PARENT SESSION
Oral Session #31: Plant Ecology: Gas Exchange.
Presiding: R. Montgomery
Tuesday, August 6. 8:00 AM to 11:30 AM. Cochise Meeting Room, TCC.

Influences of whole plant water transport and drought on gas exchange within a chaparral community.

Bhaskar, Radika^*,1, Tirado-Fernandez, Reyes², Cavender-Bares, Jeannine³, Zlatnick, Daniel¹, Preston, Katherine¹, Ackerly, David¹, ¹ Stanford University, Stanford, CA² Estacion Experimental do Zonas Aridas (CSIC), Almeria, Spain³ Smithsonian Environmental Research Center, Edgewater, MD

ABSTRACT- Under conditions of drought, the ability to regulate water use is of critical importance to plant performance. Plants must balance water supply from the roots with transpirational demand to prevent severe declines in leaf water potential and negative consequences for carbon gain. However increases in water supply through greater whole plant hydraulic conductance may incur costs associated with increased xylem vulnerability to embolism. We examined water relations and gas exchange in thirteen co-occurring chaparral evergreens that vary in leaf function and access to water (rooting depth). Across species, we found water supply to the leaves (whole plant conductance) was positively associated with leaf water loss (maximum rates of transpiration). Increased rates of water supply and loss were negatively correlated with maximum degree of drought stress as indicated by the minimum diurnal water potential. Whole plant conductance was positively correlated with maximum photosynthesis as well. However, smaller-leaved species achieved higher carbon gain relative to water loss and whole plant conductance. These patterns suggest a secondary aspect of differentiation in water use strategies involving leaf size.

KEY WORDS: chaparral, drought, water relations, conductance