Contrasting responses to aridity by different-sized decomposers cause similar decomposition rates across a precipitation gradient

Abstract

Litter decomposition is expected to be positively associated with precipitation despite evidence that decomposers of varying sizes have different moisture dependencies. We hypothesized that higher tolerance of macro-decomposers to aridity may counterbalance the effect of smaller decomposers, leading to similar decomposition rates across climatic gradients. We tested this hypothesis by placing plant litter baskets of different mesh sizes in seven sites along a sharp precipitation gradient, and by characterizing the macro-decomposer assemblages using pitfall trapping. We found that decomposers responded differently to precipitation levels based on their size, leading to similar overall decomposition rates across the gradient except in hyper-arid sites. Microbial decomposition was minimal during the summer, but in the winter was positively associated with precipitation, governing the whole-community decomposition. Meso-decomposition was moderate in both seasons and peaked in semi-arid sites. Macro-decomposition contributed minimally to whole-community decomposition during the winter, but during the summer dominated decomposition in the two arid sites. Macro-decomposer richness, abundance and biomass peaked in arid environments. Our findings highlight the importance of macro-decomposition in arid-lands, possibly resolving the dryland decomposition conundrum, and emphasizing the need to contemplate decomposer size when investigating zoogeochemical processes.

Climate dependence of the macrofaunal effect on litter decomposition—A global meta‐regression analysis

“…Our meta‐regression analyses suggest that macro‐decomposition in hot drylands may compensate for the limited moisture‐dependent decomposition by smaller organisms, leading to much higher overall decomposition rates than those expected based on current theory. These global findings correspond with evidence from local experiments showing that macro‐detritivores dominate plant litter decomposition, especially during hot and dry periods (Sagi et al., 2019, 2021; Torsekar et al., 2023). Consequently, our work provides a plausible resolution to the longstanding DDC, diverting the focus from abiotic factors to macro‐arthropods.…”

“…In these important biomes that cover 19% of the global land area (Cartereau et al., 2022), macrofauna increased litter mass loss on average by 145% (Figure 3). The effect of macrofauna on decomposition in arid sites is expected to be even higher, since subtropical deserts include hyper‐arid sites in which climate conditions are too extreme and resources are too scarce and unpredictable to sustain large macrofaunal populations and diverse detritivore assemblages (Torsekar et al., 2023). Similar to our findings, a global cross‐biome experiment that explored termites' effect on wood decomposition revealed the highest decomposition rates in subtropical deserts (Zanne et al., 2022).…”

“…than precipitation per se. In hyper-arid ecosystems, low and unpredictable primary productivity may limit the abundance of macro-detritivores (Torsekar et al, 2023). Hence, the macrofaunal effect in these systems is expected to be minimal (Figure 1b).…”

“…mean annual precipitation divided by potential evapotranspiration; Zomer et al., 2022) to be a better predictor of macro‐decomposition than precipitation per se. In hyper‐arid ecosystems, low and unpredictable primary productivity may limit the abundance of macro‐detritivores (Torsekar et al., 2023). Hence, the macrofaunal effect in these systems is expected to be minimal (Figure 1b).…”