© 1991 Heron Publishing—Victoria, Canada
Gas exchange during a soil drying cycle in seedlings of four black walnut (Juglans nigra L.) families
William C. Parker (1) and Stephen G. Pallardy (2)
1. Weyerhaeuser Company, WCT-2B19, Tacoma, WA 98477, USA / 2. School of Natural Resources, University of Missouri-Columbia, Columbia, MO 65211, USA / Received February 17, 1991
Summary
Photosynthetic and stomatal responses to a soil drying cycle were examined in half-sib seedlings of four walnut (Juglans nigra L.) families. Well-watered seedlings of an Iowa seed source had significantly higher rates of net photosynthesis than seedlings
from New York or Michigan sources. This superior photosynthetic potential was associated with both greater stomatal conductance
and mesophyll capacity for CO2 fixation. In a drying soil, net photosynthesis and leaf conductance to water vapor of all families declined substantially,
even under mild water stress. These responses were more strongly related to soil water status, as estimated by predawn leaf
water potential, than to leaf water potential at the time of gas exchange measurement. There were no differences among families
in the pattern of gas exchange response to developing water stress; however, families differed in capacity for recovery of
gas exchange from water stress following rehydration. Sensitivity of photosynthesis of black walnut seedlings to water stress
may be associated with poor growth and survival of this species in xeric habitats.
