Document: DEN-3-32-24

Effects of early summer frosts on the hydraulic and stomatal conductance of a deciduous arctic species (Salix pulchra).

GORSUCH, D.M.* ¹, S.F.OBERBAUER ¹ and J.B.FISHER ²

Florida International University, Miami, FL, U.S.A. ¹
Fairchild Tropical Garden, Miami, FL, U.S.A. ²

Abstract:
Global climate change models predict that arctic spring temperatures will increase by 3 to 8C before the middle of the 21st century. Evidence is accumulating that climate warming is already occurring in Alaska. Enhanced growth of deciduous species under experimentally-elevated temperatures at the arctic LTER site suggests that the deciduous growth form will eventually dominate the arctic tundra community. This prediction, however, fails to account for the possibility of late frosts. Because of the limited length of their growing season and potentially larger conduit volumes, deciduous species are more likely than evergreens to be injured by freezing-induced cavitation early in the summer. We grew a deciduous arctic species (Salix pulchra) under elevated (+5C) and normal Alaska summer temperatures in controlled environments, and measured the hydraulic and stomatal conductance before and after a simulated freeze event. Hydraulic and stomatal conductance rates were significantly greater in the elevated-temperature plants before the freeze (P < 0.05). The difference between hydraulic conductance before and after the freeze in the elevated temperature treatment was 3.5 times greater than the difference in conductance in the normal treatment. Xylem anatomy data suggest that while vessel diameter and density were similar in plants grown under the two treatments, vessel length distribution was different. Percentage of vessel lengths in the smallest size class (0-2.5mm) was 91% for evergreens and 78% for deciduous species (P < 0.05). The results of this study may challenge the prediction that deciduous species will eventually dominate the arctic tundra.

Keywords: cavitation, hydraulic conductance, stomatal conductance, arctic tundra

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