Evidence for Local Adaptation in Hydraulic Architecture of non-native Tamarix Spp.; Emily Johnson

 

 

Emily Johnson¹*, Julia Hull¹, Kevin Hultine²

 

¹Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, USA; emj98@nau.edu

² Department of Biological Sciences, Northern Arizona University, Flagstaff, AZ, USA; julia.hull@nau.edu

³ Desert Botanical Garden, Phoenix, AZ, USA; khultine@dbg.org

 

 

Poster Abstract (Adaptive Management Outcomes): Since their introduction to North America in the early 19^th century, species of the genus Tamarix (tamarisk) have invaded riparian ecosystems across a uniquely extreme climate gradient in the southwestern US. Episodic heat waves in lower elevations and freezing events in higher elevations, both of which likely to increase in frequency and intensity in the current climate trend, can exert significant limitations in plant hydraulic function.  The high vapor pressure deficit (VPD) that accompanies a high mean maximum annual temperature (MMAT) creates a pressure-driven demand for atmospheric moisture – yielding high transpiration rates relative to stomatal conductance. Likewise, exposure to spring frost events can disrupt water transport from rhizosphere to canopy. The root surface area (A_r) to leaf surface area (A_l) ratio (A_r:A_l) in local tamarisk populations may be responding to these environmental pressures. Therefore, we hypothesize that tamarisk genotypes sourced from higher elevations will have higher A_r:A_l than genotypes from lower elevations. A common garden experiment in Yuma, Arizona hosting tamarisk genotypes sourced from four populations across an elevation gradient of 49 m to 1,643 m was established. Total root area from multiple soil depths and total leaf area were analyzed and extrapolated to quantify population A_r:A_l. Two patterns of potential local adaptation in tamarisk hydraulic architecture emerged. 1) There is a positive correlation between elevation and A_r:A_l (R²=0.99). 2) A_r:A_l  was also correlated with average climatic factors in a 30 year model (e.g. VPD, MMAT R² = 0.97 & 0.97, respectively). These patterns indicate that the A_r:A_l is under genetic control, and that high-elevation tamarisk populations cope with frost by allocating more biomass belowground relative to low elevation populations. This study implies that local adaptation in hydraulic architecture is a key component in understanding the success of non-native tamarisk across American southwestern riparian ecosystems.