Ground-lying deadwood volume promotes soil beta diversity but not alpha diversity in European temperate forests

Background and aims: Deadwood plays a vital role in forest ecosystems, influencing soil biodiversity through nutrient enrichment and niche partitioning. While the effects of specific attributes of deadwood logs on soil biodiversity are well studied, it remains unclear whether and how the volume of deadwood affects soil biodiversity at the scale of forest stands. Additionally, the effects on soil biodiversity may differ between gradually accumulated deadwood and large volumes resulting from sudden stand-level disturbance events. In this study, we aim to assess such effects on alpha and beta diversity of soil microbes and microfauna. Methods: Soil samples were gathered from forest plots following a gradient of deadwood volumes in European temperate forests in Germany and The Netherlands. Using extracellular DNA metabarcoding, we analysed the soil diversity of bacteria, fungi and microarthropods. For the Bavarian Forest National Park, we also compared the diversity patterns of these biotas between areas affected by bark beetle outbreaks and unaffected areas of Norway spruce forest. Results: Increased deadwood stock had a marginal effect on soil microbial and microarthropod community composition, with no impact on overall diversity. Bark beetle-affected areas had distinct soil communities, with a lower fungal and microarthropod diversity. Conclusion: Our study provides the first insights into soil diversity patterns associated with increased deadwood volume at the forest stand. While shifts in soil biodiversity composition were minimal, the retention of deadwood in European temperate forests can promote heterogeneity in soil communities. Furthermore, changes in soil biodiversity following bark beetle outbreaks may have long-term consequences on forest regeneration.