67 Climatic Differences in Leaf Mass per Area in Various Coniferous Species across the United States.

Faculty Mentor: William Anderegg (Biology, University of Utah)

Climate change has increased the frequency of droughts and other extreme climatic events over time. Understanding how forests respond to these stressors is critical to understanding landscape and environmental changes. Leaf mass per area (LMA) is a common metric for understanding how plants respond to drought stress. Understanding LMA across different species and climates can help better inform the strategies used by plants to maximize photosynthetic abilities while minimizing water loss. This study examines how different variables interact with LMA using five coniferous species across various climates. Using 57 samples we collected, we calculated the leaf mass per area. Then, we used INaturalist detection data of the species we studied and daily GridMET climate data to evaluate differences in LMA between these five species across the United States. We considered precipitation, temperature, and vapor pressure deficit (VPD). We found that species that occupy ranges with higher VPD and maximum annual temperature had lower LMA on average. Average annual precipitation does not trend as strongly with LMA as initially anticipated in the five species we studied. Trees that occupy zones with higher VPD are at higher risk of drought stress, which is interesting as high LMA is associated with having leaves that have much denser tissues. Since the trees we sampled that have lower LMA are found in high VPD environments, future studies could look at anatomical differences in their water conducting systems or their root systems to understand how they might be coping. Also, looking at stomatal conductance across these species to better understand how their gas exchange is affected could provide further insight into changes plants may undergo in these conditions. Furthermore, looking at average low temperatures to investigate differences between average high and low trends would be insightful, considering the strong trend observed in relation to maximum temperatures. Knowing how these variables affect LMA in different species can help build a more robust understanding of key physiological characteristics that drive their success as more stressful conditions intensify.