Age-related changes in photosynthesis of woody plants

Woody perennials do not appear to go through a defined senescence phase but do have predictable developmental stages. Reduced photosynthesis and stoma tal conductance have been reported at all developmental transitions, althou gh some studies have shown the opposite. What causes these changes and why do results differ among studies? Do these changes result from or cause chan ges in growth? What are the roles of genetics, size, changing conditions an d cumulative environmental stress in aging trees? Definitive answers remain elusive but recent research is helping to clarify some of the processes as sociated with aging and to point the way for further study.