Real-Time Partitioning of Diurnal Stem CO<sub>2</sub> Efflux into Local Stem Respiration and Xylem Transport Processes

Real-Time Partitioning of Diurnal Stem CO<sub>2</sub> Efflux into Local Stem Respiration and Xylem Transport Processes

The apparent respiratory quotient (ARQ) of tree stems, defined as the ratio of net stem CO<sub>2</sub> efflux (E<sub>S_CO2</sub>) to net stem O<sub>2</sub> influx (E<sub>S_O2</sub>), offers insights into the balance between local respiratory CO<sub&...

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Bibliographic Details
Main Authors: Kolby J. Jardine, Regison Oliveira, Parsa Ajami, Ryan Knox, Charlie Koven, Bruno Gimenez, Gustavo Spanner, Jeffrey Warren, Nate McDowell, Guillaume Tcherkez, Jeffrey Chambers
Format: Article
Language:English
Published: MDPI AG 2025-04-01
Series:International Journal of Plant Biology
Subjects:
apparent respiratory quotient (ARQ)
stem CO<sub>2</sub> efflux
stem O<sub>2</sub> influx
CO<sub>2</sub> transport
cellular respiration
stem gas exchange dynamics
Online Access:https://www.mdpi.com/2037-0164/16/2/46
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Summary:The apparent respiratory quotient (ARQ) of tree stems, defined as the ratio of net stem CO<sub>2</sub> efflux (E<sub>S_CO2</sub>) to net stem O<sub>2</sub> influx (E<sub>S_O2</sub>), offers insights into the balance between local respiratory CO<sub>2</sub> production and CO<sub>2</sub> transported via the xylem. Traditional static chamber methods for measuring ARQ can introduce artifacts and obscure natural diurnal variations. Here, we employed an open flow-through stem chamber with ambient air coupled with cavity ring-down spectrometry, which uses the molecular properties of CO<sub>2</sub> and O<sub>2</sub> molecules to continuously measure E<sub>S_CO2</sub>, E<sub>S_O2</sub>, and ARQ, at the base of a California cherry tree (<i>Prunus ilicifolia</i>) during the 2024 growing season. Measurements across three stem chambers over 3–11-day periods revealed strong correlations between E<sub>S_CO2</sub> and E<sub>S_O2</sub> and mean ARQ values ranging from 1.3 to 2.9, far exceeding previous reports. Two distinct diurnal ARQ patterns were observed: daytime suppression with nighttime recovery, and a morning peak followed by gradual decline. Partitioning E<sub>S_CO2</sub> into local respiration and xylem-transported CO<sub>2</sub> indicated that the latter can dominate when ARQ exceeds 2.0. Furthermore, transported CO<sub>2</sub> exhibited a higher temperature sensitivity than local respiration, with both processes showing declining temperature sensitivity above 20 °C. These findings underscore the need to differentiate stem CO<sub>2</sub> flux components to improve our understanding of whole-tree carbon cycling.
ISSN:2037-0164

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