JXB Advance Access published online on November 26, 2008
Journal of Experimental Botany, doi:10.1093/jxb/ern272
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RESEARCH PAPER |
CO2 efflux, CO2 concentration and photosynthetic refixation in stems of Eucalyptus globulus (Labill.)
1Departamento de Egenharia Floresta, Instituto Superior de Agronomia, Universidade Técnica de Lisboa, Tapada da Ajuda, 1349-017 Lisboa, Portugal
2Warnell School of Forestry and Natural Resources, University of Georgia, Athens, GA, USA
3Department of Plant Ecology, University of Bayreuth, D-95440 Bayreuth, Germany
4Instituto Tecnologia Química e Biológica, Oeiras, Portugal
* To whom correspondence should be addressed: E-mail: sofiac{at}isa.utl.pt
In spite of the importance of respiration in forest carbon budgets, the mechanisms by which physiological factors control stem respiration are unclear. An experiment was set up in a Eucalyptus globulus plantation in central Portugal with monoculture stands of 5-year-old and 10-year-old trees. CO2 efflux from stems under shaded and unshaded conditions, as well as the concentration of CO2 dissolved in sap [CO2*], stem temperature, and sap flow were measured with the objective of improving our understanding of the factors controlling CO2 release from stems of E. globulus. CO2 efflux was consistently higher in 5-year-old, compared with 10-year-old, stems, averaging 3.4 versus 1.3 µmol m–2 s–1, respectively. Temperature and [CO2*] both had important, and similar, influences on the rate of CO2 efflux from the stems, but neither explained the difference in the magnitude of CO2 efflux between trees of different age and size. No relationship was found between efflux and sap flow, and efflux was independent of tree volume, suggesting the presence of substantial barriers to the diffusion of CO2 from the xylem to the atmosphere in this species. The rate of corticular photosynthesis was the same in trees of both ages and only reduced CO2 efflux by 7%, probably due to the low irradiance at the stem surface below the canopy. The younger trees were growing at a much faster rate than the older trees. The difference between CO2 efflux from the younger and older stems appears to have resulted from a difference in growth respiration rather than a difference in the rate of diffusion of xylem-transported CO2.
Key words: Eucalyptus globulus, refixation, stem respiration
Received 19 May 2008; Revised 14 September 2008 Accepted 8 October 2008
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