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

Bacterial communities in the phyllosphere are shaped by host genotype and phenotype and spatio-temporal variation of the environment. In turn, bacteria have the potential for altering the plant phenotype. Field experiments can help to estimate bacterial effects on plant functional traits under natural conditions. We used a transplantation approach of culturable bacterial communities to explore how manipulation of leaf-associated microbial communities in two different successional stages within a glacier foreland can influence microbial composition and functional plant traits. Our study documents successional stage-specific variations in the composition of foliar bacterial communities and shifts therein throughout a season and between years. We show that cultured bacteria transferred between plant communities can alter diversity and composition of the microbiome on plant community level as well as species-specific functional plant traits of two selected plant species within one growing season. Furthermore, our results demonstrate a strong resilience of plant-associated bacterial communities and of plants in response to bacterial invaders. Our study illustrates that inoculation experiments in the field with naturally occurring microbial communities of wild plants are suited to investigate complex interactions between microbial communities, the environment, and plant traits.