Seasonal changes in respiratory metabolism of yellow-poplar (Liriodendron tulipifera) branches.
Abstract
Tissue m.c. and rates of CO2 and O2 exchange were determined in the laboratory for branches of L. tulipifera collected at 2 week intervals over a 1 yr period. Av. hourly respiration during the growing season (April-Sept.) was greater for current year twigs (315 mg/m2) than for older branches (175 mg/m2). The respiratory quotient (RQ) varied seasonally, with minima at bud break (March/April), at the period of increased branch and bole growth (June/July) and at the onset of dormancy (Nov./Dec.). Exchange of CO2 and 02 showed a varying degree of positive correlation with tissue m.c.; correlation was strongest for older branches. It is concluded that the high respiratory activity and large surface area of small branches and twigs indicates that they should be considered important when estimating the gaseous exchange and energy flow in forested ecosystems.