Biotic interactions outweigh abiotic factors as drivers of bark microbial communities in Central European forests

Abstract

Bark surfaces are extensive areas within forest ecosystems, that provide an ideal habitat for microbial communities, through their longevity and seasonal stability. Here we provide a comprehensive account of the bark surface microbiome of living trees in Central European forests, and identify drivers of diversity and community composition. We examine algal, fungal and bacterial communities and their interactions using metabarcoding on samples from over 750 trees collected in the Biodiversity Exploratories in northern, central and southern Germany. We show that mutual biotic influence is more important than the abiotic environment with regard to community composition, whereas abiotic conditions and geography are more important for alpha diversity. Important abiotic factors are the relative humidity and light availability, which decrease the algal and bacterial alpha diversity, but strongly increase fungal alpha diversity. In addition, temperature is important in shaping the microbial community, with higher temperature leading to homogeneous communities of dominant fungi, but high turnover in bacterial communities. Changes in the community dissimilarity of one organismal group occurs in close relation to changes in the other two, suggesting that there are close interactions between the three major groups of the bark surface microbial communities, which may be linked to beneficial exchange. To understand the functioning of the forest microbiome as a whole, we need to further investigate the functionality of interactions within the bark surface microbiome and combine these results with findings from other forest habitats such as soil or canopy.

Surveying lichen diversity in forests: A comparison of expert mapping and eDNA metabarcoding of bark surfaces

“…For example, species co-occurrences, based on eDNA, could be used to explore the concept of photobiont-mediated guilds (Rikkinen 2003). We have previously shown -based on the same DNA samples used here -that the communities of fungi, green algae and bacteria present on bark surfaces, strongly affect each other's beta diversities (Dreyling et al 2024), suggesting that functional guilds, for example, of mycobionts and their photobiont partners, might be also be detected in the present data. Taxonomic assignments need to be carefully examined to assess if assignments are sensible for the geographic region of interest.…”

Supplementary material 1 from: Dreyling L, Boch S, Lumbsch HT, Schmitt I (2024) Surveying lichen diversity in forests: A comparison of expert mapping and eDNA metabarcoding of bark surfaces. MycoKeys 106: 153-172. https://doi.org/10.3897/mycokeys.106.117540

“…For example, species co-occurrences, based on eDNA, could be used to explore the concept of photobiont-mediated guilds (Rikkinen 2003). We have previously shown -based on the same DNA samples used here -that the communities of fungi, green algae and bacteria present on bark surfaces, strongly affect each other's beta diversities (Dreyling et al 2024), suggesting that functional guilds, for example, of mycobionts and their photobiont partners, might be also be detected in the present data. Taxonomic assignments need to be carefully examined to assess if assignments are sensible for the geographic region of interest.…”

“…In this study, we analyse the utility of eDNA -obtained from bark surfaces of tree trunks at breast height -to assess the diversity of lichen communities in central European forests. In previous studies, we have generated datasets of entire fungal communities associated with bark surfaces, based on ITS metabarcoding (Dreyling et al 2022(Dreyling et al , 2024Hofmann et al 2023). Here, we use only the fraction of lichenised fungi from these datasets.…”

Figure 3 from: Dreyling L, Boch S, Lumbsch HT, Schmitt I (2024) Surveying lichen diversity in forests: A comparison of expert mapping and eDNA metabarcoding of bark surfaces. MycoKeys 106: 153-172. https://doi.org/10.3897/mycokeys.106.117540

“…In this study, we analyse the utility of eDNA -obtained from bark surfaces of tree trunks at breast height -to assess the diversity of lichen communities in central European forests. In previous studies, we have generated datasets of entire fungal communities associated with bark surfaces, based on ITS metabarcoding (Dreyling et al 2022(Dreyling et al , 2024Hofmann et al 2023). Here, we use only the fraction of lichenised fungi from these datasets.…”