PARENT SESSION
Oral Session # 45: Plant Ecology III: Plant - Water Relations I.
Presiding: R Giuliani
Wednesday, August 6. 8:00 AM to 11:30 AM, SITCC Meeting Room 200.

Gas exchange rates and water relation responses of Juniperus ashei seedlings to drought.

Jurena, P.^*,1, Van Auken, O.¹, ¹ University of Texas at San Antonio, San Antonio, Texas, USA

ABSTRACT- The central Edwards Plateau, Texas, is dominated by Juniperus ashei woodlands which comprise > 40% of the canopy cover at ca. 1500 trees/ha. Survival is reported to be highest beneath the woodland canopy and decreased at the canopy edge but growth rates are highest at the canopy edge. Little is known of the drought response of J. ashei seedlings and its affects on spatial differences in growth and survival. Yearly mean photon flux density (PFD) measured beneath the canopy was 346.11±96.81 mol m^-2 s^-1. Soil moisture beneath the canopy was 34.82±3.72%. The light compensation point for J. ashei seedlings was between 25 and 50 mol m^-2 s^-1 PPFD and A_max (90%) was 4.48±0.03 mol m^-2 s^-1 at 750 mol m^-2 s^-1 PPFD. Soil moisture dropped from 43.3[plusmn:]1.5% to 7.6±1.0% through the greenhouse experiment. Seedling water potential started at −0.8±0.1 MPa and did not decline until after the soil moisture dropped below 20.5±3.6%(after three weeks). Gas exchange rates did not decline until three weeks after drought conditions were applied. Juniperus ashei seedling water potential and gas exchange rates appear to be decoupled from soil moisture levels.

Key words: drought, water potential, Juniperus ashei, gas exchange