PARENT SESSION
Contributed Oral Session 123: Photosynthesis and Water Relations: Leaf Architecture
Thursday, August 11, 8:00 AM - 11:30 AM, Meeting Room 522 A, Level 5, Palais des congrès de Montréal

Ecophysiology of Crassulacean acid metabolism (CAM).

Nelson, Elizabeth^*,1, Sage, Rowan¹, ¹ University of Toronto, Toronto, ON, Canada

ABSTRACT- Crassulacean acid metabolism (CAM) has evolved independently on dozens of occasions and is now found in over 7% of plant species. In this study, the leaf structure of a phylogenetically diverse assemblage of 18 CAM plants was compared with six C3 plants and four C4 plants to assess whether consistent anatomical patterns arise that may reflect functional constraints. CAM plants exhibited increased cell size and increased leaf and mesophyll thickness relative to C3 and C4 species. CAM species also exhibited reduced intercellular air space (IAS) and reduced length of mesophyll surface exposed to IAS per unit area (Lmes/area). The low volume of IAS and low exposure of mesophyll surface to IAS likely increases internal resistance to CO₂ in CAM tissues. While this diffusional barrier may limit uptake of CO₂ during Phases II and IV, carbon economy could be enhanced through the reduced loss of internal CO₂ during all four phases of CAM.

Key words: Crassulacean Acid Metabolism, leaf anatomy, intercellular air space, convergent evolution