Does the substrate on which cryptogams grow matter for limno-terrestrial meiofauna?

Yelyzaveta Matsko, Bartłomiej Surmacz , Yevgen Kiosya, Daniel Stec

Cryptogam habitats support a wide range of limno-terrestrial meiofauna, but the factors that shape their communities are still not well understood. The physical substrate that cryptogams grow on (e.g., soil, the base of a tree, or its trunk) can influence local moisture, temperature, and nutrient conditions, yet its role in structuring meiofaunal assemblages has rarely been tested systematically. We examined this question in montane forests of the Ukrainian Carpathians, using DNA metabarcoding to compare the diversity and composition of tardigrade and rotifer communities across substrates. We expected that rotifers, with shorter life cycles and often higher population densities, would respond more strongly to environmental differences among substrates, whereas tardigrades would be less affected and more influenced by chance colonization. Our results supported these expectations. Rotifer richness and community composition varied across substrates, while tardigrade assemblages showed weaker and more variable responses. Analysis of phylogenetic diversity indicated phylogenetic clustering in rotifers, suggesting that closely related species have similar ecological preferences. Despite these contrasts, both groups showed signs of largely stochastic community assembly, with species turnover dominating differences among samples. Overall, our findings suggest that meiofaunal communities in cryptogam-associated habitats are shaped mainly by random colonization events, modulated by subtle and taxon-specific effects of microhabitat structure and vertical positioning.