Diversity in physiological and morphological characteristics of four cottonwood (Populus deltoides var. wislizenii) populations in New Mexico: evidence for a genetic component of variation

A common garden was established using 120 genotypes of Populus deltoides var. wislizenii (S. Wats.) Eckenwalder from four New Mexico populations (Abiquiu, Corrales, Bernardo, and San Antonio) to examine physiological and morphological differentiation within and among populations. All populations were located within the same watershed along the Rio Grande and one of its tributaries, the Rio Chama. In the common garden, I measured physiological and morphological variation during the 1996 and 1997 growing seasons to determine the extent of inter- and intra-population variation in these traits. In addition, because the sex of each source tree from the field was known, I was able to determine if these same traits varied among male, female, and nonreproductive trees. Small but significant differences within and among populations occurred for photosynthesis, transpiration, and stomatal conductance in both years. Leaf morphological traits also differed within and among populations, including leaf size, chlorophyll content, and specific leaf mass. Stomatal conductance differed significantly between female and nonreproductive trees in both years. This study demonstrated the existence of genetic variation in ecophysiological and morphological traits within and among cottonwood populations and among cottonwoods of differing reproductive status within a single watershed.