Leaf litter chemistry contributes to shape the chemical footprint of macrodetritivore communities

Addressing the factors underlying community patterns is a crucial endeavor as it contributes to a better understanding of the relationship between biodiversity and ecosystem functioning, as well as the associated ecosystem services. For example, detritivore communities play a major role in decomposition processes and related matter and energy fluxes in ecosystems. However, compared to living plant resources, leaf litter resources are nutritionally poor, with low macroelement concentrations. Although detritivore communities are known to depend on the local leaf litter resources, it remains unclear whether the chemical composition of detritivores depends on the locally available leaf litter. The macroelement composition of detritivores is rarely studied and is seldom compared directly to leaf litter chemical quality. Furthermore, leaf litter elements other than carbon (C), nitrogen (N), and phosphorus (P) are not systematically investigated even though large differences in elements such as calcium (Ca), potassium (K), or magnesium (Mg) can occur among both detritivore taxa and leaf litter types. To investigate whether the chemical composition of macrodetritivore communities depends on leaf litter chemistry, we sampled 24 paired French forests sites that differed in their leaf litter chemical composition. At each site, we quantitatively sampled leaf litter transformers (Diplopoda and Isopoda) to estimate their abundance. For each morphospecies, we measured mean individual body mass and analyzed body concentrations of C, N, P, K, Ca, and Mg (hereafter called chemical traits). We also analyzed the same macroelements in the dominant leaf litter at each site. We examined the detritivore taxonomic diversity, chemical community diversity, biomass, and abundance in communities, and tested whether these parameters were influenced by leaf litter chemistry. Results at the morphospecies level were consistent with the homeostasis hypothesis, indicating no specific physiological adaptation to the chemical composition of their trophic resources. Chemical community diversity (i.e., the FDis index based on all six chemical elements) of detritivores was higher at sites with high-quality leaf litter than at the corresponding low-quality leaf litter sites. Furthermore, community-level concentrations of P and Mg in detritivores were positively influenced by litter P and Mg concentrations, respectively. Although effect sizes were limited, our results suggest that leaf litter chemical composition can influence detritivore chemical composition through shifts in the relative abundance of taxa. Ultimately, this may lead to a closer match between the chemical composition of detritivore communities and that of their resources.