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

Physiological trait variation in Sonoran Desert winter annuals.

Barron-Gafford, Greg^*,1, Gerst, Katharine ^*,1, Huxman, Travis¹, Venable, D. Lawrence¹, ¹ University of Arizona, Tucson, AZ

ABSTRACT- The winter annual plant community makes up approximately 50% of the Sonoran Desert flora. Demographic data collected over the past 21 years at Tumamoc Hill near Tucson, AZ has demonstrated distinct life history syndromes between species within this community operating through differential germination and reproductive responses to temporal variation in precipitation. This study examined differences in physiological traits underlying carbon and water exchanges with the environment among species of a guild of desert winter annuals that demonstrate variable responses to precipitation. In particular, we looked at the relationship between photosynthetic carbon gain, leaf nitrogen content, and specific leaf area throughout the ontogeny of multiple species through the growing season. We hypothesized that the photosynthetic response and water use efficiency of annual species would correlate to the variable reproductive strategies elucidated by demographic studies. We constructed A-Ci curves on 12 species at the beginning and end of the winter growing season. This allowed us to determine CO₂ saturated rates of photosynthesis (Amax), the efficiency of carboxylation by rubisco (CE), and the relative degree of photosynthetic limitation by stomatal conductance. Early in the growing season, Amax values ranged between 19-58 mol m^-2s^-1, CE values ranged between 0.07-0.13 mmol m^-2s^-1, and stomatal limitation ranged between 0.001-0.28 %. Preliminary results suggest these large ranges correspond with differences in both functional and life history traits derived from the demographic data. By merging our knowledge of population dynamics within this community with an analysis of functional trait variation, we are beginning to develop a more complete understanding of the complex ecological and physiological mechanisms involved in species co-existence.

Key words: ecophysiology, photosynthesis, annuals, population dynamics