Photosynthesis and Respiration of Developing Populus tremuloides Internodes

Abstract

The photosynthetic and respiratory performance of developing internodes of Popudus tremuloides was evaluated by infrared gas analysis.Anatomical and morphological transitions were related to metabolic activity. Photosynthetic rates ranged from 6.0 to 10.0 milligrams CO2 per decimeter squared per hour in the youngest internodes to 2.5 to 3.8 milligrams CO2 per decimeter squared per hour in internodes with fully developed bark tissues. Respiration exceeded the rate of photosynthesis on the average by a factor of two. Stem photosynthesis increased with temperature up to 40°C and declined steeply between 40 and 50°C. Stem respiration increased nearly linearly to temperatures as high as 50°C.In the last twenty years, considerable effort has been devoted to the study of bark photosynthesis (5,10,16,21). Photosynthesis in woody stems is best known in the bark of quaking aspen, Populus tremuloides 17,19,20, 22). Net CO2 assimilation by illuminated aspen bark has never been reported, but photosynthesis (reduction of CO2 release rates on illuminated) is known to occur over a wide range of temperatures and during all seasons of the year (9,10,17).Although the photosynthetic performance of older stem tissues is reasonably well studied, little is known about growing internodes of woody species. Because young, growing stems of woody species intergrade from an entirely primary tissue system to a predominately secondary tissue system, the photosynthetic and respiratory rates of juvenile aspen stem could vary with the age and developmental stage of the internodes. This study was undertaken to investigate developmental changes in aspen internode metabolic rates as related to the plastochron age (7,15)

The Existence of Bark and Stem Photosynthesis in Woody Plants and Its Significance for the Overall Carbon Gain. An Eco-Physiological and Ecological Approach

“…In young twigs of beech with 80-90% respiration reduction, an even higher carbon re-fIxation activity was found. These data are in agreement with those of Foote and Schaedle (1 976a,b) and Brayman and Schaedle (1982).…”

Carbon isotope discrimination in photosynthetic bark

“…(trembling aspen), a broad-leaved, deciduous angiosperm. The capacity of P. tremuloides bark for photosynthetic refixation is well documented (Pearson and Lawrence 1958;Strain and Johnson 1963;Schaedle 1976, 1978;Brayman and Schaedle 1982;Schaedle and Brayman 1986;Kharouk et al 1995). Photosynthetic refixation approaching 80% of dark respiration was recently reported in Pinus monticola branches (Cernusak and Marshall 2000).…”

Age-dependent bark photosynthesis of aspen twigs

“…In P. tremuloides refixation rates ranged from 3.8-6.3 µmol CO 2 m -2 s -1 in the youngest internodes to 1.6-2.4 µmol CO 2 m -2 s -1 in the older ones; corresponding dark respiratory rates were between 18.3 and 4.4 µmol CO 2 m -2 s -1 (Brayman and Schaedle 1982). While Foote and Schaedle (1978) described aspen bark photosynthesis about 5.7-7.6 µmol CO 2 m -2 s -1 , Kharouk et al (1995) reported slightly higher values between 8 and 10 µmol CO 2 m -2 s -1 .…”

“…Nowadays, photosynthesis in woody stems is best known in the greenish cortex of P. tremuloides, but positive net CO 2 assimilation by illuminated aspen bark has never been reported (e.g. Pearson and Lawrence 1958;Strain and Johnson 1963;Schaedle 1976a, b, 1978;Brayman and Schaedle 1982;Cernusak et al 2001). Nevertheless, aspen bark photosynthesis represents an efficient mechanism for the stem-internal re-assimilation of respiratory carbon dioxide, probably contributing to the broad ecological amplitude of trembling aspen (e.g.…”