Physiological functioning of Fraxinus americana among ten populations across a large precipitation gradient in a common garden

Background/Question/Methods

Mean annual precipitation is projected to shift across North America over the next century with total annual precipitation very likely to increase in the northeastern U.S. and likely to decrease in the southwestern U.S.; however, it is also predicted that precipitation events will be more episodic across the U.S.  Populations of plant species with large distributions will likely be impacted differently across the species range to variability in precipitation events.  Because precipitation is a major determinant of plant growth and physiological functioning, it is critical to understand how populations of species with large distributions may respond differently to precipitation shifts across a species range in order to accurately predict physiological responses to future climate change scenarios. The overall objective of this study was to investigate population-level variation in physiological functioning of a dominant tree species in the U.S., Fraxinus americana (white ash).

Results/Conclusions

Leaf-level gas exchange and water potentials were measured among ten white ash populations across a west-east precipitation gradient (approximately 700 mm total annual precipitation) in a large common garden experiment (43 populations total) located at the extreme western edge of the species range in Jefferson, KS, U.S. Measurements were taken across the summer (June-August) during an above-average wet year (2013) at the common garden. Average mid-day water potentials among the eight populations ranged from -2.5 to -2.9 MPa, but were not significantly different among populations. We also did not find any significant differences in leaf-level gas exchange (A_max, g_s, C_i) between eastern and western populations in the common garden. Similar results for instantaneous physiological measurements were found at this site for these same populations in 2005.  Future work will include analyses of physiological responses to interannual variation across wet and dry years at the common garden site.