Persistent macrodetritivore functional diversity and identity effects on litter mass loss under drought in a Mediterranean forest understory model ecosystem

Abstract

Soil macrofauna's role in plant litter decomposition is increasingly recognized, with litterbag experiments in natural and lab settings highlighting its contribution in various pedoclimatic context. Recent findings indicate that macrofauna can counteract drought-induced slowing of decomposition and nutrient cycling, but the underlying mechanisms remain unclear. Characteristics of macrofauna communities, such as functional diversity (FD), community-weighted mean (CWM) traits, and species identity, may drive these effects and modulate decomposition responses to drought. In a controlled experiment simulating a Mediterranean forest understory, we tested how different macrodetritivore assemblages with increasing FD, based on five decomposition-related traits, affect decomposition under drought. We hypothesized that both FD and CWM of consumption rate would increase litter mass loss, with stronger effects under drought. Irrespective of species composition, results showed that higher FD significantly promoted litter mass loss, while consumption rate CWM had a small additional effect, supporting complementarity among species over the mass-ratio hypothesis. Species identity explained more variance than FD and CWM combined, highlighting the influence of specific species in the assemblages. Although drought reduced overall litter mass loss, the positive relationship between FD and mass loss persisted, suggesting that diverse macrodetritivore communities continue to promote decomposition and nutrient cycling under drought. This suggests that more functionally diverse macrodetritivore communities continue to promote litter decomposition and, consequently, nutrient cycling, even during periods of drought. These findings emphasize the importance of macrodetritivore communities in litter decomposition across climatic conditions and highlight the need to consider species identity in future biodiversity-ecosystem function studies.