Seasonal variation in stomatal sensitivity to atmospheric aridity between native and non-native riparian tree species in the western US
Susan E. Bush1,2, Jessica S. Guo3, Kevin R. Hultine1
1Department of Research, Conservation, and Collections, Desert Botanical Garden, Phoenix, AZ 85008, USA
2Department of Biological Sciences, University of Utah, Salt Lake City, UT 84112, USA
3Arizona Experiment Station, College of Agriculture and Life Sciences, University of Arizona, Tucson, AZ 85721, USA,
Riparian forests are among the most productive and biodiverse ecosystems of the arid western US, yet their future community structure and function is uncertain given past and ongoing introduction of non-native species as well as increasing aridity with climate change. Because plant stomata dynamically regulate carbon uptake with water supply, quantifying species-specific stomatal sensitivity to atmospheric aridity (atmospheric vapor pressure deficit, D) is a necessary component for predicting possible future changes in groundwater dependent ecosystems across the western US landscape. Using sap-flux data for nine dominant riparian species from four sites spanning an elevation gradient in northern Utah, we fit a time-varying empirical model of stomatal conductance to D. Species included seven native species with diffuse-porous wood anatomy (Acer grandidentatum, Populus angustifolia, Betula occidentalis, Acer negundo, Salix hybrid, Populus hybrid, Populus fremontii) and two non-native species with ring-porous wood anatomy (Tamarix ramosissima, Elaeagnus angustifolia). Our results showed three patterns of standardized stomatal sensitivity (S) with cumulative D over time. All native, diffuse-porous species showed either a positive correlation between S and cumulative D or no change in S with cumulative D over time. In contrast, the two ring-porous, invasive species showed a negative correlation between S and cumulative D over time. These results are among the first to demonstrate that stomatal sensitivity to D can vary significantly over the course of a single growing season and may have important implications for future tree community structure in western riparian forests. Given that the two ring-porous, non-native species were the only species to show decreasing S with cumulative D over time indicates that a progressive increase in aridity across the western US could amplify the competitiveness of these two highly invasive tree species relative to native tree taxa.