arid ecosystems, plant litter cycling exceeds predicted rates based on precipitation amounts, suggesting additional factors are involved. Attempts to reveal these factors have focused on abiotic degradation, precipitation frequency, soil-litter mixing, and alternative moisture sources. The role of detritivorous macro-arthropods in this process received less attention, despite their high relative abundance in most desert ecosystems. In our Negev Desert field site, burrowing macro-detritivores (the desert isopod Hemilepistus reaumuri) account for a great fraction of litter removal from the soil surface, and the soil around their burrows is enriched with nutrients and microbial biomass. In this study we tested whether the translocation of litter from dry and unstable environment aboveground into the moister and stabler burrow can result in enhanced decomposition. We performed a field pulse-chase experiment, using 13C-labeled litter and measuring the labeled-litter-derived respired carbon. We used four treatments, placing litter (1) inside isopod burrows, (2) on top of isopod-feces mounds outside burrows, (3) on the soil surface as an aboveground control, and (4) inside an artificial burrow as a belowground control. Measurements were performed in discrete campaigns during 10 months, with increased frequency following rain events.
Results/Conclusions
In the dry summer we found only negligible decomposition both above- and belowground. After rain events we witnessed a pronounced rise in decomposition rates that faded quickly aboveground but much slower belowground, allowing continuous decomposition between rain pulses. Total litter mass loss was two-fold higher below- than aboveground and was significantly higher in isopod burrows in comparison to the artificial ones. Our findings suggest burrowing detritivores are substantial drivers of litter decomposition in desert ecosystems, redistributing litter to moist and stable environments, where decomposition is remarkably enhanced, subsequently elevating soil nutrient levels.