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Elevated CO2 alters the temperature sensitivity of stem CO2 efflux in a mature eucalypt woodland

  • Noh, Nam Jin
  • Crous, Kristine
  • Salomon Moreno, Roberto Luis
  • Li, Jinquan
  • Ellsworth, David S.
  • Barton, Craig V. M.
  • Pendall, Elise
  • Tjoelker, Mark G.
Publication Date
Jan 01, 2021
Ghent University Institutional Archive
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The CO2 efflux from tree stem surfaces to atmosphere (R-S) is an important component in the carbon (C) balance of forest ecosystems. Rising atmospheric carbon dioxide concentrations [CO2] are expected to stimulate R-S, because of greater C assimilation and carbohydrate supply to stems under rising [CO2]. Growth respiration (R-g) and maintenance respiration (R-m) during the warm growing season may respond differently to rising [CO2] due to different metabolic demands. To test the effect of elevated [CO2] (eCO(2), ambient +150 ppm) on R-S, we examined R-S in mature Eucalyptus trees on a monthly basis for an entire year during the seventh year of exposure to eCO(2). R-S varied seasonally and mirrored seasonal variation in temperature. While R-S was not significantly increased under eCO(2) compared to ambient CO2 (aCO(2)), its temperature sensitivity was significantly decreased (Q(10) of 1.92 for aCO(2) and 1.56 for eCO(2)). The estimated annual R-g accounted for approximately 7-8% of annual total R-S, 419 +/- 103 g C m(-2) yr(-1), indicating that R-m contributes substantially to total R-S in this mature woodland. Monthly mean R-S was correlated with monthly mean soil temperature, soil moisture and monthly stem growth rate in this dry year, but soil moisture levels may have been insufficient to observe the impacts of eCO(2) on stem growth in this droughted and phosphorous limited site. Our results highlight that eCO(2) tends to increase R-m at low temperatures during the non-growing season, thus decreasing the temperature sensitivity of R-S, despite a neutral effect of eCO(2) on R-S rates on a yearly basis.

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