PARENT SESSION
Poster Session 1: Photosynthesis and Water Relations
Monday, August 8, 5:00 PM - 6:30 PM, Exhibit Hall 220 A-E, Level 2, Palais des congrès de Montréal

Light response of Juniperus ashei along a light gradient.

Jurena, Paul^*,1, Furuya, Mitsuru¹, ¹ University of Texas at San Antonio, San Antonio, Texas, USA

ABSTRACT- The central Edwards Plateau, Texas, is dominated by Juniperus ashei which comprise > 40% of the canopy cover. Seedling survival is highest beneath woodland canopies and decreases at canopy edge with growth rates highest at canopy edge. In greenhouse experiments, drought response of J. ashei seedlings is gradual over a four week period in terms of carbon gain and appears to be uncoupled from soil moisture. Recovery from this drought is rapid with carbon gain after 72 hrs. The light response of J. ashei seedlings in photosynthetic rate (±SE for all data) was 4.56±0.53 mol CO₂ m^-2 s^-1 at 1500 mol m^-2 s^-1 PPFD and declined rapidly after 750 mol m^-2 s^-1 with a light compensation point at 25-50 mol m^-2 s^-1. Little is known of responses of juvenile J. ashei plants to light levels in the field and may be important to understand general distribution and expansion of this species. Soil moisture was 24.0±2.3% in open, 28.0±3.4% at canopy edge, and 34.8±3.7% under canopy. The light levels were 1295±10 mol m^-2 s^-1, 1234±11 mol m^-2 s^-1, and 52±11 mol m^-2 s^-1 (same order as above). At the highest light levels (2000 mol m^-2 s^-1), J. ashei juveniles at canopy edge had the highest photosynthetic rates (5.1±1.1 mol CO₂ m^-2 s^-1) followed by open (3.9±1.1 mol CO₂ m^-2 s^-1) and under canopy (1.8±1.0 mol CO₂ m^-2 s^-1). Juvenile plants in open never displayed a saturation point within range of light levels used (0-2000 mol m^-2 s^-1). The saturation point for edge plants was 1000 mol m^-2 s^-1 and was 100 mol m^-2 s^-1 PPFD for canopy plants. The light compensation point for juvenile plants appears to be between 10-20 mol m^-2 s^-1 PPFD. The experiment indicates that J. ashei juveniles responded similarly to the seedlings in the canopy and edge locations but appear to be not to light saturate when exposed to high light environments giving this species flexibility to light levels.

Key words: Juniperus ashei, Edwards Plateau, Light Response, Photosynthesis