Faculty Mentor: William Anderegg (School of Biological Sciences, University of Utah)

Anthropogenic warming has significantly increased wildfire frequency and severity; climate change is responsible for nearly half of the wildfire-burned area in the western United States. Extreme wildfire events lead to prolonged smoke exposure, impacting tree physiology by altering photosynthetic processes. Past research on the impacts of smoke on tree physiology has found paradoxical results: smoke can both inhibit and enhance photosynthesis, as light scattering by aerosols can enhance photosynthesis, and reductions in photosynthetic activity are possible through biochemical disruptions. Additionally, particulates found in smoke can become embedded on the leaf’s surface, increasing leaf water loss.

This research investigated the relationship between smoke exposure and tree physiology, aiming to clarify the broader impacts of anthropogenic warming on ecosystem stability and forest resilience under changing climatic conditions. This study seeks to understand the effects of varying smoke intensities on Pinus ponderosa photosynthetic traits. Key physiological metrics, such as chlorophyll fluorescence, thermotolerance, photosynthetic efficiency, and cuticular conductance, are used to assess overall tree help and plasticity after exposure to a smoky environment.

Results show that low-intensity smoke had minimal effects on chlorophyll fluorescence (Fv/Fm), while high-intensity smoke led to increased variability and a significant pre-dawn decline, suggesting impaired Photosystem II function. Cuticular conductance (gmin) increased significantly under low smoke exposure, possibly due to aerosol-induced cuticle damage or incomplete stomatal closure. Still, surprisingly, no significant change of gmin was observed under high-intensity treatment. This divergence suggests concentration-dependent effects of smoke aerosols on leaf water regulation. Additionally, the impact of smoke introduces substantial variability into multiple metrics of leaf health and raises questions regarding the carbon assimilation process.

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