© 2001 Heron Publishing—Victoria, Canada
Age-related changes in foliar morphology and physiology in red spruce and their influence on declining photosynthetic rates
and productivity with tree age
Michael E. Day (1), Michael S. Greenwood (1) and Alan S. White (1)
1. Department of Forest Ecosystem Science, University of Maine, 5755 Nutting Hall, Orono, Maine 04469-5755, USA / Received September 20, 2000
Summary
The contribution of changes in meristem behavior to age-related decline in forest productivity is poorly understood. We studied
age-related trends in needle morphology and gas exchange in a population of red spruce (Picea rubens Sarg.) growing in a multi-cohort stand where trees ranged from first-year germinants to trees over 150 years old, as well
as in grafted scions from these trees. In the field study, age-related trends in foliar morphology were determined in six
cohorts ranging in age from 2 to 120 years, and differences in gas exchange characteristics were compared between 60- and
120-year age classes. In a common-rootstock study, scions from trees representing 20-, 60-, and 120-year cohorts were grafted
onto juvenile rootstock and maintained for three growing seasons, after which morphological and physiological foliar attributes
were evaluated.
The field study revealed significant age-related trends in foliar morphology, including decreasing specific leaf area, and
increasing needle width, projected area, and width/length ratio. Similar trends were apparent in foliage from the grafted
scions. Both in situ foliage and shoots of grafted scions from the oldest cohort showed significantly lower photosynthetic rates than their counterparts
from younger trees; however, differences in stomatal conductance and internal CO2 concentrations were not significant. These results suggest that: (1) foliage of red spruce exhibits age-related trends in
both morphology and physiology; (2) age-related decreases in photosynthetic rates contribute to declining productivity in
old red spruce; (3) declines in photosynthetic rates result from nonstomatal limitations; and (4) age-related changes in morphology
and physiology are inherent in meristems and persist for at least 3 years in scions grafted to juvenile rootstock.
Keywords:
carbon balance, gas exchange, maturation, ontogeny, sink strength.
