Variation in physiological, morphological, and demographic traits among cottonwood populations in New Mexico: Evidence for an environmental and genetic basis of variation

By determining the environmental and genetic basis of trait variability, we can answer questions about a species evolutionary potential, its range in phenotypic plasticity, and conservation possibilities. I determined demographic, physiological, and morphological trait variability among five Populus deltoides populations along the Rio Grande basin in New Mexico at Abiquiu, Corrales, Los Lunas, Bernardo, and San Antonio. At each site, ten randomly spaced plots were established and all individuals within these plots were tagged, measured for size (DBH), distance to the river, and censused by sex. There was significant variation in tree size and basal area density among sites. Sex ratio was biased at only one site (Abiquiu) in 1995; the other populations had relatively even sex ratios over three years. However, there was significant variation among sites in percent reproduction, changes in reproductive status, sexual lability, and percent mortality. These data indicated that sex ratio may not always be indicative of stress in this environment.; Along with these demographic differences among populations, I found environmental and physiological variation. Significant differences among populations existed in soil and groundwater salinity, groundwater depth and amount, gas exchange physiology, and leaf morphological characters. There was correlative evidence that the physiological variation among sites was due, in part, to environmental differences.; In order to determine the genetic basis of physiological variation among sites, I grew clones from the trees measured for physiology in a common garden. Significant population-specific variation occurred for gas exchange and leaf morphological traits in 1996 and 1997. Several physiological and morphological traits differed among the sexes in both years, and indicated that trees that remained non-reproductive in the field for three years may be drought adapted.; This study demonstrated the existence of variation in demographic, physiological, and morphological traits among several populations of cottonwood in New Mexico. There was also evidence for an environmental and genetic basis of trait variation among populations and a genetic basis to trait variability among cottonwoods of differing reproductive status. Such results have ecological and conservation importance.