Drought and litter quality effects on the contribution of soil fauna to decomposition in a Mediterranean forest

Soil animals accelerate leaf litter decomposition and nutrient mobilization; however, the combined effects of drought and litter quality on their contributions to these key ecosystem processes remain underexplored. We investigated the effects of experimental drought and litter quality on soil fauna communities’ contributions to leaf litter decomposition in a Mediterranean forest. Leaf litter from Quercus ilex and Phillyrea latifolia, was incubated for one year in litterbags with varying mesh sizes across eight 150-m² plots; half received long-term drought treatment. We measured litter biomass loss in each litterbag, leaf litterfall, nitrogen concentrations in leaves and litter, photosynthetically active radiation at each plot. Soil mesofauna were sampled three times during litterbag incubation. Our results showed that litter mass loss was greater for P. latifolia under experimental drought, while no significant differences were found in controlled conditions. Soil animals generally preferred P. latifolia over Q. ilex in both treatments, although overall contribution to litter decomposition was slightly lower under drought. Light extinction rate was lower in drought plots with reduced canopy height, indicating potential degradation of lignin and cellulose by solar radiation. Litter of P. latifolia contained higher nitrogen concentrations than Q. ilex, attributed to its lower resorption efficiency, possibly explaining its preference by soil fauna detritivores. Drought significantly impacted soil mesofauna abundance, reducing their density by 37.9 %. Our research indicates that direct impacts of drought on soil fauna communities might constrain their ability to facilitate litter decomposition, hindering their capacity to counteract nutrient cycling slowdown in Mediterranean ecosystems amid ongoing climate change.