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Biogeosciences An interactive open-access journal of the European Geosciences Union
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https://doi.org/10.5194/bg-2019-291
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2019-291
© Author(s) 2019. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 31 Jul 2019

Submitted as: research article | 31 Jul 2019

Review status
This discussion paper is a preprint. It is a manuscript under review for the journal Biogeosciences (BG).

Partitioning of canopy and soil CO2 fluxes in a pine forests at the dry timberline

Rafat Qubaja, Feyodor Tatarinov, Eyal Rotenberg, and Dan Yakir Rafat Qubaja et al.
  • Department of Earth and Planetary Sciences, Weizmann Institute of Science, Rehovot 76100, Israel

Abstract. Partitioning carbon fluxes is key to understanding the process underlying ecosystem response to change. This study used soil and canopy fluxes with stable isotopes (13C) and radiocarbon (14C) measurements of a 50-year-old dry (i.e., 287 mm of annual precipitation) pine forest to partition the ecosystem’s CO2 flux into gross primary productivity (GPP) and ecosystem respiration (Re) and soil respiration flux into autotrophic (Rsa), heterotrophic (Rh), and inorganic (Ri) components. On an annual scale, GPP and Re were 655 and 488 g C m−2, respectively, with a net primary productivity (NPP) of 276 g C m−2 and carbon-use efficiency (CUE = NPP / GPP) of 0.42. Soil respiration (Rs) made up 60 % of the total ecosystem respiration and was comprised of 24 ± 4 %, 23 ± 4 %, and 13 ± 1 % Rsa, Rh, and Ri, respectively. The contribution of root and microbial respiration to Re increased during high productivity periods, and inorganic sources were more significant components when soil water content was low. Compared to the mean values for 2001–2006 at the same site; (Grünzweig et al., 2009), annual Rs decreased by 27 % to the mean 2016 rates of 0.8 ± 0.1 µmol m−2 s−1). This was associated with decrease in the respiration Q10 values across the same observation by 36 % and 9 % in the wet and dry periods, respectively. Low rates of soil carbon loss combined with relatively high below ground carbon allocation (i.e., 40 % of canopy CO2 uptake) help explain the high soil organic carbon accumulation and the relatively high ecosystem CUE of the dry forest. This was indicative of the higher resilience of the pine forest to climate change and the significant potential for carbon sequestration in these regions.

Rafat Qubaja et al.
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Short summary
This paper provides a combination of the present time and long-term perspective based on study of the CO2 fluxes in a pine forest plantation at the "dry timberline" Negev desert. Two key issues that limit our understanding: The need to know the sources of CO2 fluxes; and the need for long-term perspectives. We provide evidence that help explain the forest plantations productivity under stressful conditions, which can serve in predicting the response of forest to future drying climate.
This paper provides a combination of the present time and long-term perspective based on study...
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