Physiological strategies during frost periods for two populations of Prosopis burkartii, an endangered species endemic to the Atacama desert

The occurrence of frost during the winter months is among the most limiting factors for plant growth and establishment in arid climates. In this context, we evaluated the variation in the physiological parameters in two populations of Prosopis burkartii-a species that is listed as critically endangered -during the frost-prone winter periods of 2012 and 2013 at the within- and between population levels. A total of 30 mature individuals representing approximately 70% of the existing population of this species were selected to measure the stem water potential (Ψ), cuticular transpiration (Ec), pressure-volume curves, and specific leaf area (SLA). At the between population level, differences in the SLA and Ψ were measured during the months that had the most days with temperatures below 0 °C. By contrast, at the within population level, differences in the Ec values, osmotic potential at full turgor (Ψπfull), and relative water content at the turgor loss point (RWCtlp) were significant. The variations in SLA indicated an increase in the nonstructural biomass during the months with the greatest number of frost days. This increase was interpreted as a measure of the solute accumulation that is associated with sustaining the population at low temperatures. The detected within population differences denote the variety of individual responses in the Prosopis genus for accumulating solutes and conserving water during periods of stress. This variability is likely a consequence of the high genetic variability that has been documented in previous studies for this genus.