Do Leaf Temperatures Determine Endophyte Composition and Richness in Florida Native Plant Species?

Microbiomes play crucial roles in ecosystems, largely through their interactions with plants. Fungal endophytes occur in nearly all plant tissues and can influence host physiology, stress tolerance, and productivity. Although previous studies have examined how air temperature shapes foliar endophyte communities, endophytes may respond more strongly to leaf temperatures, which are often decoupled from ambient air temperatures. Consequently, changes in leaf temperature (e.g., due to global warming) may alter endophyte diversity and composition. In this study, we experimentally tested whether elevated leaf temperatures affect fungal endophyte richness and community composition in six native subtropical plant species from South Florida. Using in situ localized heating of individual branches, we increased leaf temperatures by 1°C-3°C over a 2-week period. Leaf thermal profiles were monitored with thermal imaging, and pre- and post-treatment leaf samples were collected from warmed and control branches for fungal DNA extraction, ITS sequencing, and community analysis. Our results show that fungal leaf endophyte richness and composition were strongly determined by host plant identity, but were unaffected by warming. Linear mixed-effects models and paired t-tests showed no significant changes in ESV richness with heating across all hosts. Similarly, distance-based redundancy analysis and PERMANOVA tests revealed no significant shifts in fungal community composition due to increased leaf temperatures. However, a random forest classification model identified a subset of fungal ESV that were predictive of temperature treatment. While overall endophyte communities were stable, specific taxa may be thermally responsive. Foliar fungal endophyte communities in subtropical woody plants may be resistant to short-term warming. Such stability could buffer host plants against microbial disruption during temperature extremes, though it may also limit adaptive microbial turnover. This study advances understanding of plant-microbe thermal dynamics and underscores the need for further research on the functional resistance of endophyte communities under climate change.