Presentation description

As climate change increases the frequency of extreme heat events, understanding plant thermotolerance mechanisms becomes crucial. Plants under such conditions are particularly vulnerable to photosynthetic tissue damage, such as Photosystem II (PSII), threatening their survival and ecological function. Plant thermotolerance determination techniques have significantly improved in the past decade, with critical temperatures (TCrit) being one of the parameters used as a metric for leaf thermotolerance. However, the necessary equipment is not readily available to most, and more accessible techniques are cumbersome and susceptible to various methodological errors. Thus, many questions remain on the appropriate sampling and methodological techniques required to obtain the accurate TCrit values.
Here, we evaluated thermotolerance across several plant species by measuring chlorophyll fluorescence, using the closed FluorCam system (FC-800, PSI, Czech Republic), testing various TCrit methodological protocols. We investigated the effects of (1) post-collection time (leaf degradation over time), (2) canopy height, (3) leaf age and (4) time of year on TCrit. The leaf samples were collected from trees (14 species) easily accessible on the University of Utah campus and arboretum, and were brought and measured in the lab.
We found that:
1. Time since collection significantly alters TCrit, with some species showing a sharp decline after prolonged storage, while others remained constant.
2. Canopy height had no significant effect on TCrit, even among leaves with distinct morphologies.
3 .Leaf maturity impacts thermotolerance, with mature leaves exhibiting higher TCrit than younger leaves.
4. Time of year significantly impacted species TCrit differently, with some species acclimating with increasing summer temperatures while others declined.
These results highlight the importance of methodological consistency in fluorescence-based thermotolerance studies. Future research should extend trial durations and incorporate a broader range of species to further validate these findings.