Search for: All records

Summary Populus fremontiiis among the most dominant, and ecologically important riparian tree species in the western United States and can thrive in hyper‐arid riparian corridors. Yet,P. fremontiiforests have rapidly declined over the last decade, particularly in places where temperatures sometimes exceed 50°C.We evaluated high temperature tolerance of leaf metabolism, leaf thermoregulation, and leaf hydraulic function in eightP. fremontiipopulations spanning a 5.3°C mean annual temperature gradient in a well‐watered common garden, and at source locations throughout the lower Colorado River Basin.Two major results emerged. First, despite having an exceptionally highT_crit(the temperature at which Photosystem II is disrupted) relative to other tree taxa, recent heat waves exceededT_crit, requiring evaporative leaf cooling to maintain leaf‐to‐air thermal safety margins. Second, in midsummer, genotypes from the warmest locations maintained lower midday leaf temperatures, a higher midday stomatal conductance, and maintained turgor pressure at lower water potentials than genotypes from more temperate locations.Taken together, results suggest that under well‐watered conditions,P. fremontiican regulate leaf temperature belowT_critalong the warm edge of its distribution. Nevertheless, reduced Colorado River flows threaten to lower water tables below levels needed for evaporative cooling during episodic heat waves.