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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-2020-164
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
https://doi.org/10.5194/bg-2020-164
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

Submitted as: research article 25 May 2020

Submitted as: research article | 25 May 2020

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This preprint is currently under review for the journal BG.

Stem and soil nitrous oxide fluxes from rainforest and cacao agroforest on highly weathered soils in the Congo Basin

Najeeb Al-Amin Iddris1, Marife D. Corre1, Martin Yemefack2,3, Oliver van Straaten1,4, and Edzo Veldkamp1 Najeeb Al-Amin Iddris et al.
  • 1Soil Science of Tropical and SubtropicalEcosystems, University of Goettingen, Goettingen, 37077, Germany
  • 2International Institute of Tropical Agriculture, Yaoundé, Cameroon
  • 3now at: Sustainable Tropical Solutions (STS), Yaoundé, Cameroon
  • 4now at: Northwest German Forest Research Institute, Goettingen, 37079, Germany

Abstract. Although tree stems act as conduits for greenhouse gases (GHG) produced in the soil, the magnitudes of tree contributions to total (soil + stem) nitrous oxide (N2O) emissions from tropical rainforests on heavily weathered soils remain unknown. Moreover, soil GHG fluxes are largely understudied in African rainforests, and the effects of land-use change on these gases are identified as an important research gap in the global GHG budget. In this study, we quantified the changes in stem and soil N2O fluxes with forest conversion to cacao agroforestry. Stem and soil N2O fluxes were measured monthly for a year (2017–2018) in four replicate plots per land use at three sites across central and southern Cameroon. Tree stems consistently emitted N2O throughout the measurement period, and were positively correlated with soil N2O fluxes. 15N-isotope tracing from soil mineral N to stem-emitted 15N2O as well as correlations between temporal patterns of stem N2O emissions, soil-air N2O concentration, soil N2O emissions, and vapor pressure deficit suggest that N2O emitted by the stems originated predominantly from N2O produced in the soil. Forest conversion to extensively managed, mature (> 20 years old) cacao agroforestry had no effect on stem and soil N2O fluxes. The annual total N2O emissions were 1.55 ± 0.20 kg N ha−1 yr−1 from the forest and 1.15 ± 0.10 kg N ha−1 yr−1 from cacao agroforestry, with tree N2O emissions contributing 1 to 38 % for forests and 8 to 15 % for cacao agroforestry. These substantial contributions of tree stems to total N2O emissions highlight the importance of including tree-mediated fluxes in ecosystem GHG budgets. Taking into account that our study sites’ biophysical characteristics represented two-thirds of the humid rainforests in the Congo Basin, we estimated a total N2O source strength for this region of 0.18 ± 0.05 Tg N2O yr−1.

Najeeb Al-Amin Iddris et al.

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Replication Data for: Stem and soil nitrous oxide fluxes from rainforest and cacao agroforest on highly weathered soils in the Congo Basin N. Al-Amin Iddris, M. D. Corre, M. Yemefack, O. van Straaten, and E. Veldkamp https://doi.org/10.25625/T2CGYM

Najeeb Al-Amin Iddris et al.

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Short summary
We quantified the changes in stem and soil nitrous oxide (N2O) fluxes with forest conversion to cacao agroforestry in the Congo Basin, Cameroon. All forest and cacao trees consistently emitted N2O, contributing 8–38 % of the total (soil + stem) emissions. Forest conversion to extensively managed (> 20 years old) cacao agroforestry had no effect on stem and soil N2O fluxes. Our results highlight the importance of including tree-mediated fluxes in ecosystem-level N2O budget.
We quantified the changes in stem and soil nitrous oxide (N2O) fluxes with forest conversion to...
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