Tree leaves as a habitat for phyllobacteria

Abstract Large populations of bacteria live on the leaf surface and play an important role in plant health and growth. These phyllobacteria are faced with extreme environmental conditions such as low moisture and nutrient availability, fluxes in ultraviolet radiation, high temperatures, etc., but have adapted to live in this habitat. The number of phyllobacteria and their species composition varies with host and geographical location. Generally, there is some correlation between the phylogeny of the tree host and the phyllobacterial composition. It is suggested that this is possibly driven by differences in leaf characteristics. Phyllobacteria can have a neutral, positive, or negative effect on their hosts. These effects include the production of phytohormones, biosurfactants, nitrogen fixation, and protection against abiotic and biotic factors. The focus of this review is on the leaf surface as a habitat for phyllobacteria, the bacterial community composition on tree leaves, and the role they play in this ecosystem.