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Estimating the CO2 fertilization effect on extratropical forest productivity from Flux-tower observations
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  • Chunhui Zhan,
  • Rene Orth,
  • Hui Yang,
  • Markus Reichstein,
  • Soenke Zaehle,
  • Martin G De Kauwe,
  • Anja Rammig,
  • Alexander J. Winkler
Chunhui Zhan
Technical University Munich, Max Planck Institute for Biogeochemistry

Corresponding Author:[email protected]

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Rene Orth
University of Freiburg, Max Planck Institute for Biogeochemistry
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Hui Yang
Max Planck Institute for Biogeochemistry
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Markus Reichstein
Max Planck Institute fur Biogeochemistry
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Soenke Zaehle
Max Planck Institute for Biogeochemistry
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Martin G De Kauwe
University of Bristol
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Anja Rammig
Technical University Munich
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Alexander J. Winkler
Max Planck Institute for Biogeochemistry
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The land sink of anthropogenic carbon emissions, a crucial component of mitigating climate change, is primarily attributed to the CO₂ fertilization effect on global gross primary productivity (GPP). However, direct observational evidence of this effect remains scarce, hampered by challenges in disentangling the CO₂ fertilization effect from other long-term drivers, particularly climatic changes. Here, we introduce a novel statistical approach to separate the CO₂ fertilization effect on GPP and daily maximum net ecosystem production (NEPmax) using eddy covariance records across 38 extratropical forest sites. We find the median stimulation rate of GPP and NEPmax to be 16.4 ± 4% and 17.2 ± 4% per 100 ppm increase in atmospheric CO₂ across these sites, respectively. To validate the robustness of our findings, we test our statistical method using factorial simulations of an ensemble of process-based land surface models. We acknowledge that additional factors, including nitrogen deposition and land management, may impact plant productivity, potentially confounding the attribution to the CO₂ fertilization effect. Assuming these site-specific effects offset to some extent across sites as random factors, the estimated median value still reflects the strength of the CO₂ fertilization effect. However, disentanglement of these long-term effects, often inseparable by timescale, requires further causal research. Our study provides direct evidence that the photosynthetic stimulation is maintained under long-term CO₂ fertilization across multiple eddy covariance sites. Such observation-based quantification is key to constraining the long-standing uncertainties in the land carbon cycle under rising CO₂ concentrations.
17 Nov 2023Submitted to ESS Open Archive
20 Nov 2023Published in ESS Open Archive