Intraspecific trait shift reflects earthworm response to land-use intensification in peat grasslands

Peatland grasslands are ecologically valuable ecosystems that support biodiversity and provide key functions, such as carbon storage and water regulation. However, agricultural intensification can degrade these ecosystems by altering soil conditions and belowground communities. Earthworms, as important ecosystem engineers and prey for meadow birds, play a central role in soil processes and trophic interactions, yet their responses to land-use intensity in peat soils remain poorly understood. In this study, we examined how land management, soil physicochemical properties, and vegetation characteristics influence earthworm communities in 19 Dutch peat meadows. We assessed abundance, biomass, species richness, body size and species community composition in relation to land management variables and remote sensing indicators of land-use intensity (S2REP). Earthworm abundance and biomass increased with grass yield and S2REP, suggesting that more productive meadows support larger populations. Species richness, however, did not vary with land-use intensity. Average individual body size declined significantly under more intensive management, independent of juvenile proportions, indicating potential constraints on growth or condition. Communities were overall dominated by generalist, disturbance-tolerant species, while variation in species composition was more strongly linked to soil salinity than land-use intensity. Our findings show that land-use intensity primarily affects earthworm abundance and functional traits, particularly body size, rather than taxonomic diversity. These shifts may impact soil functioning and reduce the energetic value or accessibility of earthworms for meadow birds. Incorporating trait-based approaches alongside taxonomic assessments offers a more mechanistic understanding of how agricultural practices influence belowground biodiversity and ecosystem function in peatland grasslands. • Earthworm abundance and biomass increase with grass productivity in peat grassland. • Intraspecific body size declines as land-use intensity increases, independent of juvenile proportion or species composition. • Intraspecific trait shifts capture management effects more clearly than species richness. • S2REP provides a robust proxy for land-use intensity impacts on earthworm communities.