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 bacteria 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 that bacterial communities did not differ between long-distant regions. However, there was a turnover within each bioregion between short-distant locations. High land use intensity caused phylogenetically less diverse and more homogenous bacterial communities with an exception of T. pratense flowers. This was associated with a loss of rare bacterial families. Intensification of mowing affected the bacterial communities associated with leaves of T. pratense and fertilization led to more homogenous flower and leaf communities of R. acris, while grazing had no effects on the bacterial community composition. However, dominant taxa were not affected by land use intensification. Despite that, we identified indicator taxa for regularly disturbed environments in flower microbiomes. In conclusion, our study contributes to the knowledge about microbial community structures of the phyllosphere and extends the understanding of their community dynamics with respect to biogeographical separation and anthropogenic changes of the environment.

中文翻译：

---

恒定中的变化：沿土地利用梯度和生物区之间的花和叶微生物组

摘要 栖息在植物地上部分的微生物群落影响宿主的发育、健康和功能。尽管对植物相关微生物的研究越来越受到关注，但特别是花卉微生物组的环境驱动因素的特征却很差。在这项研究中，我们使用 16S 核糖体 DNA 在三个德国生物区和土地利用强度梯度的元条形码研究了毛茛和三叶草的花和叶附生细菌微生物组。我们的数据表明，细菌群落的结构在植物物种和组织类型之间明显不同。此外，与 T. pratense 相比，R. acris 的花细菌群落表现出更高的变异性。通常与传粉媒介有关的细菌仅在花样中发现，而通常与根际相关的细菌只在叶子上大量存在。我们确定假单胞菌科、肠杆菌科和鞘氨醇单胞菌科是花上最丰富的分类群，而鞘氨醇单胞菌科、甲基杆菌科和噬菌体科在叶子上占主导地位。我们发现远距离区域之间的细菌群落没有差异。然而，在短距离位置之间的每个生物区域内都有周转。高土地利用强度导致除 T. pratense 花外，系统发育多样性较少且细菌群落更加均一。这与稀有细菌家族的丧失有关。加强割草影响了与 T 叶相关的细菌群落。pratense 和施肥导致 R. acris 的花和叶群落更加均匀，而放牧对细菌群落组成没有影响。然而，优势类群不受土地利用集约化的影响。尽管如此，我们还是确定了花卉微生物群中经常受到干扰的环境的指示类群。总之，我们的研究有助于了解叶际微生物群落结构，并扩展对生物地理分离和环境人为变化方面的群落动态的理解。