Parasitic trophic mode of plant host affects the extent of colonization, but does not induce systematic shifts in the composition of foliar endophytic assemblages in temperate meadow ecosystems

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. 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. 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. 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 harboured 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. A free Plain Language Summary can be found within the Supporting Information of this article.

Automated summary

Foliar endophytic bacteria and fungi in parasitic and non-parasitic plants were found to be diverse, dominated by generalist taxa, but highly similar across all studied species. Despite contrasting leaf tissue chemistry, the trophic mode of parasitic plants did not systematically affect the diversity, composition, or predicted biogeochemical function of the endophytic microbiomes under field conditions. Parasitic plants may possess mechanisms to regulate the extent of colonization by endophytic fungi.