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Biology of Dryland Plants

Edwards, Erika [1].

Pereskia water relations reflect deep ecophysiological conservatism in Cactaceae.

Pereskia (Cactaceae) comprises 17 species of leafy shrubs and trees that form a paraphyletic grade at the base of the cactus lineage, and are often interpreted as our best extant representatives of ancestral cacti. It has been assumed that Pereskia water relations are unlike those of a leafless, stem-succulent cactus, as Pereskia species lack the anatomical specializations and CAM photosynthesis that are associated with the high water storage capacity and photosynthetic water use efficiency (WUE) exhibited by the core cacti. We have measured several important water relations parameters (e.g., WUE, leaf (Kl) and stem (Ksp) specific xylem hydraulic conductivity, Huber value (Hv), and leaf water potential (Psimin)) from field populations of 7 species of Pereskia representing all three major Pereskia clades. The data suggest that Pereskia species exhibit a typical cactus-like ecological water use ?strategy?: they maintain high photosynthetic tissue water potential while living in water-limited environments by supporting transpiring leaves with an efficient and reliable water delivery system, and by only opening stomata when transpirational demand is reduced. The basal placement of Pereskia within Cactaceae indicates that this ecological strategy was established very early during cactus evolution, and may have enabled the later development of the anatomical specializations that characterize the core cacti. Analyzing these data within a phylogenetic context additionally allows for new inferences regarding the relationships between Ksp, Kl, Hv, and Psimin during evolutionary shifts into wetter or drier areas. In the case of Pereskia, Psimin is remarkably constant across all species, regardless of differences in habitat annual rainfall or daily VPD. High Psimin is maintained primarily by shifts in Kl and Hv rather than Ksp, suggesting that Pereskia species are more likely to respond to changes in transpirational demand by altering carbon allocation patterns and leaf size rather than wood anatomy.


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1 - Yale University, Department Ecology & Evolutionary Biology, Po Box 208105, New Haven, Connecticut, 06520-8105, USA

Keywords:
Pereskia
Cactaceae
xylem hydraulic conductivity
physiological evolution
Phylogeny
water relations.

Presentation Type: Symposium or Colloquium Presentation
Session: 41-5
Location: Salon K - Austin Grand Ballroom/Hilton
Date: Wednesday, August 17th, 2005
Time: 9:15 AM
Abstract ID:228


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