PARENT SESSION
Contributed Oral Session 16: Photosynthesis and Water Relations: Conductivity; Stress
Monday, August 8, 8:00 AM - 11:30 AM, Meeting Room 524 A, Level 5, Palais des congrès de Montréal
Height-related variation in photosynthetic characteristics of Sequoia sempervirens leaves.
Koch, George *,1, Sillett, Stephen 2, Antoine, Marie2, , , , , , , 1 Northern Arizona University, Flagstaff, AZ, United States2 Humboldt State University, Arcata, CA, United States
ABSTRACT- Strong vertical gradients in light level and water potential are present within the crowns of tall trees. In redwood, Sequoia sempervirens, these gradients are associated with vertical variation in the structure of leaves, which range from flat, relatively thin, needles arrayed in a horizontal plane in the lower crown to highly reduced, scale-like leaves appressed to cylindrical stems at the tops of the tallest trees. Previous studies have proposed that this structural variation may reflect gravitational constraints on leaf water relations, but the relationship of leaf structure to leaf functional attributes has not been described. We characterized photosynthetic responses to internal carbon dioxide (Ci) and light in leaves from different crown positions in 8 redwoods 85 to 113 meters tall. The photosynthetic response to Ci indicated significant internal resistance to CO2 diffusion, a likely consequence of greater water stress in upper crown leaves. We conclude that high values of stable C isotope composition of upper crown leaves are attributable to high mesophyll resistance as well as high stomatal resistance relative to photosynthetic capacity. Light compensation and light saturation levels and light-saturated photosynthetic rates all increased with height, the latter (area-based) ranging from 4 to 12 micromol per square meter-second from lower to upper crown. Mass-based rates showed little variation with height. Dark respiration increased relative to photosynthesis with height and provided a basis for estimating the height at which daily leaf C balance would fall to zero.
Key words: redwood, photosynthesis, conductance, carbon isotope