Herbivore versus detritivore effect on decomposition through leaf conversion into faeces

In terrestrial ecosystems, plant residues can reach the soil as senesced leaf litter or green leaves, and both types can be transformed by invertebrates into detritivore or herbivore faeces. Yet, the consequences of this conversion on decomposition rates and soil fertility are largely unknown. To fill this knowledge gap, we collected faeces from caterpillars ( Historis odius ; herbivores) and millipedes ( Anadenobolus monilicornis ; detritivores), which were fed green and dead leaves of Cecropia schreberiana , respectively, in a tropical ecosystem context. We then incubated green leaves, herbivore faeces, dead leaves and detritivore faeces in a microcosm experiment for 180 days to measure their decomposition and underlying soil parameters. Our results showed significant effects of (1) leaf senescence, with green leaves decomposing faster than leaf litter, and of (2) leaf conversion to invertebrate faeces, with faeces decomposing faster than intact leaves for both herbivore and detritivore faeces. However, contrasting patterns emerged between carbon and nitrogen dynamics, as nitrogen cycling was generally slower for faeces than for litter, with a particularly notable reduction in nitrogen losses for herbivore faeces. Consequences for the biogeochemistry of the underlying soil, specifically soil mineral nitrogen, were also observed. This pioneering study on faeces decomposition in a tropical context suggests that leaf‐feeding invertebrates, whether herbivores or detritivores, accelerate decomposition processes by converting leaves into faeces. This consistent acceleration of decomposition could have important consequences for soil organic matter formation and nutrient returns to plants. Read the free Plain Language Summary for this article on the Journal blog.