Document: JOS-3-30-9

Individual responses to water deficit in the riparian tree Populus fremontii.

LEFFLER, A.J.*

Utah State University, Logan, UT, USA ¹

Abstract:
Long-term water deficits in western US riparian forests are relatively recent. Prior to damming and channelization of rivers, significant water would become available in the spring as a result of snowmelt. Over the past century, however, increasing amounts of water have been removed from these rivers for anthropogenic uses and low water availability is now a common occurrence. The riparian tree Populus fremontii (Fremont cottonwood) is susceptible to drought because it is not adapted to low water conditions. Variation among individuals in response to low water availability may, however, exist in a population allowing subsequent generations to better cope with drought. To examine this possibility, 10 individuals were selected from a central New Mexico cottonwood population and cuttings were grown in a greenhouse. Once leaves were present, the cuttings were subjected to either high or low water conditions. After growing for approximately two months, gas exchange, leaf chlorophyll content, leaf area and carbon isotope composition were measured to determine the impact of low water availability on the different individuals. As expected, all individuals exhibited a decline in physiological activity in the low water treatment compared to those that received ample water. Not all individuals, however, responded to the same degree. Specifically, I observed a significant individual treatment interaction for the traits of transpiration rate, water use efficiency and substomatal [CO₂] suggesting some individuals responded to drought to a greater extent than others. These data suggest that P. fremontii exhibits a large degree of variation among individuals in their response to drought. This physiological variation, if it is heritable, may be of evolutionary importance since drought tolerant individuals are at an obvious advantage in western US riparian forests.

Keywords: drought, gas exchange, intrapopulation variation, riparian trees

This abstract is being presented at: 3:30 PM in session:
WATER RELATIONS