The plant-associated microbiome is known to influence plant physiology, metabolism and even plant species coexistence. The phyllosphere (i.e., aerial surfaces of plants, including leaves) is estimated to measure up to 4 x 10ˆ8 kmˆ2 in area globally. Although this habitat is oligotrophic, extremely poor in nutrients and exposed to a rapid and pronounced fluctuation of physical conditions, the phyllosphere microbiome (i.e., the microbial communities on and inside plant aerial tissues) represents one of our planet’s most diverse ecosystems. Previous research in phyllosphere ecology was limited by culture-dependent methods and systematically underestimated microbial population sizes and biodiversity, but recent improvements in culture-independent sequencing technologies have greatly contributed to the study of phyllosphere community structure and diversity. Microbes have been shown to participate in animal and plant population regulation, degrade environmental pollutants, contribute to host defense against pathogens and abiotic stressors, and synthesize compounds vital for plant productivity. In addition, the phyllosphere microbiome has been suggested to contribute substantially to both carbon and nitrogen cycles in terrestrial ecosystems. Recent studies have suggested that phyllosphere diversity could influence plant ecosystem productivity, hinting at a greater-than expected role for phyllosphere microbiota in global ecosystem dynamics. Our increased abilities to characterize these communities must now be balanced by greater research on their roles in driving plant resilience to episodic and extreme events, as well as in mediating tolerance to biotic and abiotic stressors. The speakers of this session will discuss the importance of phyllosphere microbiomes as important regulators of plant host fitness, productivity, and survival in the face of extreme events, as well as biotic and abiotic stresses. The goals of this session are to unite researchers studying bacterial, fungal, and plant ecology and synthesize what is known about the diversity, functional roles, and origins of plant-symbiont relations in the phyllosphere. This session is unique in that it focuses on biodiversity and ecosystem functioning within plant-microbial interactions at two different, but inherently connected, scales: 1) the macro-organismal scale, where plant and associated microbiota co-exist within a global ecosystem and 2) the micro-organismal scale, where the plant functions as an ecosystem itself. Additionally, the confirmed speakers of our session are diverse in terms of study system (including both agricultural and natural systems), research questions, and career stage, which will facilitate a dynamic and engaging atmosphere.