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<p>Extreme climatic events are increasing in frequency and intensity in the sub-arctic, a rapidly warming region crucial to global carbon–climate feedbacks. Ecosystem carbon dioxide (CO<sub>2</sub>) fluxes can be greatly impacted by extreme events through both immediate and long-term legacy effects. As event intervals shorten, new extremes may coincide with incomplete recovery from previous ones; yet the consequences of multiple events remain poorly understood. We examined the recovery of tundra CO<sub>2</sub> fluxes relative to untreated controls following extreme drought, winter freezing, and their combination. Mesocosms from two major sub-arctic ecosystem types, <i>Sphagnum</i> peatland and tundra heath, were subjected to a seven-week summer precipitation exclusion (2022) and subsequent winter freezing (− 20&#xa0;°C for two weeks). During summer 2023, drought recovery differed markedly between ecosystem types: <i>Sphagnum</i> peatland had stronger gross primary productivity (GPP) recovery than tundra heath (63 and 41%, respectively). Winter freezing had a similar legacy in both ecosystems (40 and 48% recovery in peatland and tundra heath, respectively). The combined effect of drought and freezing suppressed recovery to the lowest levels (29% in peatland and 19% in tundra heath) but did not differ statistically from freezing alone. In contrast with GPP, ecosystem respiration recovered more strongly (53–69%) across ecosystems and treatments. Importantly, this delayed recovery shifted the summertime net ecosystem exchange toward CO<sub>2</sub> sources (− 0.2 to − 0.3&#xa0;μmol&#xa0;m<sup>−2</sup>&#xa0;s<sup>−1</sup> in peatland and − 0.3 to − 0.7 μmol&#xa0;m<sup>−2</sup>&#xa0;s<sup>−1</sup> in tundra heath), while the controls remained a sink (0.5 and 0.3&#xa0;μmol&#xa0;m<sup>−2</sup>&#xa0;s<sup>−1</sup>, respectively). The combined effect of drought and freezing caused extensive shoot mortality of the dominant dwarf shrub&#xa0;<i>Empetrum hermaphroditum</i> (63% in peatland and 91% in tundra heath). Overall, our results reveal substantial and persistent legacy effects of (multiple) extreme events, potentially amplifying carbon–climate feedbacks.</p>

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CO2 Fluxes Recover Faster from Summer Drought in Sub-arctic Sphagnum Peatland than in Tundra Heath, While Being Similar after Winter Freezing

  • 期刊论文

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  • 发表日期：

    2026年7月7日

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  • Valentin Heinzelmann,
  • Julia Marinissen,
  • Christian Menheere,
  • Rien Aerts,
  • J. Hans C. Cornelissen,
  • Stef Bokhorst

摘要

Extreme climatic events are increasing in frequency and intensity in the sub-arctic, a rapidly warming region crucial to global carbon–climate feedbacks. Ecosystem carbon dioxide (CO2) fluxes can be greatly impacted by extreme events through both immediate and long-term legacy effects. As event intervals shorten, new extremes may coincide with incomplete recovery from previous ones; yet the consequences of multiple events remain poorly understood. We examined the recovery of tundra CO2 fluxes relative to untreated controls following extreme drought, winter freezing, and their combination. Mesocosms from two major sub-arctic ecosystem types, Sphagnum peatland and tundra heath, were subjected to a seven-week summer precipitation exclusion (2022) and subsequent winter freezing (− 20 °C for two weeks). During summer 2023, drought recovery differed markedly between ecosystem types: Sphagnum peatland had stronger gross primary productivity (GPP) recovery than tundra heath (63 and 41%, respectively). Winter freezing had a similar legacy in both ecosystems (40 and 48% recovery in peatland and tundra heath, respectively). The combined effect of drought and freezing suppressed recovery to the lowest levels (29% in peatland and 19% in tundra heath) but did not differ statistically from freezing alone. In contrast with GPP, ecosystem respiration recovered more strongly (53–69%) across ecosystems and treatments. Importantly, this delayed recovery shifted the summertime net ecosystem exchange toward CO2 sources (− 0.2 to − 0.3 μmol m−2 s−1 in peatland and − 0.3 to − 0.7 μmol m−2 s−1 in tundra heath), while the controls remained a sink (0.5 and 0.3 μmol m−2 s−1, respectively). The combined effect of drought and freezing caused extensive shoot mortality of the dominant dwarf shrub Empetrum hermaphroditum (63% in peatland and 91% in tundra heath). Overall, our results reveal substantial and persistent legacy effects of (multiple) extreme events, potentially amplifying carbon–climate feedbacks.