PARENT SESSION
Oral Session # 24: Photosynthesis and Respiration.
Presiding: A Leakey
Tuesday, August 5. 8:00 AM to 11:30 AM, SITCC Meeting Room 203.

A mass balance approach for calculating stem respiration in trees.

Teskey, Robert^*,1, McGuire, Mary Anne ¹, ¹ University of Georgia, Athens, GA

ABSTRACT- The rate of respiration of a tree stem has commonly been estimated from measurements of CO₂ efflux to the atmosphere. These estimates are based on the assumption that all efflux of CO₂ originates from respiration of local tissues and that all CO₂ produced by local tissues escapes to the atmosphere through the bark. However, dissolved CO₂ can be transported in the xylem and the CO₂ concentration in the stem can be up to three orders of magnitude greater than that of the atmosphere, suggesting that measurements of CO₂ efflux to the atmosphere do not account for all CO₂ produced by respiration. We developed a new mass balance approach for estimating the respiration rate of tree stems that accounts for both external and internal fluxes of CO₂. We demonstrate this approach in three trees of different species using measurements of CO₂ efflux, sap flux, and internal CO₂ concentration to calculate the total rate of CO₂ production of a segment of stem tissue in situ. When we applied the mass balance approach, we found that CO₂ produced by respiration of stem tissues moves in internal and external flux pathways in different proportions at different times of day and in different environmental conditions. Our calculations show that a substantial portion of respired CO₂ is not accounted for in measurements of efflux to the atmosphere alone. In some cases, more than 75% of the respired CO₂ moved in the internal pathway, with less than 25% released to the atmosphere. During daylight hours when sap is flowing, a large proportion of respired CO₂ is carried away in the xylem stream, while at night more respiratory CO₂ escapes to the atmosphere through bark. Measurements made using the mass balance approach can lead to an improved understanding of woody tissue respiration rates.

Key words: internal carbon dioxide transport, plant respiration