Plant and Soil Drivers of Whole-Plant Microbiomes: Variation in Switchgrass Fungi from Coastal to Mountain Sites

Plant-associated microbial diversity is regulated by dispersal from local and regional species pools, as well as filtering by the environment and plant host. However, few studies have simultaneously examined microbial community variation in multiple plant-associated habitats across multiple sites; thus, it is unclear what scales and filters are most important in shaping whole-plant microbiome diversity. To address this, we characterized fungal communities associated with switchgrass (Panicum virgatum L.) leaves, roots, and soils within and across 14 stands spanning mountain to coastal ecoregions of North Carolina. Niche differences at small scales (i.e., less than half a kilometer) best explained variation in fungal communities. However, the specific environmental drivers of fungal community composition differed for leaves, roots, and soils. Leaf and root fungi were both affected by plant height, whereas soil fungi were controlled by stand age. Different soil properties were important for fungi in all plant-associated habitats: K, P, and pH for leaves; clay, Mn, and pH for roots; and clay, dissolved organic carbon, total inorganic N, and Cu for soils. Climate and spatial variables were not significant, further supporting the key role of plant and soil properties. Advances such as these will help us explain, predict, and manipulate microbial assemblages that support plant growth in managed and natural systems.