PARENT SESSION
Contributed Oral Session 39: Physiology: Respiration, Sap Flow, and Growth
Tuesday, August 9, 8:00 AM - 11:30 AM, Meeting Room 513 E, Level 5, Palais des congrès de Montréal
Physiological basis for age-related decline in photosynthetic capacity in red spruce (Picea rubens).
Adams, Stephanie*,1, Day, Michael1, Greenwood, Michael1, Ward, Margaret1, 1 Dept. of Forest Ecosystem Science, Orono, ME, USA
ABSTRACT- Trees undergo predictable changes in morphology and physiology as they age and some of these changes are linked to an age-related decline in productivity. Many conifer species show a decline in photosynthesis with increasing age, but the physiological mechanisms underlying this are not well understood. Research with ponderosa and lodgepole pines has shown that older trees have the same maximum capacity for photosynthesis as younger trees, but undergo a greater mid-day depression of photosynthesis. This suggests that internal water stress may limit gas exchange through stomatal closure. Previous work with red spruce indicates that the age-related decline in photosynthesis may not be associated with stomatal limitations for this species. We are investigating physiological limitations to photosynthesis in juvenile (7-12 years), mid-age (60-75 years) and old (120-150 years) red spruce trees in a multi-cohort stand in Maine. Photosynthetic rates were measured every two hours on ten trees of each class from dawn until dusk. Light saturated photosynthetic rates of juvenile trees were consistently 50% higher than those of either mid-aged or old trees and diurnal trends were parallel for all age-classes. In addition, we developed empirical A-Ci (assimilation v. internal CO2 concentration) curves for six trees of each age class to calculate carboxylation activity (Vcmax) and electron transport rate (Jmax). Vcmax was 39% lower in mid-age trees than in juvenile and 47% lower in old trees than in juveniles. Jmax was 44% lower in mid-age trees than juvenile and 55% lower in the oldest trees. Chlorophyll concentration exhibited a similar age-related trend. These results suggest that older red spruce trees have an inherently lower photosynthetic capacity, possibly resulting from a lower investment in photosynthetic systems.
Key words: maturation, diurnal trends, old-growth trees, non-stomatal limitations