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Stem Respiration and Carbon Dioxide Efflux of Young Populus deltoides Trees in Relation to Temperature and Xylem Carbon Dioxide Concentration

An Saveyn, Kathy Steppe, Mary Anne McGuire, Raoul Lemeur and Robert O. Teskey
Oecologia
Vol. 154, No. 4 (Jan., 2008), pp. 637-649
Published by: Springer in cooperation with International Association for Ecology
Stable URL: http://www.jstor.org/stable/40213116
Page Count: 13
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Stem Respiration and Carbon Dioxide Efflux of Young Populus deltoides Trees in Relation to Temperature and Xylem Carbon Dioxide Concentration
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Abstract

Oxidative respiration is strongly temperature driven. However, in woody stems, efflux of CO₂ to the atmosphere ( $E_A $ ), commonly used to estimate the rate of respiration ( $R_S $ ), and stem temperature ( $T_{st} $ ) have often been poorly correlated, which we hypothesized was due to transport of respired CO₂ in xylem sap, especially under high rates of sap flow ( $f_s $ ). To test this, we measured $E_A $ , $T_{st} $ , $f_s $ and xylem sap CO₂ concentrations ([CO₂*]) in 3-year-old Populus deltoides trees under different weather conditions (sunny and rainy days) in autumn. We also calculated $R_S $ by mass balance as the sum of both outward and internal CO₂ fluxes and hypothesized that $R_S $ would correlate better with $T_{st} $ than $E_A $ . We found that $E_A $ sometimes correlated well with $T_{st} $ , but not on sunny mornings and afternoons or on rainy days. When the temperature effect on $E_A $ was accounted for, a clear positive relationship between $E_A $ and xylem [CO₂*] was found. [CO₂*] varied diurnally and increased substantially at night and during periods of rain. Changes in [CO₂*] were related to changes in $f_s $ but not $T_{st} $ . We conclude that changes in both respiration and internal CO₂ transport altered $E_A $ . The dominant component flux of $R_S $ was $E_A $ . However, on a 24-h basis, the internal transport flux represented 9-18% and 3-7% of $R_S $ on sunny and rainy days, respectively, indicating that the contribution of stem respiration to forest C balance may be larger than previously estimated based on $E_A $ measurements. Unexpectedly, the relationship between $R_S $ and $T_{st} $ was sometimes weak in two of the three trees. We conclude that in addition to temperature, other factors such as water deficits or substrate availability exert control on the rate of stem respiration so that simple temperature functions are not sufficient to predict stem respiration.

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