In the Ball Field (or alternative site, determined in cooperation with UMBS staff), I will plant 96 P. serotina seedlings, which I will source from Cold Stream Farm (Free Soil, MI). Within this planting series, I will implement the following treatments to manipulate the trophic levels present: P. serotina with both fungus and mites present, just fungus present, just mites present, and neither mites nor fungus present. I will nest this trophic manipulation within a warming manipulation, such that half of the plants receive warming. In total, there will be 8 treatments, with 12 P. serotina replicates in each treatment. To remove foliar fungi from a portion of the plants, I will apply Quilt fungicide, a broad-spectrum fungicide used in similar experiments, biweekly throughout the growing season (Kohli et al., 2021). To remove mites from a portion of the plants, I remove domatia by shaving the tufted structure from the surface of the leaves to prevent mites from colonizing domatia, a common method to reduce mite abundance (Walter, 1996). To elevate temperature, I will establish open-top chamber warming plots to elevate the temperature within the plots to +3℃, in line with expected warming for the region (IPCC, 2014). Nested within these plots, I will include one replicate of each trophic manipulation. I will use six TMS-4 probes (Wild et al., 2019) to record the temperature and humidity in of a subset of plots. I will establish the P. serotina seedlings in early June and will complete data collection in late August, which coincides with the peak time of domatia occupancy by mites. At the end of the season, I will sample a subset of 3 leaves from each plant and quantify domatia length, the mite community, and the fungal community on each leaf. To quantify domatia length, for leaves that have domatia intact, I will measure the length of the domatia along the midrib of each leaf. To quantify the mite community, I will examine the surface of the leaf and count the number of mites present. I will then sort mites into morphospecies and use molecular DNA barcoding to identify mites to species (Graham et al., 2022). To quantify the fungal community, I will use tape along the underside of the leaf to extract mycelium, and then count the number of hyphae along a transect of the tape to determine fungal community abundance (Graham et al., 2022). I will then extract 8 5-mm leaf discs from each leaf, which I will then dry and mill to a fine powder that I will use for DNA extraction to characterize the foliar fungi community composition (Gaytán et al., 2022). At the beginning and end of the growing season, I will measure plant height and diameter to quantify how warming and trophic interactions affect plant growth. Space permitting, I will leave the P. serotnia seedings in place through the 2025 field season and replicate the above data collection. At the end of the 2025 field season, I will remove the seedlings and measure total biomass of all seedlings. Note that the seedlings will not flower nor set seed during this time interval. I will also conduct a survey of naturally occurring domatia-bearing plant species at field sites throughout and adjacent to UMBS. Taking advantage of the diversity of field sites and experimental manipulations at UMBS, I will examine how variable environmental conditions across sites influence the plant-mite mutualism. For example, within the Forest Resilience Threshold Experiment at UMBS, gradients of manipulated canopy tree defoliation likely change the microclimate of the understory (von Arx et al., 2013). As such, manipulations of these plots are just one example of an existing gradient of abiotic conditions at UMBS which could influence domatia size, mite community composition, and fungal community composition. At ~20 sites throughout UMBS, I will collect leaves from wild domatia-bearing plant species. At each site (with permission from investigators at sites with experiments occurring), I will haphazardly collect 3 leaf samples per available domatia-bearing plant. I will then repeat the above-described methods to assess domatia, mites, and fungus respectively for each leaf. At each site, I will assess temperature and relative humidity at the time of sampling using a portable Traceable Thermohydrometer (Webster, TX) to assess relative conditions across sites, accounting for differences in ambient conditions by day.