Preprints
https://doi.org/10.5194/bg-2022-37
https://doi.org/10.5194/bg-2022-37
 
08 Feb 2022
08 Feb 2022
Status: this preprint is currently under review for the journal BG.

Temperature sensitivity of soil organic carbon respiration along the Rwenzori montane forests elevational transect in Uganda

Joseph Okello1,2,3,4, Marijn Bauters1,2, Hans Verbeeck2, Samuel Bodé1, John Kasenene3, Astrid Françoys1,5,6, Till Engelhardt7, Klaus Butterbach-Bahl8, Ralf Kiese8, and Pascal Boeckx1 Joseph Okello et al.
  • 1Isotope Bioscience Laboratory – ISOFYS, Ghent University, Coupure Links 653, 9000 Gent, Belgium
  • 2CAVElab- Computational and Applied Vegetation Ecology, Ghent University, Coupure Links 653, 9000 Gent, Belgium
  • 3School of Agriculture and Environmental Sciences, Mountains of the Moon University, P.O Box 837, Fort Portal, Uganda
  • 4National Agricultural Research Organisation, Mbarara Zonal Agricultural Research and Development Institute, P.O Box 389, Mbarara, Uganda
  • 5Soil Fertility and Nutrient Management (SoFer), Ghent University, Coupure Links 653, 9000 Gent, Belgium
  • 6Soil Physics (SoPHy), Ghent University, Coupure Links 653, 9000 Gent, Belgium
  • 7Sweco, Arenbergstraat 13, 1000 Brussels, Belgium
  • 8Institute for Meteorology and Climate Research, Atmospheric Environmental Research (IMK-IFU), Karlsruhe Institute of Technology, Kreuzeckbahnstrasse 19, Garmisch-Partenkirchen 82467, Germany

Abstract. Tropical montane forest store high amounts of soil organic carbon. However, global warming may affect these carbon stocks by enhancing soil organic carbon respiration. Better insight into temperature response of soil organic carbon respiration can be obtained from in and ex situ warming studies. In situ warming via translocation of intact soil mesocosms was carried out along an elevational transect ranging between ca. 1250 m a.s.l. in the Kibale Forest to ca. 3000 m a.s.l. in the Rwenzori Mountains. Samples from the same transect were also warmed ex situ to determine temperature sensitivity. The ex situ results revealed that along the natural climate gradient in the elevational transect, specific heterotrophic CO2 respiration decreased linearly by 1.01 ± 0.12 μg C h−1 g−1 SOC per 100 m of elevation increase. Similarly, the temperature sensitivity increased from 1.50 ± 0.13 in the lowest elevation clusters to 2.68 ± 0.25 in the highest elevation cluster, showing a linear decrease of 0.09 ± 0.03 per 100 m of elevation increase. Additionally, the 13C depletion factor of the respired CO2 decreased linearly by 0.23 ± 0.04 ‰ per 100 m of elevation increase. The results indicate an increased recalcitrance and decreased mineralisation of soil organic carbon with elevation driven by decreasing soil temperature and pH. Subsequently, after two years of in situ warming (0.9 to 2.8 °C), specific heterotrophic soil organic carbon respiration tends to be lower for warmed as compared to control soil. Further, in warmed soils, 13C and content of soil organic carbon relatively increased and decreased, respectively. This indicates increased mineralisation and depletion of readily available carbon during two years of warming. In conclusion, our results suggest that climate warming may trigger enhanced losses of soil organic carbon from tropical montane forests, due to a combination of a higher temperature sensitivity of mineralisation and soil organic carbon content.

Joseph Okello et al.

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on bg-2022-37', Anonymous Referee #1, 22 Mar 2022
    • AC1: 'Reply on RC1', Joseph Okello, 14 Apr 2022
  • RC2: 'Comment on bg-2022-37', Anonymous Referee #2, 24 Mar 2022
    • AC2: 'Reply on RC2', Joseph Okello, 14 Apr 2022

Joseph Okello et al.

Joseph Okello et al.

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Short summary
The increase in global and regional temperatures has the potential to drive accelerated soil organic carbon losses in tropical forests. We simulated climate warming by translocating intact soil cores from higher to lower elevations. The results revealed increasing temperature sensitivity and decreasing losses of soil organic carbon with increasing elevation. Our results suggest that climate warming may trigger enhanced losses of soil organic carbon from tropical montane forests.
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