1. Foliar endophytic bacteria and fungi are increasingly being recognized as important drivers of plant host phenotype – affecting a wide range of eco-physiological processes. However, we are still lacking fundamental ecosystem-level knowledge about the structure, function, and inter-species interactions in endophytic assemblages associated with plant hosts sharing a common life strategy or ecological specialization.

2. In this study, we chose two groups of plants with contrasting physiology as model systems: parasites and their hosts. We assessed whether plant life history strategy, namely differences in nutrient acquisition and accumulation, plays a role in structuring above-ground microbiomes under field conditions.

3. We focused on the structure, colonization extent, and potential function of foliar endophytic bacteria and fungi in three root hemiparasitic species (Orobanchaceae), one stem holoparasite (Convolvulaceae), and their potential host plants co-occurring in species-rich temperate grassland ecosystems. For this purpose, we combined next generation amplicon sequencing with quantitative real-time PCR, chemical analyses of leaf tissue, and, in the case of bacteria, functional predictions using information deposited in available databases.

4. We found the foliar endophytic assemblages to be diverse, dominated by generalist taxa, but highly similar across all studied species. Despite of the highly contrasting leaf tissue chemistry in the parasitic and non-parasitic plant species, the parasitic trophic mode did not induce systematic shifts in the diversity, composition, or predicted biogeochemical function of the endophytic microbiomes under field conditions. However, compared to their potential hosts, leaves of both hemiparasitic and holoparasitic species harbored significantly lower fungal counts, estimated as ß-actin gene copies ng DNA^-1, which suggests that parasitic plants may possess mechanisms to regulate the extent of colonization by endophytic fungi.

We have collected the leaves of (shoots in one case) of 12 different plant species from 10 different families, growing at 8 distinct locations, mostly in six replicates. These included three hemiparasitic plant species and one holoparasitic plant, along with their non-parasitic potential hosts.

Leaves were surface sterilized, homogenized, DNA extracted, bacterial and fungal DNA amplified by PCR, and amplicons sequenced on the Illumina platform. Bacterial and fungal presence was quantified by qPCR. Aliquotes of the leaf material were used for detailed analyses of tissue chemistry using ICP-MS.

There are missing tissue chemistry values in samples from 2 locations, not enough material was left due to diffuculty in extracting enough DNA and the neccessity to repeat the extractions, which used up most of the sample. These samples are clearly marked in the tables.