Plant diversity changes the trophic position of Collembola in temperate grassland

Biodiversity loss threatens ecosystem functions, including decomposition and nutrient cycling. We investigated whether Collembola (springtails), key soil decomposers, adjust their trophic positions in response to plant diversity in a long-term temperate grassland experiment (the Jena Experiment). Using stable isotope analysis ( 13 C, 15 N), we examined trophic positions of five Collembola families across a gradient of plant species richness and plant- and soil-history treatments. In June 2021, Collembola and plant material were sampled across 240 plots. Collembola families spanned about one trophic level, forming part of the first two trophic levels of the soil food web with relatively narrow basal resource use. Our results demonstrate that Collembola trophic niches were significantly affected by soil history and legume presence. Plant diversity had a weak effect on Collembola trophic niches. Notably, the trophic position of Onychiuroidea increased from monocultures to 60 species plots by about one trophic level in new soil, suggesting a dietary shift from root feeding to microbial consumption. By contrast, the trophic position of Isotomidae decreased by about 1/3 trophic level, likely reflecting a shift towards more detrital food. Overall, the trophic level (Δ 15 N values) of Collembola was more strongly affected than their use of basal resources (Δ 13 C values). Importantly, this study is the first to document how Collembola shift trophic roles due to changes in plant diversity and soil history — offering new insights into soil food web dynamics. The findings highlight trophic flexibility of belowground detritivores, with implications for ecosystem functioning under biodiversity loss and land-use change.