Changes amid constancy: Flower and leaf microbiomes along land use gradients and between bioregions

Abstract

Microbial communities inhabiting above-ground parts of plants affect their host's development, fitness and function. Although studies on plant-associated microbes are of growing interest, environmental drivers of flower microbiomes in particular are poorly characterized. In this study, we investigated flower and leaf epiphytic bacterial microbiomes of Ranunculus acris and Trifolium pratense using metabarcoding of 16S ribosomal DNA in three German bioregions and along land-use intensity gradients. Our data suggests that the structures of bacterial communities clearly differed between plant species and tissue types. Also, floral bacterial communities of R. acris showed higher variability in comparison to T. pratense.Bacteria usually associated with pollinators were found solely in flower samples, while such usually associated with the rhizosphere were only present in high abundances on leaves. We identified Pseudomonadaceae, Enterobacteriaceae and Sphingomonadaceae as the most abundant taxa on flowers, while Sphingomonadaceae, Methylobacteriaceae and Cytophagaceae dominated bacterial communities on leaves. We found strong bacterial turnover already for short geographic distances, which however did not increase with the long distances between bioregions. High land use intensity caused phylogenetically less diverse and more homogenous bacterial communities. This was associated with a loss of rare bacterial families. Intensification of mowing and fertilization affected almost all plant associated bacterial communities, while grazing had only minor effects on bacterial structures of T. pratense flowers. However, dominant taxa were mostly resilient to mowing, grazing and fertilization. Despite that, we identified indicator taxa for regularly disturbed environments in flower microbiomes.

Do amino and fatty acid profiles of pollen provisions correlate with bacterial microbiomes in the mason beeOsmia bicornis?

“…Interestingly, this was also the case for pupae, where even after voiding the gut, a similar bacterial microbiome was still observable. For example, bacteria that are likely derived from flowers, such as Pseudomonas, Xanthomonas, Acinetobacter and Sphingomonas [41,43,93], contributed in large fractions to the overall community. Other bacteria that were reported for guts of different social and solitary bee species, e.g.…”

“…in megachilid bees [36]. In fact, different flowering plant species show distinct microbial communities [41,42] and the beta-diversity of floral microbiota is usually higher between flowers of different plant species than between flowers of the same plant species [43].…”

Manipulation of phyllosphere bacterial communities reversibly alters the plant microbiome and leaf traits in the field

“…We found that community composition of bacteria was shaped by plant communities of different ages along the succession, which in turn differed in their species composition. Plant species identity is widely considered the predominant factor influencing the composition of foliar bacteria, as plant genetic traits mediate production of secondary metabolites and topology of the leaves (Junker and Keller 2015;Boachon et al 2019;Gaube et al 2020). This is specifically the case for the so-called core plant microbiome, which consists of microorganisms that are selected by a certain plant species or genotype, largely independent of environmental conditions (Kumar et al 2017;Compant et al 2019).…”

“…The leaf surface, or phyllosphere, is inhabited by a diverse variety of microorganisms, predominantly bacteria (Stone et al 2018). Microbial community establishment on plants is not random but undergoes selection depending on host species identity, as well as on temporal and spatial effects (Laforest-Lapointe et al 2016;Gaube et al 2020). Leaf-associated microbiota can emerge from the surrounding environment or be transferred across generations of plants via seeds (Mitter et al 2017;Escobar Rodríguez et al 2020).…”

Are microbes growing on flowers evil? Effects of old flower microbes on fruit set in a wild ginger with one-day flowers, Alpinia japonica (Zingiberaceae)

“…It maintains humidity and nutrients necessary for pollen tube growth (Taylor and Hepler 1997), which would also be beneficial for microbes. Recent studies using high-throughput sequencing have revealed highly diverse microbial communities on flowers of many species in a wide range of habitats (Gaube et al 2021;Massoni et al 2020;Wei and Ashman 2018).…”