© 1995 Heron Publishing—Victoria, Canada
Changes in respiration and chemical content during autumnal senescence of Populus tremuloides and Quercus rubra leaves
Donald E. Collier (1, 2, 3) and Beverly A. Thibodeau (1)
1. Department of Botany, Erindale College, University of Toronto, Mississauga, Ontario L5L 1C6, Canada / 2. Department of Horticultural Science, University of Guelph, Guelph, Ontario N1G 2W1, Canada / 3. Author to whom correspondence should be addressed / Received February 3, 1995
Summary
Changes in respiration rate, chemical content and chemical concentration were measured in leaves of field-grown Populus tremuloides Michx. and Quercus rubra L. trees throughout the growing season and autumnal senescence. Chlorophyll, soluble sugar, N, P, K and Mg contents and concentrations
all declined during leaf senescence, whereas Ca content and concentration increased. Leaf dry mass per area declined 24 and
35% in P. tremuloides and Q. rubra, respectively, during senescence. In leaves of both species, respiration rates peaked during leaf expansion in the spring
and then declined, as a result of reduced cytochrome-mediated respiration, to reach relatively constant rates by midsummer.
In senescing P. tremuloides leaves, respiration rates remained relatively constant until mid-October and then declined rapidly. In senescing Q. rubra leaves, respiration rates increased in late September, as a result of the appearance of residual respiration that could not
be reduced by respiratory inhibitors, and then declined quickly in early November. No changes in alternative pathway respiratory
activity were observed in leaves of either species during senescence until late autumn when rates declined. Because respiration
rates were correlated with both leaf sugar and nitrogen content during leaf senescence, we conclude that respiration rates
were maintained or increased during leaf senescence to supply energy for degradation and mobilization of chemical constituents.
Keywords:
alternative pathway, cytochrome pathway, nitrogen, sugars.
