Climate-driven shifts in vapor pressure deficit tolerance may favor invasive E. angustifolia over native P. fremontii
Rebecca Senft1*, Brandt Winn1, Kevin Hultine2, and Luiza Aparecido1
Affiliations:
1. School of Biological Sciences, University of Utah, Salt Lake City, UT 84112
2. Department of Research, Conservation and Collections, Desert Botanical Garden, Phoenix, AZ 85008
Riparian ecosystems are highly vulnerable to invasion as they experience a high level of disturbance (i.e., seasonal flooding) and an excess of resources (e.g., water and nutrients), providing ideal conditions for non-native plants to establish. This invasion risk may be intensified by shifting climates, as invasive species are often believed to acclimate more efficiently to environmental stressors. In the western US, Elaeagnus angustifolia, commonly known as Russian olive, has become a common invasive tree species, inhabiting many riparian ecosystems. However, little work has been done to explore whether this invasive species may be better suited to climate stress than co-occurring natives. Here, we asked whether the invasive E. angustifolia would have an ecological advantage over the native Populus fremontii, commonly known as Fremont Cottonwood, by being more physiologically adapted to climate extremes. Specifically, we hypothesized that E. angustifolia would be 1) less sensitive to vapor pressure deficit (VPD) and 2) more thermotolerant than P. fremontii. To test this, we established three field sites on the Paria River in the Grand Staircase Escalante National Monument (located in southern Utah) where both species co-occur. We collected leaf gas exchange (photosynthesis, stomatal conductance) and weather data during the 2024 and 2025 growing season to quantify both species’ responses to changes in VPD. Concurrently, we collected Tcrit, a measurement of the temperature at which photosystem II begins to degrade, to assess which species was better suited to survive thermal stress across this elevation-temperature gradient. We found that stomatal conductance and photosynthesis of E. angustifolia were less sensitive to increases in VPD when compared to P. fremontii, supporting Hypothesis (1). However, Tcrit did not differ between species and seasonality, rejecting Hypothesis (2), indicating that differences in photosynthetic performance were not driven by the risk of damage to photosystem II. This work indicates that E. angustifolia is more likely to continue photosynthesizing in harsher future climates, and that this difference may be driven by specific water use strategy as opposed to declines in the structure of photosystems. The higher adaptability of E. angustifolia to climate extremes may allow for intensified growth and spread of the invasive species in climate change scenarios, placing additional pressure on P. fremontii and other ecologically important riparian species.