The phyllosphere, a reservoir of diverse microbial life associated with plant health, harbors microbial communities that are subject to various complex ecological processes acting at multiple scales. In this study, we investigated the determinants of the spatiotemporal variation in bacterial and fungal communities within the apple tree phyllosphere, employing 16S and ITS amplicon sequencing. Our research assessed the impact of key factors-plant compartment, site, time, and cultivar-on the composition and diversity of leaf and flower microbial communities. Our analyses, based on samples collected from three cultivars in three orchards in 2022, revealed that site and time are the strongest drivers of apple tree phyllosphere microbial communities. Conversely, plant compartment and cultivar exhibited minor roles in explaining community composition and diversity. Predominantly, bacterial communities comprised Hymenobacter (25%) and Sphingomonas (10%), while the most relatively abundant fungal genera included Aureobasidium (27%) and Sporobolomyces (10%). Additionally, our results show a gradual decrease in alpha-diversity throughout the growth season. These findings emphasize the necessity to consider local microbial ecology dynamics in orchards, especially as many groups worldwide aim for the development of biocontrol strategies (e.g., by manipulating plant-microbe interactions). More research is needed to improve our understanding of the determinants of time and site-specific disparities within apple tree phyllosphere microbial communities across multiple years, locations, and cultivars.
Keywords: Malus domestica; bacteria; fungi; microbial ecology; phyllosphere; spatiotemporal variation.