Burrowing detritivores regulate nutrient cycling in a desert ecosystem

Nutrient cycling in most terrestrial ecosystems is thought to be controlled by moisture-dependent decomposer activity. In arid ecosystems, plant litter cycling exceeds rates predicted based on precipitation amounts, suggesting that additional factors are involved in these systems. Attempts to reveal these factors have predominantly focused on abiotic degradation, precipitation frequency, soil-litter mixing, and alternative moisture sources. Our aim was to explore an additional hypothesis that macro-detritivores control litter cycling in deserts. We quantified the role different organisms play in clearing plant detritus from the desert surface, using litter-baskets with different mesh sizes that allow selective entry of micro-, meso- or macro-fauna. We also measured soil nutrient concentrations in increasing distances from the burrows of a highly abundant macro-detritivore, the desert isopod Hemilepistus reaumuri, in the field and in laboratory microcosms. Macro-detritivores controlled the clearing of plant litter in our field site. The highest rates of litter removal were measured during the hot and dry summer when isopod activity peaks and microbial activity is minimal. We also found substantial enrichment of inorganic nitrogen and phosphorous in the vicinity of isopod burrows. We conclude that burrowing macro-detritivores are important regulators of litter cycling in this arid ecosystem, providing a plausible general mechanism that explains the unexpectedly high rates of plant-litter cycling in deserts.