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
Correlated evolution between leaf:xylem allometry and climate in woody plants.
Maherali, Hafiz*,1, Mencuccini, Maurizio2, 1 University of Guelph, Guelph, ON, Canada2 University of Edinburgh, Edinburgh, UK
ABSTRACT- The scaling relationship between leaf and stem area in plants reflects hydraulic coordination between transpiring surface area and the water conducting xylem. To prevent transpiration demands from exceeding water supply per unit leaf area, the leaf:sapwood area ratio(AL:AS) is predicted to decrease in response to increasing soil and atmospheric moisture deficits. To test whether this hypothesis has broad ecological and evolutionary support, we evaluated the relationship between AL:AS and several measures of soil and atmospheric moisture content for 75 species of woody plants from 15 seed plant families. To test for correlated evolution, we analyzed our data using phylogenetically independent contrast correlations calculated over a range of alternate seed plant phylogenies. In conifers, AL:AS decreased with increasing annual VPD (r = 0.43, P = 0.01, n = 36) and increased with increasing annual rainfall (r = 0.40, P = 0.02, N = 36) and relative humidity (r = 0.48, P = 0.004, n = 36). These relationships were also observed within both Pinus (n = 16) and non-Pinus (n = 20) conifers. In contrast, relationships between AL:AS and any climate parameter for the angiosperms were absent or quite weak (r = 0.01-0.22, P = 0.20-0.99, n = 39). We suggest that the coupling between hydraulically important allometric ratios and climate is strongest in the conifers because the canopies of these species are tightly coupled to prevailing atmospheric conditions. In contrast, the AL:AS – climate relationship may be weaker in angiosperms because xylem anatomy is more heterogeneous across groups or because low boundary layer conductance in broad-leaved canopies may buffer individuals from excessive atmospheric evaporative demand.
Key words: allometry, hydraulics, climate, evolution