Synergistic interactions between detritivores disappear under reduced rainfall

Abstract

Understanding the consequences of altered rainfall patterns on litter decomposition is critical to predicting the feedback effect of climate change on atmospheric CO 2 concentrations. While their effect on microbial decomposition received considerable attention, their effect on litter fragmentation by detritivores, the other dominant decomposition pathway, remains largely unexplored. Particularly, it remains unclear how different detritivore species and their interactions respond to changes in rainfall quantity and frequency. To fill this knowledge gap, we determined the contribution to litter decomposition of two detritivore species (millipede and isopod), separately and in combination, under contrasting rainfall quantity and frequency in a temperate forest. Although halving rainfall quantity and frequency decreased top-soil moisture by 7.8 and 13.1%, respectively, neither millipede-nor isopod-driven decomposition were affected by these changes. In contrast, decomposition driven by both detritivore species in combination was 65.5% higher than expected based on monospecific treatments under high rainfall quantity, but unchanged or even lower under low rainfall quantity. This indicates that while detritivore activity is relatively insensitive to changes in rainfall patterns, large synergistic interactions between detritivore species may disappear under future rainfall patterns. Incorporating interspecific interactions between decomposers thus seems critical to evaluate the sensitivity of decomposition to altered rainfall patterns.

Drivers of litter mass loss and faunal composition of detritus patches change over time

“…Thus, the effects of interactions of a diverse fauna are context-specific: in a laboratory experiment, synergistic interactions of earthworms and isopods promoted the decomposition of high-(alder) but not low-quality (oak) litter (Zimmer et al, 2005). Similarly, millipedes and isopods interacted synergistically and jointly increased decomposition rates under natural rainfall conditions, but this joint effect diminished when rainfall quantity was reduced (Joly et al, 2021). Hence, both habitat conditions and litter quality should be taken into account when predicting decomposition rates based on faunal composition or diversity.…”