Physiological, morphological, and environmental variation among geographically isolated cottonwood (Populus Deltoides) populations in New Mexico

The ability of a plant population to respond and eventually adapt to enviro nmental stress ultimately determines that population's survival. This becom es especially significant in environments where important plant resource le vels have radically decreased. Southwestern riparian areas have numerous pl ant species that are experiencing radical changes in water availability due to construction of dams, and thus their ability to respond to such changes is critical. One such species likely to be greatly affected by these hydro logical changes is Populus deltoides var. wislizenii (cottonwood) because i t relies heavily on both groundwater and river surface volume as primary wa ter sources. Both water sources have been extremely impacted by impoundment s along Southwestern rivers. To understand how New Mexico populations of co ttonwood may respond to environmental changes, we quantified environmental differences and characterized physiological and morphological variation amo ng 4 cottonwood populations. Significant differences among study sites in w ater availability were indicated by both soil and groundwater salinity. The northernmost site, at Abiquiu, had the highest salinity levels in both soi l and groundwater, followed by Bernardo, while San Antonio and Corrales sit es had the lowest soil salinity. As expected, variation in physiological an d leaf morphological characters existed among and within the tree populatio ns, most likely in response to environmental factors. Midday xylem pressure potentials indicated that Abiquiu individuals suffered the greatest water stress and they also had the highest transpiration levels. Because of high specific leaf weights and high photosynthetic levels. cottonwoods at Corral es may better mitigate lower water availability. Such physiological and mor phological trait variability among populations is ecologically important an d may be of use in present reclamation and conservation efforts in these ar eas.