Dominant herbaceous plants contribute to the spatial heterogeneity of beech and riparian forest soils by influencing fungal and bacterial diversity

Understanding of factors that shape diversity patterns in forest ecosystems is a main challenge in forest ecology and management practices. Although herbaceous plants are known to contribute to the maintenance of the structure and function of temperate forests, their impact on fungal and bacterial communities in soils is largely unknown. Therefore, we conducted a comparative study of soil fungal and bacterial diversity in two Central European deciduous forests, focusing on plots with dominant herbaceous species of contrasting morphology, phenology, reproduction, and ecology, including Allium ursinum and Dentaria enneaphyllos in a beech forest, as well as Aegopodium podagraria and Ficaria verna in a riparian forest. Plots with a mixture of herbaceous species and without plant cover were also studied. In both forests, fungal communities showed the strongest association with spatial location, part of which was explained by between-site variability in soil chemistry and was also influenced by herbaceous vegetation. The community composition of saprotrophic fungi depended on the presence and type of herbaceous vegetation in both forests. In addition, herbaceous plants affected the composition of arbuscular mycorrhizal fungi community in the beech forest, while in the riparian forest they affected endophytes and plant pathogens. For bacteria, soil chemistry played the most important role. Our results showed that dominant herbaceous vegetation is one of the drivers shaping microbial community composition, contributing to spatial heterogeneity of forest sites. Given that herbaceous species, especially those forming monospecific patches, affect the soil biotic properties in temperate forests, they should be included in forest management practices.