Low root functional dispersion enhances functionality of plant growth by influencing bacteria activities in European forest soils

Current studies show that multispecies forests are beneficial regarding biodiversity and ecosystem functionality. However, there are only little efforts to understand the ecological mechanisms behind these advantages of multispecies forests. Bacteria are among the key plant growth‐promoting microorganisms that support tree growth and fitness. Thus, we investigated links between bacterial communities, their functionality and root trait dispersion within four major European forest types comprising multispecies and monospecific plots. Bacterial diversity revealed no major changes across the root functional dispersion gradient. In contrast, predicted gene profiles linked to plant growth activities suggest an increasing bacterial functionality from monospecific to multispecies forest. In multispecies forest plots, the bacterial functionality linked to plant growth activities declined with the increasing functional dispersion of the roots. Our findings indicate that enriched abundant bacterial OTUs are decoupled from bacterial functionality. We also found direct effects of tree species identity on bacterial community composition, but no significant relations with root functional dispersion. Additionally, bacterial network analyses indicated that multispecies forest have a higher complexity in their bacterial communities, which points towards more stable forest systems with greater functionality. We identified a potential of root dispersion to facilitate bacterial interactions and consequently, plant growth activities.