Local Adaptation to Freezing in High and Low Latitude Populations of L. tridentata (Sevilleta National Wildlife Refuge, New Mexico; Higuerillas, Mexico) and L. divaricata (Bajada del Diablo and Chamical, Argentina) (2006-2009))

If freezing limits establishment of warm desert shrubs at high latitudes, shrubland distributions may be altered as a result of rising global temperatures. However, variation in plant physiology and morphology can be observed across climate gradients and may be acted on by selection to produce adaptation to local climate conditions, thereby ameliorating low temperature stress. Freezing damage in evergreens is closely linked to vessel size distribution because larger xylem conduits are more likely to become air-filled during freezing. In addition, plastic variation, rather than genetic, may be responsible for differences in freezing tolerance among populations. In order to determine if local adaptation to freezing is present in two species of the genus Larrea, L. tridentata and L. divaricata, we investigated xylem vessel size distributions in field grown L. tridentata adults and saplings grown in a common garden from high latitude (Sevilleta National Wildlife Refuge) and low latitude (Higuerillas, Mexico) sites in the Chihuahuan Desert in North America. High latitude (Bajada del Diablo, Argentina) and low latitude (Chamical, Argentina) populations of Larrea divaricata were selected for investigation from the Monte Desert in South America.